title stringlengths 0 1.13k | abstract stringlengths 1 15.7k | PMID int64 22 36.5M |
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Radioanalytical determination of actinides and fission products in Belarus soils. | Alpha emitting actinides such as plutonium, americium or curium were measured by alpha-spectrometry after radiochemical separation. The short range of alpha-particles within matter requires, after a pre-concentration process, a succession of isolation and purification steps based on the valence states modification of the researched elements. For counting, actinides were electrodeposited in view to obtain the mass-less source necessary to avoid self-absorption of the emitted radiations. Activity concentrations of gamma-emitting fission products were calculated after measurement with high purity germanium detectors (HPGe). These different methods were used to analyse soils sampled in the Republic of Belarus, not far from the Chernobyl nuclear plant. | 18,967,524 |
Determination of bismuth in biological samples using on-line flow-injection microwave-assisted mineralization and precipitation/dissolution for electrothermal atomic absorption spectrometry. | An on-line automated flow injection system with microwave-assisted sample digestion for the electrothermal atomic absorption spectrometric determination of bismuth in biological materials is described. After the exposure of the sample to microwave radiation, the analyte was subject to a precipitation/dissolution process. Bismuth was precipitated with the stannite ion in basic medium and collected on the walls of a knotted coil, while the other matrix components flowed downstream to waste. The precipitate was dissolved with nitric acid and a sub-sample was collected in a capillary of a sampling arm assembly, to introduce 20 mul volumes into the graphite tube by means of positive displacement with air through a time-based injector. The analytical figures of merit were first evaluated by filling the sampling arm with a standard solution of bismuth and thereafter injecting aliquots of this solution into the atomizer. The calibration graph was linear from the detection limit (8 pg) to 1.2 ng of bismuth. The sensitivity was of 26.8 mug l(-1) for 0.2 A-s and the characteristic mass (m(o)) was of 11.8 pg/0.0044 A-s. The precision of the method, evaluated by replicate analyses of solutions containing 20 and 200 pg of bismuth, were 5.5 and 3.0% (n=10), respectively. When solutions were introduced in the flow system here described, the calibration graph was linear in the range 0.04-6.0 mug l(-1), which means that a preconcentration factor of 10 was obtained for bismuth. The precision slightly deteriorated, e.g. the replicate analysis of solutions containing 1 and 10 pg of bismuth were 7.1 and 5.3% (n=10), respectively. However, the recoveries values obtained with urine and whole blood bismuth spiked samples were over 96.5% and the agreement between observed and certified values was good. | 18,967,531 |
Stopped-flow determination of dipyridamole in pharmaceutical preparations by micellar-stabilized room temperature phosphorescence. | The stopped flow mixing technique has been used to study the kinetic determination of dipyridamole by means of micellar-stabilized room temperature phosphorescence (RTP). This mixing system diminishes the time required for the deoxygenation of the micellar medium by sodium sulfite. The phosphorescence enhancers thallium (I) nitrate, sodium dodecyl sulfate (SDS), and sodium sulfite were optimized to obtain maximum sensitivity and selectivity. A pH value of 10.6 was selected as adequate for phosphorescence development. The kinetic curve of dipyridamole phosphorescence was scanned at lambda(ex)=303 nm and lambda(em)=616 nm. Then, the intensity at 10 s, and the maximum slope of phosphorescence development, for an interval time of 1 s, were measured. Two determination approaches: intensity and rate methods, were proposed. The calibration graphs were linear for the concentration range from 50 to 400 ng ml(-1). The detection limits, according to Clayton et al., Anal. Chem. 59 (1987) 2506, were 21.5 and 37.5 ng ml(-1), for intensity and initial rate measurements, respectively. By applying the error propagation theory, the detection limits were 19.0 and 33.0 ng ml(-1), for intensity and initial rate measurements, respectively. Two commercial formulations (persantin and asasantin) were analyzed by both proposed methodologies. Adequate recovery values were obtained in both cases. | 18,967,550 |
Recent advances in the determination of the platinum group elements and gold. | Accurate determinations of the platinum group elements (PGEs) and gold, known as the precious metals, have always been difficult tasks. The metals are often present at trace levels in sample types of complex composition. This situation has improved recently due to developments of instrumental methods and their applications to analyses of the precious metals in a variety of matrices. Attention has been given to determinations of traces of precious metals in biological, clinical and environmental samples. Foremost in importance is inductively coupled plasma mass spectrometry (ICP-MS) which has provided a sensitive means of simultaneous determination of traces of PGEs and gold. Important extensions and improvements in atomic absorption spectrometry (AAS), nuclear and electrochemical methods have been reported also. More research on sample treatments, especially fire assays, applied to PGEs has been carried out. Chlorination has proven to be a viable alternative to fire assays for preconcentration of PGEs and gold in analyses of geological materials. In addition, the recent availability of some additional reference materials will be of great assistance in research work on precious metals. | 18,967,568 |
Solid-phase extraction and spectrophotometric determination of trace amounts of copper in water samples. | A simple method for rapid and selective extraction, preconcentration and determination of copper as it's neocuproine complex by using octadecylsilica membrane disks and spectrophotometry is presented. Extraction efficiency and the influence of flow rates of sample solution and eluent, pH, amount of neocuproine and hydroxylamine hydrochloride, type and least amount of eluent for elution of copper complex from disks, break through volume and limit of detection were evaluated. Also the effects of various cationic interferences on percent recovery of copper were studied. Extraction efficiencies >99% were obtained by elution of the disks with minimal amount of solvent. The limit of detection of the proposed method is 0.12 ppb. The method was applied to the recovery and determination of copper in different water samples. | 18,967,582 |
Direct determination of bismuth, indium and lead in sea water by Zeeman ETAAS using molybdenum containing chemical modifiers. | Direct determination of Bi, In and Pb in sea water samples has been carried out by ETAAS with Zeeman background correction using molybdenum containing chemical modifiers and tartaric acid as a reducing agent. Maximum pyrolysis temperatures and the effect of mass ratios of the mixed modifier components on analytes have been investigated. Mo+Pd+TA or Mo+Pt+TA mixture was found to be powerful for the determination of 50 mug l(-1) of Bi, In and Pb spiked into synthetic and real sea waters. The accuracy and precision of the determination were thereby enhanced. The recoveries of analytes spiked were 94-103% with Mo+Pd+TA or Mo+Pt+TA and they are only 49-61% without modifier. | 18,967,584 |
Normal-phase high-performance liquid chromatographic determination of spiramycin in eggs and chicken. | A precise method is presented for determination of residual spiramycin (SP) in chicken eggs and tissues by high-performance liquid chromatography (HPLC). The sample preparation was performed by homogenizing with a mixture of acetonitrile and n-hexane (5:4, v/v) to minimize the fat amount followed by ultra-filtration using a MolCutII(R). The extracts containing SP were free from interfering compounds when examined by the normal-phase HPLC using a LiChrosorb(R) NH(2) column and a mobile phase of acetonitrile-water (85:15, v/v) with a photo-diode array detector. The average recoveries from spiked SP (0.1, 0.5 and 1.0 ppm) were in excess of 89.0% with coefficients of variation between 1.4 and 2.4%. The limit of detection was 0.1 ppm. | 18,967,619 |
Asynchronous merging zones system: spectrophotometric determination of Fe(II) and Fe(III) in pharmaceutical products. | An asynchronous merging zones was proposed with simultaneous introduction of the sample and of the modifier reagent, ascorbic acid in the studied case, for sequential determination of Fe(II) and Fe(III) in pharmaceutical products. The sample and reagent attained a merging point at different times owing to the use of a delay reactor in the reagent channel. By inserting a large sample and controlling the dispersion in the flow system, Fe(II) and Fe(III) were sequentially measured in the front and in the rear of the sample zone, respectively. The results obtained for Fe redox speciation in pharmaceutical products are in agreement at a 95% confidence level with those obtained with a manual spectrophotometric procedure. The analytical frequency with the proposed flow analysis system was 54 samples h(-1), i.e. 108 determinations h(-1). | 18,967,624 |
The use of 1-[pyridyl-(2)-azo]-naphthol-(2) in the presence of TX-100 and N,N'-diphenylbenzamidine for the spectrophotometric determination of copper in real samples. | A simple and sensitive field detection and spectrophotometric method for determination of copper described herewith is based on the formation of a red coloured species of copper(II) with 1-[pyridyl-(2)-azo]-naphthol-(2) (PAN), TX-100 and N,N'-diphenylbenzamidine (DPBA) at pH range 7.8-9.4. The red coloured Cu(II)-PAN-(TX-100)-DPBA complex in chloroform shows maximum absorbance at 520 nm with molar absorptivity value of 1.14x10(5) l mol(-1) cm(-1). The detection limit of the method is 2 ng ml(-1) organic phase. The system obeys Beer's law up to 0.6 mug Cu(II) ml(-1) in organic solution. Most of the common metal ions generally found associated with copper do not interfere. The repeatability of the method was checked by finding relative standard deviation (RSD) (n=10) value for solutions each containing 0.2 mug ml(-1) of Cu(II) and the RSD value of the method was found to be 1.5%. The validity of the method has been satisfactorily examined for the determination of copper in soil and airborne dust particulate samples. | 18,967,631 |
Electrochemical studies and square wave adsorptive stripping voltammetry of the antidepressant fluoxetine. | The electrochemical reduction of the antidepressant drug fluoxetine was investigated by cyclic, linear sweep, differential pulse and square wave voltammetry using a hanging mercury drop electrode in alkaline buffer solution in water and in a water/acetonitrile mixed solvent. Cyclic voltammograms in aqueous solution showed very strong adsorption of fluoxetine on the electrode with formation of a compact film. The effect of addition of different percentages of acetonitrile on the voltammetric response was evaluated. It is shown that acetonitrile protects the electrode surface, thus preventing the adsorption of fluoxetine as a compact film, although reduction occurs at more negative potentials. Adsorption was used to accumulate the drug onto the electrode surface. The adsorbed species were measured voltammetrically by reduction at -1.3 V in an aqueous 0.05 M Ringer buffer, pH 12, 20% acetonitrile v/v. Linear calibration graphs were obtained in the range 0.52-5.2 M. The quantification of fluoxetine in pharmacological formulations existing in the market was performed using adsorptive square wave cathodic stripping voltammetry. and compared with data from UV spectrophotometry. The method is simple and not time-consuming. A comparative high performance liquid chromatography assay with UV detection was performed. Recovery data for both methods are reported. | 18,967,637 |
pH-Metric determination of acid values in oilseeds without titration. | A new pH-metric method for determination of acid values in oilseeds without titration has been developed in the range 0.6-10 and more mg KOH/g. The method is based on a rapid (1-2 min) selective and complete extraction of free fatty acids from an oilseed test portion into a special reagent A, separation of the solution from the solid oilseed material by centrifugation or filtration, transfer of an aliquot of the solution into a pH-metric cell with reagent B for measurement of conditional pH(1)' of the formed mixture, addition of standard acid (HCl or H(2)SO(4)) and pH(2)' measurement. The reagents are non-toxic, and the method is rapid. Its metrological parameters for Soybean, Canola and Sunflower oilseeds are satisfactory for practical purposes. | 18,967,639 |
In-situ external reflection FTIR spectroelectrochemical and XPS investigations of cobalt-cyanometallates as inorganic polymeric materials on a platinum electrode. | Cobalt-cyanometallate films electrochemically deposited on a platinum electrode were studied by cyclic voltammetry (CV), in-situ FTIR spectroelectrochemistry (FTIRs) and potential resolved XPS measurements. The experimental results reveal that the CoHCF film on Pt electrode exists in two forms. The major form of the inner layer of the film is (M(+))(2)Co(II)Fe(II)(CN)(6) where M(+)denotes a cationic counter ion, in which both the Fe(2+)and Co(2+)centers can be oxidized to Fe(3+)and Co(3+)in the potential range of 0-1.0 V vs. Ag/AgCl in NaCl solution. The major form of the outer layer is Co(II)(2)Fe(II)(CN)(6), in which electrochemical reactions in this potential range are limited by kinetic sluggishness. The FTIR and XPS spectra indicated that the Co centers change from high-spin state to low-spin state accompanying the Co(2+)/Co(3+)oxidation reaction. In addition, the cations' effect on electrochemical reactions of CoHCF is also discussed. | 18,967,647 |
Transport of organic dyes through ether-type polyurethane membrane. | Transport of various anthraquinone, acidic and basic dyes in aqueous solution through ether-type polyurethane membrane has been studied to better define the factors affecting the removal of organic compounds by the polyurethane membrane and to complement the previously proposed sorption mechanism. The effects of pH, salts, dye geometry and size, initial dye concentration, thickness of the membrane, and solution temperature on the rate of transport were investigated. Transport was found to be dependent upon the pH conditions of the starting and the receiving solutions. An increased rate of transport was observed with increased solution temperature and with the use of a thinner polyurethane membrane. The differences in the rates of transport can be attributed to the relative solubility of the organic dyes in the membrane and in solution, and to the strength and extent of intermolecular interactions with the polymer. Dye concentration, geometry and size, and the presence of salts in solution had no significant effect on the rate of transport. All of the studied dyes were found to exist as neutral species in the membrane. | 18,967,652 |
Modelling the matrix interference of iron in the multivariate determination of copper by stripping voltammetry Instrument standardization. | Two different standardization procedures have been applied in order to minimize the experimental effort necessary to determine copper in presence of iron by differential pulse anodic stripping voltammetry. The significant matrix interference caused by iron in the voltammetric determination of copper has been successfully solved by using partial least squares (PLS) regression. The use of this multivariate regression implies a large number of training set samples, so a standardization method was required. In fact, the standardization methods used have reduced the calibration samples needed in future determinations by up to 75%. Moreover, PLS regression allowed both metals to be determined simultaneously by using an adequate experimental design, without any limitation to their respective concentrations and without the need to know the level of interference. | 18,967,656 |
Determination of Cu(II) and Zn(II) using silica gel loaded with 1-(2-thiasolylazo)-2-naphthol. | The silica gel with 1-(2-thiasolylazo)-2-naphthol adsorbed was obtained. The adsorption of Cu(II) and Zn(II) from an aqueous solution onto loaded silica gel was studied. The capabilities of 1-(2-thiasolylazo)-2-naphthol immobilized for Cu(II) and Zn(II) preconcentration, visual and diffusion reflectance spectroscopic detection was evaluated. The detection limits were 10 and 15 microg.l(-1), respectively. Visual test scales for metal ions determination in the range 0.65-13 microg per sample were worked out. The developed methods were applied to Cu(II) and Zn(II) determination in natural and tap water. The obtained results agreed well with the reported value. | 18,967,666 |
Does the chromatomembrane cell improve the quality of environmental analysis? | With the intention of combining partition chromatography and membrane techniques, we succeeded in developing the chromatomembrane cell which has proved to be reliable as an extraction and preconcentration manifold in flow injection analysis. With this technique, two immiscible phases can be induced to flow independently through a block of biporous (macro and micro) PTFE in order to promote analyte exchange. Consequently, the application of chromatomembrane cells in environmental analysis resolves all problems of sample pretreatment simply and effectively whenever a preconcentration step by gas/liquid or liquid/liquid solvent extraction is included. The link-up with analyzers (AAS, UV-Vis photometry, GC, IC, HPLC, voltammetry, ion selective electrodes, etc.) makes possible computer aided automization for environmental monitoring. | 18,967,674 |
Simultaneous potentiometric determination of ClO(3)(-)-ClO(2)(-) and ClO(3)(-)-HClO by flow injection analysis using Fe(III)-Fe(II) potential buffer. | A rapid potentiometric flow injection technique for the simultaneous determination of oxychlorine species such as ClO(3)(-)-ClO(2)(-) and ClO(3)(-)-HClO has been developed, using both a redox electrode detector and a Fe(III)-Fe(II) potential buffer solution containing chloride. The analytical method is based on the detection of a large transient potential change of the redox electrode due to chlorine generated via the reaction of the oxychlorine species with chloride in the potential buffer solution. The sensitivities to HClO and ClO(2)(-) obtained by the transient potential change were enhanced 700-800-fold over that using an equilibrium potential. The detection limit of the present method for HClO and ClO(2)(-) is as low as 5x10(-8) M with use of a 5x10(-4) M Fe(III)-1x10(-3) M Fe(II) buffer containing 0.3 M KCl and 0.5 M H(2)SO(4). On the other hand, sensitivity to ClO(3)(-) was low when a potential buffer solution containing 0.5 M H(2)SO(4) was used, but could be increased largely by increasing the acidity of the potential buffer. The detection limit for ClO(3)(-) was 2x10(-6) M with the use of a 5x10(-4) M Fe(III)-1x10(-3) M Fe(II) buffer containing 0.3 M KCl and 9 M H(2)SO(4). By utilizing the difference in reactivity of oxychlorine species with chloride in the potential buffer, a simultaneous determination method for a mixed solution of ClO(3)(-)-ClO(2)(-) or ClO(3)(-)-HClO was designed to detect, in a timely manner, a transient potential change with the use of two streams of potential buffers which contain different concentrations of sulfuric acid. Analytical concentration ranges of oxychlorine species were 2x10(-5)-2x10(-4) M for ClO(3)(-), and 1x10(-6)-1x10(-5) M for HClO and ClO(2)(-). The reproducibility of the present method was in the range 1.5-2.3%. The reaction mechanism for the transient potential change used in the present method is also discussed, based on the results of batchwise experiments. The simultaneous determination method was applied to the determination of oxychlorine species in a tap water sample, and was found to provide an analytical result for HClO, which was in good agreement with that obtained by the o-tolidine method and to provide a good recovery for ClO(3)(-) added to the sample. | 18,967,677 |
Chromium speciation using an automated liquid handling system with inductively coupled plasma - mass spectrometric detection. | The speciation of inorganic chromium in environmental samples is required for accurate assessment of pollution levels. Of the two chromium oxidation states, Cr (VI) is a known carcinogen, while Cr (III) is an essential element. Total chromium measurement cannot be used to determine actual environmental impact due to the considerable difference in toxicity of the two elemental forms. An automated liquid handling system, the PrepLabtrade mark, can be used with an inductively coupled plasma-mass spectrometer (ICP-MS) to quantify Cr (III) and Cr (VI) in liquid samples. An autosampler is used to introduce discrete sample volumes into a solid-phase chelation resin column. The Cr (III) and Cr (VI) species are separated and are introduced on-line into the VG PlasmaQuad 3 ICP-MS for detection. The chromatographic data are collected in time resolved analysis mode with the capability of simultaneous multiple-isotopic detection. | 18,967,681 |
Flow-injection spectrophotometry of manganese by catalysis of the periodate oxidation of 2,2'-azinobis(3-ethylbenzothiazoline-6-sulfonic acid). | A sensitive flow-injection spectrophotometric procedure is proposed for the determination of manganese(II), based on its catalytic effect on the oxidation of 2,2'-azinobis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) with periodate. By monitoring the change in absorbance of the oxidation product of ABTS at 415 nm, manganese(II) in the range 0.05-1.0 ng ml(-1) can be determined with a sampling frequency of 30 h(-1). A relative standard deviation (R.S.D.) (n=10) is 1.6% at the 0.5 ng ml(-1) level. The proposed method suffers from few interferences and has been successfully applied to the determination of manganese in river, lake and seashore water samples. | 18,967,685 |
Speciation of arsenic and selenium compounds by HPLC hyphenated to specific detectors: a review of the main separation techniques. | This review deals with liquid phase separation of major arsenic and selenium species followed by element specific detection. It concerns papers published since 1980 and describing only currently used methods that were or could be applied to As and Se speciation in environmental matrices. Methods performances are compared on the basis of efficiency, rapidity, absolute and concentration detection limits and applicability to real world environmental samples. | 18,967,689 |
A miniaturized urea sensor based on the integration of both ammonium based urea enzyme field effect transistor and a reference field effect transistor in a single chip. | A urea biosensor prepared by covalent binding of urease directly to the surface of an ammonium-sensitive field effect transistor (FET) is described. Nonactin incorporated in carboxylated polyvinyl chloride was used to obtain the sensitive membrane of the ammonium-sensitive FET. The grafting of urease on the polyvinylchloride-COOH membrane surface was performed through carbodiimide coupling. The activity of the immobilized enzyme was spectrometrically controlled through the time-dependent disappearance of the absorbance of NADH at 340 nm. An apparent activity of 50% was found, compared with free enzyme. The sensitivity of the urea enzyme FET is 50 mV/pUrea working in a differential mode of 2 muM to 1 mM, this sensitivity being constant during 15 days. Finally, in order to test the potentialities of the urea biosensor for the environmental applications, the detection of heavy metal ions such as Cu(II) and Hg(II) in solution was performed by measuring the remaining activity of the inhibited enzyme. | 18,967,711 |
Poly(vinyl chloride)-based macrocyclic membrane sensors for magnesium. | Poly(vinyl chloride)-based membranes of macrocycles 4,11-dimethyl-2,4,9,11-tetraethyl-1,5,8,12-tetraaza cyclotetradeca-1,8-diene (I) and 4,11-dioxa-2,9-dimethyl-1,5,8,12-tetraaza cyclotetradeca-1,8-diene (II) with sodium tetraphenyl borate (STB) as an anion excluder and dibutyl phthalate (DBP), dioctyl phthalate (DOP), dibutylbutyl phosphonate (DBBP) and 1-chloronaphthalene (CN) as plasticizing solvent mediators were prepared and investigated as magnesium selective electrodes. The best performance was observed having the composition (II)-PVC-STB-DBP in the ratio 2:10:1:7, which works well over a wide concentration range (1.9x10(-6) to 1.0x10(-1) M) with a Nernstian slope of 29 mV per decade of activity between pH 2.5 and 6.5. These electrodes have been found to be chemically inert showing a fast response time of 15 s and were used over a period of 3 months with good reproducibility (S=+/-0.2 mV). The selectivity coefficient values for mono-, di- and trivalent cations indicate excellent selectivity for Mg(2+) over a large number of cations. The electrodes have also been used successfully in partially non-aqueous medium and as an indicator electrode in the potentiometric titration of Mg(2+) with EDTA. Anions such as Cl(-) and SO(4)(2-) do not interfere in the working of the electrode. The practical utility of the membrane sensor has also been observed in solutions contaminated with detergents (cetyltrimethyl ammonium bromide and sodium dodecyl sulphate). Above all, the membrane sensor has been very successfully used to analyse some babyfood products and soft drinks for the determination of Mg(2+). | 18,967,740 |
Determination of tungsten in niobium-tantalum, vanadium and molybdenum bearing geological samples using derivative spectrophotometry and ICP-AES. | Two different procedures, one using derivative spectrophotometry and another using inductively coupled plasma atomic emission spectrometry (ICP-AES) have been developed for the determination of tungsten in niobate-tantalates, tin slag samples, ores, concentrates and vanadium and molybdenum bearing geological materials. In the first method involving derivative spectrophotometry, 0.05-0.5 g of the sample is fused with sodium hydroxide, the tungsten is extracted by leaching the melt with distilled water and estimated as thiocyanate using a second derivative spectrophotometric method in the presence of interferents, i.e. Nb, Mo and V, without separating them. Mixtures of tungsten with V, Nb and Mo are used for standardizing the various parameters like zero-crossing wavelength, wavelength range, etc. Tolerance limits for V, Nb and Mo have also been evaluated. In the second method involving ICP-AES, 0.05-0.5 g of sample is fused with KHSO(4) to a clear melt and dissolved in ammonium oxalate solution. Ammonium hydroxide precipitation is then carried out to separate Nb and Ta as hydroxides and the filtrate is boiled with nitric acid to destroy the oxalates before aspiration into the plasma for measurement of tungsten values by ICP-AES using the 207.911 nm emission line. Both methods have been applied to niobate-tantalate and tin slag samples and the results obtained are reported in this paper. The values obtained by both methods are in good agreement with each other. The proposed methods have also been applied to the determination of tungsten in two Canadian Certified Reference Standards (CT-1 and MP-2) and the values obtained are in good agreement with the certified values and the R.S.D.% in case of the ICP-AES method varied from 1-2% at >1000 mug g(-1) level to 9.4% at the 20 mug g(-1) level whereas the R.S.D.% in case of the derivative method varied from 1 to 7.8%. | 18,967,758 |
Complexation and determination of palladium (II) ion with para-Cl-phenylazo-R-acid spectrophotometrically. | The complexation of para-Cl-phenylazo-R-acid azo dye with Pd(II) has been studied spectrophotometrically. Protonation constant (pK(a)) of the ligand has been calculated and the stability conditional constants of para-Cl-phenylazo-R-acid ligand with palladium ion has been determined at a constant temperature (25.0 degrees C), where the molar ratio of this complex is 1:1 (metal:ligand) with logbeta(1)=3.75, and 1:2 with logbeta(2)=8.55. Solid complex of para-Cl-phenylazo-R-acid has been prepared and characterized on the basis of elemental analysis and FTIR spectral data. A procedure for the spectrophotometric determination of Pd(II) using para-Cl-phenylazo-R-acid as a new azo chromophore is proposed where it is rapid, sensitive and highly specific. Beer's law was obeyed in the range 0.50-10.00 ppm at pH 5.0-6.0 to form a violet-red complex (epsilon=7.7 x 10(4) l(-1) mol(-1) cm(-1) at lambda(max)=560 nm). Metal ions such as Cu(II), Cr(III), La(III), Yb(III), Y(III), and Rh(III) interfere with the complex. Ammonium salt of trimellitic acid is used to precipitate some of the interfering ions and a scheme for separation of Pd(II) from a synthetic mixture similar in composition to platinum ore or deposit was made. | 18,967,771 |
Sequential injection spectrophotometric assay of bromazepam complexed with iron(II) in hydrochloric acid with chemometric optimization. | A sequential injection spectrophotometric method for the assay of bromazepam anxiolytic drug has been reported. The method is based on the complexation reaction of bromazepam with iron(II) in hydrochloric acid media and spectrophotometrically measuring the product at lambda(max)=585 nm. A comprehensive chemometrical optimization treatment was successfully utilized for determining the proper optimum operating conditions for both the system and the chemical variables. The experimental design approach was employed and a 2(k) factorial design was run for studying the interaction effects of four factors namely, hydrochloric acid concentration, iron(II) concentration, delay time and flow rate. The super modified simplex algorithm was utilized for optimizing the three highly interacting factors which were, hydrochloric acid, iron(II), and delay time. The conditions obtained were 150 microl 0.110 mol l(-3) hydrochloric acid, 75 microl 0.328 mol l(-3) iron(II), 1200 s delay time and 40 microl s(-1) flow rate. The method was found to be suitable for the determination of Bromazepam in pharmaceutical preparations and the results obtained for the assay of the compound in proprietary drugs indicate that the method suffers no interference from excipients. | 18,967,774 |
Pushing the detectability of voltammetry: how low can we go? | The coupling of adsorptive accumulation with catalytic reactions results in remarkably low (sub-picomolar) detection limits. This review assesses various strategies for attaining such dual-amplification effects, that lead to the most sensitive voltammetric technique, adsorptive-catalytic stripping voltammetry (AdCtSV). | 18,967,784 |
On the acid behaviour of the alcoholic group of serine. | The behaviour of l-serine in strongly alkaline solution was studied at 25 degrees C and in 3.00 mol/l NaClO(4), as a constant ionic medium, to obtain quantitative information about the eventual dissociation of its alcoholic group. A spectrophotometric method was employed to measure the free concentration of hydrogen ions. Two indicators, methyl thymol blue and eriochrome blue type R, were used. Their values as protonation constants and absorbance coefficients were determined in advance. The method here proposed has been validated beforehand by applying it to d-mannite and glycerine and by comparing results so obtained with those previously provided by literature. The investigation showed weak acid properties of the -OH of serine and its dissociation constant was determined. Polynuclear species or further dissociation were not observed. | 18,967,793 |
pH-Metric method for acid number determination in hydraulic oils without titration. | A heptane-mediated extraction of acids from hydraulic oils is proposed for pH-metric acid number determination without titration. The acids are extracted in the reagent consisting of triethanolamine and potassium nitrate dissolved in water and isopropanol. The use of heptane allows us to overcome the influence of additives in the hydraulic oil on the glass electrode. Simultaneously the extraction of acids from the oil into the water-isopropanol phase is simplified. The method is validated and suitable metrological characteristics of the acid number determination are obtained. | 18,967,808 |
Copper determination in natural water samples by using FAAS after preconcentration onto amberlite XAD-2 loaded with calmagite. | A procedure for separation and preconcentration of trace amounts of copper in natural water samples, has been proposed. It is based on the adsorption of copper(II) ions onto a column of Amberlite XAD-2 resin loaded with calmagite reagent. This way amounts of copper within the range from 0.0125 to 25.0 microg, in a sample volume of 25 to 250 ml, and pH from 3.7 to 10.0 was concentrated as calmagite complex in a column of 0.50 g of Amberlite XAD-2 resin. Copper (II) ion was desorpted by using 5.0 ml of 2 mol l(-1) hydrochloric acid. Detection and determination limits of the proposed procedure for 250 ml sample volume were 0.15 and 0.50 microg l(-1), respectively. Selectivity test showed that (in the indicated concentration), calcium(II) (500 mg l(-1)), magnesium(II) (500 mg l(-1)), strontium(II) (50 mg l(-1)), iron(III) (10 mg l(-1)), nickel(II) (10 mg l(-1)), cobalt(II) (10 mg l(-1)), cadmium(II) (10 mg l(-1)) and lead(II) (10 mg l(-1)) did not interfere in copper determination by this procedure. Precision of the method, evaluated as the relative standard deviation by analyzing a series of seven replicates, was 2.42% for a copper mass of 1.0 microg in a sample volume of 100 ml. The accuracy of the proposed procedure was evaluated by means of copper determination in reference biological samples. The achieved results were in good agreement with certified values. The extractor system had a sorption capacity of 1.59 mumol of copper per gram of resin loaded with calmagite. The proposed procedure was applied for copper determination by FAAS in natural water samples. Samples were collected from different places of Salvador city, Bahia, Brazil. The achieved recovery, measured by the standard addition technique, showed that the proposed procedure had good accuracy. A good enrichment factor (50x) and simplicity are the main advantages in this analytical procedure. | 18,967,821 |
(C70)2-p-tert-butylcalix[6]arene complex films on electrodes catalyze the reduction of nitrite ions. | (C70)(2)-p-tert-butylcalix[6]arene complex films on GC electrode surface showed two couples of redox reactions in mixed solvent of (1:1, v:v) acetonitrile and water containing tetra-butylammonium perchlorate. The electrocatalytic reduction for nitrite by these films was observed, indicating that (C70)(2)-p-tert-butylcalix[6]arene is capable of mediating the electron transfer to nitrite. | 18,967,827 |
Simultaneous determination of manganese and zinc in mixtures using first- and second-derivative spectrophotometry. | A new direct spectrophotometric determination of manganese with 5,8-dihydroxy-1,4-naphthoquinone (naphthazarin,NAZA) is reported. Absorption maximum, molar absorptivity and Sandell's sensitivity of 1:2 (M:L) complex are 695 nm, 1.88x10(4) l mol(-1) cm(-1) and 2.92 ng cm(-2), respectively. A linear calibration graph is obtained up to a concentration of 7.2 mug ml(-1) of manganese. The optimum range for determination (Ringbom) is between 0.20 and 6.8 mug ml(-1). A rapid method for simultaneous determination of manganese and zinc in their mixture using derivative spectra is described. The range 0.28-5.6 mug ml(-1) manganese could be determined in the presence of 0.33-6.8 mug ml(-1) zinc and vice versa. The developed method was applied to the simultaneous spectrophotometric determination of manganese and zinc in some synthetic mixtures and was found to give satisfactory results. | 18,967,835 |
Donnan dialysis of copper, gold and silver cyanides with various anion exchange membranes. | Donnan dialysis is an ion exchange membrane process that can be used for the purification and concentration of diluted solutions. In this work, the behaviour of gold, silver and copper in cyanide medium is examined. Flux of cyanide complexes and corresponding free cyanide are determined using five commercial anion exchanger membranes (AMV, ACS, RAI 5035, ADP and ADS). The results show that the rate transfer depends upon the nature of the anion exchanger membrane. It is observed that the species number in the feed solution influences the transfer selectivity of metal ion complex against free cyanide Thus, gold which forms only one stable species with cyanides is transferred faster through an ACS membrane than copper which forms three species. However, this result is not verified when an ADS membrane is used. A model of the complex transfer through anion exchange membranes based on Donnan dialysis is proposed. A three compartment Donnan dialysis is performed to improve the separation between the studied metals. Decyanidation is also examined and separation factors are calculated. It is shown that Donnan dialysis can be an efficient technique for the separation of cyanides complexes of copper, gold and silver when parameters such as anion exchange membrane and the number of compartments are optimised. An advantage of this technique is also the possibility of recycling all reactants with a good impact on the environment. | 18,967,859 |
Analysis of archaeological samples and local clays using ICP-AES, TG-DTG and FTIR techniques. | The spectrochemical and thermal analysis of different archaeological samples as bricks, terra-cotta and local clays were carried out. The concentration of major and minor elements of samples was determined by sequential inductively coupled plasma atomic emission spectrometry. The method was tested by determining Si, Al, Fe, Ca, Mg, Mn, Pb, Cu, Zn, Ti, Na and K in the standard solutions and reference material GXR-4. The precision of the determination (relative standard deviation) ranged from 0.4 to 1.54%. The clay minerals are the main materials for the production of bricks and terra-cotta figures. Thermogravimetric (TG) and differential (TG-DTG) analysis and Fourier transform infrared spectrometry (FTIR) methods can be used for the study of characteristic reactions, associated with the course of the heating. The TG-DTG curves were obtained in the temperature range 25-900 degrees C, and the dynamic experiment was carried out in the air and nitrogen atmosphere. The infrared evolved gas analysis was performed using FTIR in the dynamic nitrogen atmosphere. | 18,967,866 |
Simultaneous determination of ethanol and glycerol in wines by a flow injection-pervaporation approach with in parallel photometric and fluorimetric detection. | A simultaneous method for the determination of ethanol and glycerol in wines based on the coupling of pervaporation-chemical derivatisation-photometric detection for ethanol and biochemical derivatisation-fluorimetric detection for glycerol is proposed. After separation by pervaporation the ethanol is collected in a K(2)Cr(2)O(7) acceptor stream and the Cr(3+) formed is driven to the spectrophotometer and monitored at 600 nm. The determination of glycerol is based on its oxidation by oxidised beta-nicotinamide adenine dinucleotide (beta-NAD(+)) catalysed by glycerol dehydrogenase immobilised on controlled-pore glass, the reduced form of the coenzyme (NADH) being spectrofluorimetrically monitored (lambda(ex)=340 nm, lambda(em)=460 nm). The linear determination range is between 1-20% for ethanol and 2-8 g l(-1) for glycerol, with RSDs 3 and 2%, respectively. The method applied to red and white Spanish wines, compares well with the official methods for these analytes. | 18,967,879 |
Enrichment of benzo[a]pyrene in vegetable oils and determination by HPLC-FL. | We have developed a simple method for the determination of the carcinogen Benzo[a]pyrene (BP) in vegetable oils. The method consists of extraction of the vegetable oil in acetonitrile, concentration to dryness in rotary evaporator and redissolution of the residue in hexane. The purification of the hexane extract was on Sep-Pack Silica Plus cartridges, and the determination of the BP in the isolated extract was by HPLC-FL. Detection and quantification limits were 0.23 and 0.32 mug kg(-1) of olive oil, respectively. Recovery (>93%) and RSD (<4%) were satisfactory. When applied to 18 oil samples, BP levels varied from not detected to 1.99 mug kg(-1). | 18,967,938 |
Application of H-point standard additions method to spectrophotometric and spectrofluorimetric determinations of glafenine and glafenic acid in mixtures. | H-point standard additions method (HPSAM), based on spectrophotometric and spectrofluorimetric measurements, was proposed for simultaneous determination of glafenine (G) and glafenic acid (GA). A study of the absorption spectra of G and GA in various pH media has been carried out. Reasonably resolved UV-absorption spectra were obtained with a solution adjusted at pH 4.5 with citric acid-phosphate buffer. Additionally, the fluorescence properties in aqueous micellar systems of anionic, cationic and non-ionic surfactants were investigated. Well resolved fluorescence spectra were established in aqueous Triton X-100 solution at pH 7.8 (citric acid-phosphate buffer). As a comparative method, UV-derivative spectrophotometry (based on zero-crossing technique) was suggested. First-derivative value at 352 nm ((1)D(352)) and second-derivative value at 366 nm ((2)D(366)) were selected for the quantification of G and GA, respectively. The relative standard deviations of the proposed methods approximate 2%. The proposed methods were evaluated through the analysis of commercial tablets. The results were accurate and precise. | 18,967,954 |
Potentiometric determination of dialysate urea nitrogen. | An enzymatically modified ammonium ion-selective electrode has been applied for the determination of urea in spent dialysate. The biosensor has been used in a simple flow-injection analysis (FIA) system. The system enables one to perform over 25 dialysate urea nitrogen (DUN) determinations per hour. The interferences from other components of posthemodialysis fluid were eliminated by simultaneous measurements with non-modified enzymatically ion-selective electrode. It is possible to use both the sensors in a simplified differential potentiometric system. The results of DUN determination using the biosensor/FIA system and a conventional method of urea determination were comparable. The presented analytical system can potentially find wider biomedical application in the monitoring of hemodialysis progress. | 18,967,957 |
Sequential injection system for the spectrophotometric determination of reducing sugars in wines. | A sequential injection system for the spectrophotometric determination of reducing sugars in wines is described. The methodology is based on the formation of a coloured complex produced by the reaction of copper (I) with 2,9-dimethyl-1,10-phenanthroline (neocuproine), after reduction of copper (II) to copper (I) by reducing sugars. In the present SI system, a dialysis unit was incorporated not only to allow the sample dilution, but also to minimise the interference of some coloured compounds. In this way, direct sample introduction into the system was possible, without any previous treatment of the wine samples. The proposed method can be applied to the determination of reducing sugars in two concentration ranges: from 2 to 25 g l(-1) (table wines) and from 20 to 140 g l(-1) (Port wines). To perform determinations in these two ranges, the manifold configuration remained the same; just a few operational parameters were changed in the controlling software. A sampling-rate of 14-18 samples per hour was obtained with good repeatability for ten consecutive injections of wine samples (relative standard deviations (RSD) <2.1%). The results obtained from 19 wine samples were comparable to those obtained by the reference method. | 18,967,962 |
Determination of antibacterial reagents by liquid chromatography-electrospray-mass spectrometry. | This paper describes a newly developed liquid chromatography-electrospray-mass spectrometry (HPLC-ES-MS) method for the determination of 13 antibacterial reagents (olaquindox, trimethoprim, clopidol, ormethoprim, morantel, carbadox, thiamphenicol, pyrimethamine, furazolidone, oxolinic acid, difurazon, nalidixic acid, piromidic acid). The optimization for the detection of these compounds by HPLC-ES-MS was investigated. A C(18) column with gradient elution was utilized for the separation of thirteen antibacterial chemicals. Collision induced dissociation (CID) was used to induce fragmentation of analyte molecules and enhance the specificity of the method. Selective ion monitoring (SIM) was employed for quantitative determination. The detection limit of this method proved to be much better than previously reported ones. Satisfactory linearity, 0.5-10 ppm, of each compound was obtained. A solvent extraction method to extract analyte compound from pork was developed. The application of this newly developed method was demonstrated by analyzing antibacterial reagent added pork samples. | 18,967,971 |
Flow injection determination methods of ascorbic acid. | A review with 100 references is presented to show the advantages involved in the use of flow injection analysis (FIA) for the determination of ascorbic acid. The FI methods proposed for the determination of ascorbic acid are described and compared according to the used detection technique. Analytical figures of merit and interferences are also discussed. | 18,967,995 |
Selectivity assessment of a sequential extraction procedure for metal mobility characterization using model phases. | This study considers the selectivity of the extractants used in a sequential extraction scheme for metals mobility assessment by analyzing individual mineral phases previously coprecipitated or sorbed with trace metals. The scheme evaluated was a modification of the Tessier et al. [A. Tessier, P.G.C. Campbell, M. Bisson, Anal. Chem. 51 (1979) 844] sequential procedure proposed by the authors. The phases studied were calcite, amorphous iron oxide, hausmannite, humic acid, kaolinite and illite. Selective extractions were obtained for As, Cr, Cu, Ni, Pb and Zn in metal-coprecipitated phases whereas NH(2)OH-HCl was not selective for the extraction of Hg and Cd coprecipitated in hausmannite and amorphous iron oxide, respectively. Otherwise, Cd, Hg, Ni and Zn sorbed on the different phases were released with MgCl(2) and NaOAc/HOAc, but stronger reagents were needed to release As, Cr, Cu and Pb. | 18,968,015 |
On the improvement of solid-phase extraction room-temperature phosphorimetry for the analysis of polycyclic aromatic hydrocarbons in water samples. | This article presents considerable improvements in SPE-RTP methodology for the analysis of polycyclic aromatic hydrocarbons in water samples. Bulky glassware and vacuum pump were removed from the previous extraction procedure [E.D. Hagestuen, A.D. Campiglia, Talanta 49 (1998) 547] by processing 10 ml of sample with syringes and stainless steel filter holders. The oven-drying step was substituted by air sample drying, which employed positive pressure to remove water excess from the extraction membrane. As a result, analysis times from 8 to 10 min per sample were obtained. No costs in levels of detection were observed. Limits of detection at the pg ml(-1) level were estimated for phenanthrene, pyrene, benzo(k)fluoranthene, benzo(a)pyrene, and chrysene. The feasibility of identifying single components in PAH mixtures was investigated. Binary and tertiary mixtures were resolved by appropriate choice of excitation and emission wavelengths. The advantage of using excitation-emission matrix analysis was demonstrated for a six-component mixture. | 18,968,032 |
Atomic absorption spectrometric determination of calcium and other metallic elements in some animal protein sources. | The phosphorus content of some animal protein sources was determined in order to identify the sample with the highest phosphorus content for use as a pilot sample. Varying concentrations of strontium and lanthanum were added to solutions of the ashed pilot sample for the determination of calcium and magnesium using flame atomic absorption spectrophotometry operated on the air-acetylene mode. At least 3000 ppm of strontium or lanthanum was required to completely overcome the interference of phosphate ion, PO(4)(3-), and give peak values for calcium. The presence of strontium or lanthanum did not affect the amount of magnesium obtained from the analyses. Based on this, a procedure is proposed and the results obtained by this procedure for calcium are more enhanced than those obtained without the addition of strontium or lanthanum for the same samples whereas comparable results were obtained for all other elements whether strontium or lanthanum was added or not. The method gives more accurate results and is reproducible. The coefficients of variation calculated using one of the samples were 0.58% for magnesium, 3.12% for zinc; 0.44% for calcium, 11.06% for lead, 22.22% for nickel, 3.53% for manganese and 3.50% for iron at the concentration levels found in that sample. Recoveries of spiked calcium, magnesium and zinc were quantitative. Also, for selected elements, results from the procedure compared well with those from chemical analysis. | 18,968,034 |
Radiosensitivity study of cefazolin sodium. | The extent of physico-chemical changes induced by irradiation of cefazolin sodium was investigated. The methods used were potency determination, impurity profile, colour measurements and pH measurements. The potency of irradiated samples at 25 kGy was 4+/-2% lower than that of the non irradiated ones. The total amount of related substances increased from 0.72+/-0.01% in the non irradiated samples to 4.9+/-0.7% in the samples irradiated at 25 kGy. Most of the peaks showed trace amounts (<0.01%), the largest one represented 1.2+/-0.5% of the total related substances. Only two peaks were identified by chromatography: the methyl-1,2,3-thiazol-2 thiol-5 and the 7-aminocephalosporanic acid. The latter related substance is only produced by the irradiation of cefazolin sodium. The pH values of the samples were within the specifications of the European Pharmacopoeia. The colour of the cefazolin sodium powder changed from white to yellow upon irradiation. The yellow colour persisted after the dissolution of the powder. Most of the tests carried out met the Pharmacopoeia's specifications, except the one concerning the colour of the solution. | 18,968,047 |
Conductometric determination of carbon in uranium carbide and its solution in nitric acid. | A simple but accurate method has been developed for the determination of carbon in uranium carbide powders/pellets as well as in solutions of uranyl nitrates. The methodology involves quantitative conversion of carbon present in the sample to carbon dioxide that is subsequently absorbed in a dilute solution of barium hydroxide. The conductivity shift of the barium hydroxide solution is monitored on-line continuously using a laboratory-built PC-based conductivity measurement system that has been developed in-house based on the direct conversion of conductance to the digital pulse frequency. A new gas absorption cell has been designed to ensure quantitative absorption during the residence time of the gas in the cell. The method is sensitive, accurate and precise to 1-3% at 600-1000 mug of carbon in samples of uranium carbide. | 18,968,049 |
A long path length spectroelectrochemical behavior analysis of the coabsorption system. | The coabsorption system in which both species Red and Ox absorb at the same wavelength was investigated by the long path length spectroelectrochemical technique. The variation of the system absorbance at the isosbestic point with time, which is strongly dependent upon the diffusion coefficients and their difference, was calculated by employing the method of digital simulation under semi-infinite condition. Simulated results indicated that each A(t)-t curve corresponded to definite values of D(R) and D(O) on the condition that D(R) is not equal to D(O). The species diffusion coefficients were evaluated by comparing the spectroelectrochemical experimental result at the isosbestic point with the simulated result, and experimentally verified by the study of electrooxidation of hydroquinone. | 18,968,051 |
The role of manganese(IV) compounds as oxidants - a review. | A historical review of the development of manganese(IV) chemistry and its application in analytical chemistry is presented. A brief presentation of the presence and importance of manganese(IV) in other areas of chemistry is also given. | 18,968,056 |
Determination of trace metal ions by AAS in natural water samples after preconcentration of pyrocatechol violet complexes on an activated carbon column. | A simple preconcentration method is described for the determination of Cu, Mn, Co, Cd, Pb, Ni and Cr in water samples by flame AAS. Trace metal ions in water were sorbed as pyrocatechol violet complexes on activated carbon column at the pH range of 4-8, then eluted with 1 M HNO(3) in acetone. The effect of major cations and anions of the natural water samples on the sorption of metal ions has been also investigated. The concentration of the metal ions detected after preconcentration was in agreement with the added amount. The present method was found to be applicable to the preconcentration of Cu, Mn, Co, Cd, Pb, Ni and Cr in natural water samples with good results such as R.S.D. from 3 to 8% (N=10) and detection limits under 70 ng l(-1). | 18,968,065 |
Oxidation at a sol-gel composite electrode doped with a dirhodium-substituted polyoxometalate for amperometric detection of peptides separated by HPLC. | Oxidation of a variety of compounds, including methionine (Met), using a complex formed between dirhodium(II) acetate and the lacunary form of phosphotungstic acid as the catalyst is effective over a wide range of conditions, including pH 2-10. Thus, amperometric detection at a composite in which this complex is immobilized in a sol-gel material does not place restrictions on selection of conditions for separations by reverse-phase HPLC. A demonstration of this point is shown by a study of Met, Met-Phe, Phe-Met, Met-Met, and Gly-Met-Gly (Phe, phenylalanine; Gly, glycine). Using a 0.05 M phosphate buffer at pH 6.7, a C18 column, and a flow rate of 1 ml min(-1), capacity factors for Met, Gly-Met-Gly, Met-Met, and Phe-Met were 1.4, 2.1, 5.6, and 34, respectively. Phe-Met and Met-Phe co-eluted. | 18,968,070 |
Effect of concentration of ion exchanger, plasticizer and molecular weight of cyanocopolymers on selectivity and sensitivity of Cd(II) ion selective electrode. | Potential response of cadmium(II) ion selective electrode based on cyanocopolymer matrices and 8-hydroxyquinoline as ionophore has been evaluated by varying the amount of ionophore, plasticizer and the molecular weight of the cyanocopolymer. The sensitivity, working range, response time, and metal ions interference have shown a significant dependence on the concentration of ionophore, plasticizer and molecular weight of cyanocopolymers. The electrodes prepared with 2.38x10(-2) mol kg(-1) of ionophore, 1.23x10(-2) mol dm(-3) of plasticizer and 2.0 g of cyanocopolymer (molecular wt., 59 365) have shown a Nernstian slope of 29.00+/-0.001 mV per decade activities of Cd(2+) ions with a response time of 12+/-0.007 s. Electrodes have shown an appreciable selectivity for Cd(2+) ions in the presence of alkali and alkaline earth metal ions and could be used in a pH range of 2.5-6.5. The cyano groups of the copolymers contributed significantly to enhance the selectivity of the electrode. The electrode has shown an appreciable average life of 6 months without any significant drift in the electrode potential and found to be free from leaching of membrane ingredients. Electrode response is explained considering phase boundary model based on thermodynamic considerations. | 18,968,071 |
Determination of clenbuterol in pharmaceutical preparations by reaction with o-phthalaldehyde using a flow-injection fluorimetric procedure. | A new procedure for the determination of clenbuterol is proposed using flow-injection and fluorimetric detection. The method is based on the derivatization reaction of the primary amine group with o-phthalaldehyde in the presence of 2-mercaptoethanol. The calibration graph based on peak area was linear in the range 0.2-5 mug ml(-1) and the detection limit was 0.06 mug ml(-1). The method was validated using a reference spectrophotometric procedure and was applied to the determination of the drug in commercial pharmaceutical preparations. | 18,968,087 |
Isolation and structural characterization of a pectin homo and ramnogalacturonan. | With a purpose to achieve an individual components of the pectins there was purified and separated the acidic components of the apple pectin and its chemical structure was studied using (13)C-NMR-Spectroscopy. The apple pectin was consecutively subjected to processing with hydrochloric acid and ethanol mixture, ultracentrifuging at 7000 and 40 000 rpm, ultrafiltration, fractionation on cellulose (DEAE-52) ion exchanger, eluting by the phosphate buffer. The contents of the acidic and neutral polysaccharides in an initial pectin and in the selected fractions controlled by narrow-band filter - spectroscopically in relation to E(q)=E(298)/E(315). In the (13)C-NMR-spectrums of the pectins before purifications on the ion exchanges besides the signals characteristic for homogalacturon, resonances are observed at 105.8, 79.01, 76.3, 73.9, 70.0 and 18.32 m.d., appropriate to the ramnogalacturonan residues. Resonance lines of acidic fraction in the field of 69.8, 70.6, 72.3, 80.6, 100.6 and 176.6 m.d. are referred to homogalacturonan residues and signals at 55.9, 73.3, 80.8, 101.6 and 172.6 m.d. to their methoxyl group. Minor resonance at 18.32 originated from C-6 rhamnose residues, substituted or unsubsituted with galactosyl-chains. Hence it has been shown that the apple pectin consist mainly of linear homogalacturonan and branched ramnogalacturonan macromolecules. | 18,968,102 |
Simultaneous derivative spectrophotometric determination of cobalt(II) and nickel(II) by dithizone without extraction. | Dithizone (Dz), a common extractive-photometric ligand for Co(II) and Ni(II), has been dissolved in the water-miscible solvent tetrahydrofurane (THF) so as to constitute a reagent for both metals in aqueous phase without extraction. Complex formation was complete for both metals at pH 12.0 (adjusted by aqueous NH(3)) within 30 min, and the complexes were stable for at least 2 h. First-derivative spectra of the metal dithizonates (singly or as binary mixtures) were preferred to ordinary spectra, because working wavelength determination was more precise and spectral overlap was less. Two wavelengths at which the spectral overlap was minimum were selected as analytical wavelengths, i.e. 620 nm for Co and 740 nm for Ni, and the calibration curves drawn with zero-to-peak values as a function of concentration were linear for these wavelengths. Thus, the total (1)D values at 620 and 740 nm of the mixtures were used to determine Co and Ni concentrations. The relative standard deviation (R.S.D.) for the analysis of Co (3.0 mg l(-1)) individually was 3.5%, and for its admixture with Ni (3.5 mg l(-1)) was 2.5%. The R.S.D. for the analysis of Ni (5.9 mg l(-1)) individually and for its admixture with Co (1.8 mg l(-1)) were 5.5 and 5.8%, respectively. The linear range in (1)D evaluation was between 5.0x10(-6) and 1.0x10(-4) M for Co and 2.0x10(-5)-2.0x10(-4) M for Ni. Interference analysis was performed for individual metal (Co or Ni) determinations. Finally, the method has been applied to a Ni-Cr-based dental alloy (Wiron 99) successfully. | 18,968,111 |
Coulometric detector based on porous carbon felt working electrode for flow injection analysis. | A coulometric detector based on carbon felt as working electrode has been designed. Ascorbic acid, hydroquinone, gallic acid and sulfur dioxide were used as electroactive compounds to determine the electrochemical characteristics of this detector. The coulometric conversion efficiency, selectivity, linear response range, detection limit and mass transfer coefficient were investigated in order to use the detector as a cleanup device in a flow injection system with dual-detector. This system has been used for determination of sulfur dioxide in wine, and the results are compared to those from the aspiration-oxidation method. | 18,968,153 |
Ensuring complete absence of Ce(IV) and measurement of the stability constant of the fluoride complex of Ce(III). | Literature survey revealed a wide variation in the measured stability constant values of the aqueous fluoride complexes of trivalent cerium. This could be due to inadequate care for full conversion and maintenance of the oxidation state of cerium to trivalent state. In the present work quinhydrone has been used to ensure complete absence of Ce(IV) and the stability constant of CeF(2+) in 1 M NaClO(4) has been measured potentiometrically using a fluoride ion selective electrode. Log beta(1) obtained in this work was 2.936+/-0.024 and fitted well with the general trend of stability constants of the lanthanide (rare earths) fluorides in aqueous solution. | 18,968,159 |
Construction and evaluation of ion selective electrodes for nitrate with a summing operational amplifier. Application to tobacco analysis. | In this paper, the construction and evaluation of an electrode selective to nitrate with improved sensitivity, constructed like a conventional electrode (ISE) but using an operational amplifier to sum the potentials supplied by four membranes (ESOA) is described. The two types of electrodes, without an inner reference solution, were constructed using tetraoctylammonium bromide as sensor, dibutylphthalate as solvent mediator and PVC as plastic matrix, the membranes obtained directly applied onto a conductive epoxy resin support. After the comparative evaluation of their working characteristics they were used in the determination of nitrate in different types of tobacco. The limit of detection of the direct potentiometric method developed was found to be 0.18 g kg(-1) and the precision and accuracy of the method, when applied to eight different samples of tobacco, expressed in terms of mean R.S.D. and average percentage of spike recovery was 0.6 and 100.3%, respectively. The comparison of variances showed, on all ocassions, that the results obtained by the ESOA were similar to those obtained by the conventional ISE, but with higher precision. Linear regression analysis showed good agreement (r=0.9994) between the results obtained by the developed potentiometric method and those of a spectrophotometric method based on brucine, adopted as reference method, when applied simultaneously to 32 samples of different types of tobacco. | 18,968,163 |
Room-temperature phosphorescence of 6-bromo-2-naphthol included in beta-cyclodextrin in the presence of cyclohexane. | The formation constant for a 1:1 binary complex between 6-bromo-2-naphthol (6B2N) and beta-cyclodextrin (CD) in aqueous solution was determined by both absorptimetric and fluorimetric methods. Room-temperature phosphorescence (RTP) was induced by adding small amounts of different apolar liquids as the third component, with cyclohexane producing the strongest enhancement effect. Microcrystals formed in the ternary system seem to be necessary for obtaining phosphorescence emission. The deoxygenation by flowing nitrogen does not improve the RTP signals, while the addition of sodium sulfite as chemical deoxygenant produces quenching of the signals. The calibration graph for 6-bromo-2-naphthol in the presence of beta-CD and cyclohexane was linear for the range of concentrations between 0.04 and 1 mug ml(-1), with a detection limit of 0.04 mug ml(-1). | 18,968,175 |
Chemiluminescence determination of some fluoroquinolone derivatives in pharmaceutical formulations and biological fluids using [Ru(bipy)(3)(2+)]-Ce(IV) system. | A new chemiluminescence (CL) method using flow injection has been described for the rapid and sensitive determination of three fluoroquinolone derivatives, namely ofloxacin, norfloxacin and ciprofloxacin hydrochloride. The method is based on the CL reaction of the studied fluoroquinolones with tris(2,2'-bipyridyl)ruthenium(II) [Ru(bipy)(3)(2+)] and Ce(IV) in sulfuric acid medium. Under the optimum conditions, the CL intensity is proportional to the concentration of the drugs in solution over the range 0.05-7.0 mug ml(-1) for norfloxacin, 0.05-6.0 mug ml(-1) for ciprofloxacin hydrochloride and 0.003-0.7 mug ml(-1) for ofloxacin. The limits of detection (s/n=3) were 3.1x10(-8) M norfloxacin, 2.6x10(-8) M ciprofloxacin hydrochloride and 5.5x10(-9) M ofloxacin. The method was applied successfully to the determination of these compounds in dosage forms and biological fluids. | 18,968,179 |
Synthesis of a novel chemiluminescent reagent for the determination of hydrogen peroxide in snow waters. | 7-(4,6-Dichloro-1,3,5-triazinylamino)-4-methylcoumarin (DTMC) was synthesized as a completely new chemiluminescent reagent, and with it a novel chemiluminescence method was developed for the determination of hydrogen peroxide in the absence of any added catalyst or co-oxidant. The chemiluminescence intensity of the DTMC-H(2)O(2) system could be enhanced by the addition of cation surfactants. The chemiluminescence intensity was directly proportional to the concentration of H(2)O(2) in the range 1.0 x 10(-7)-4.0x10(-4) mol l(-1), and the detection limit was 4.0 x 10(-8) mol l(-1). The relative S.D. was 4.9% for 1.0 x 10(-6) mol l(-1) of H(2)O(2) (n=10). The selectivity of this method was high, and most of the transition metal ions have no effect on the determination. The proposed method has been applied to the determination of trace amounts of hydrogen peroxide in snow water. A possible mechanism of the chemiluminescence reaction is also discussed. | 18,968,188 |
Determination of the herbicide desmetryne in organised media by adsorptive stripping voltammetry. | An electroanalytical method for the determination of the herbicide desmetryne at nanomolar levels in dispersed media, based on adsorptive stripping voltammetry, is reported. The adsorption of desmetryne at the hanging mercury drop electrode was checked both in micellar solutions, where the anionic surfactant sodium pentanesulphonate was chosen as the most suitable surfactant agent, and in oil-in-water emulsions prepared with ethyl acetate as the organic solvent. In a micellar medium formed with 0.02% sodium pentanesulphonate and with 0.1 mol l(-1) Britton-Robinson buffer (pH 1.5), the herbicide could be determined over the 1.0 x 10(-8)-4.0 x 10(-7) mol l(-1) concentration range, when an accumulation potential of -0.70 V was applied for 50 s. On the other hand, in an oil-in-water emulsion formed with 2% ethyl acetate and 0.04% sodium pentanesulphonate as emulsifying agent in 0.1 mol l(-1) HClO(4), desmetryne could be determined over the 2.0 x 10(-9)-1.0 x 10(-7) mol l(-1) concentration range. The limits of detection were 2.4 x 10(-9) and 4.2 x 10(-10) mol l(-1) in micellar and emulsified media, respectively, with R.S.D.s (n=10) 3.6 and 3.7%. The degree of interference from some other s-triazines on the desmetryne differential pulse response was also evaluated. Finally, the method developed in emulsified medium was applied to the determination of desmetryne in spiked apple juice. | 18,968,189 |
Influence of pH and fluoride concentration on titanium passivating layer: stability of titanium dioxide. | Titanium and titanium alloy biomaterials are considered as being corrosion resistant, because of the formation of a titanium oxide passivating layer, which is not easily soluble even in acid media. In odontology, using dental preparations containing fluorides could alter the behaviour of titanium. After a review of the experimental works dealing with the effects of fluoride ions at different pH on titanium salts in solution, it was proceeded to a thermodynamic investigation at 25 degrees C in the range of concentrations and pH corresponding to the solutions commonly used. Such a study gives a possibility to specify which species could be involved in the corrosion reaction to calculate the corresponding potentials, and lastly to define the domain of insolubility of TiO(2). From these results, the reaction of titanium in laboratory spontaneous corrosion and voltammetric experiments was interpreted. From the recent experiments described and discussed in this article, it becomes evident that the close connection with the results obtained in this study contributes to support our thermodynamic model. | 18,968,197 |
Effect of structural modifications of diaza-18-crown-6 on the extractability and selectivity of univalent metal picrates. | The solvent extraction of univalent metal cations with N,N'-dibenzyl-1,4,10,13-tetraoxa-7,16 diaza-2,3,11,12-dibenzocycloocta deca-2,11-diene (L(1)), N,N' didodecyl-1,4,10,13-tetraoxa-7,16-diaza-2,3-benzocylooctadeca-2 ene (L(2)) and N,N'-dibenzyl-1,4,10,13-tetraoxa-7,16 diaza-2,3,11,12-dibenzocyclo octadeca-2,11-diene (L(3)) with picrate anion into dichloromethane has been studied at 25 degrees C by UV-visible spectroscopy. The extractability and selectivity of univalent metal picrates (Li(+), Na(+), Ag(+), PhCH(2)NH(3)(+), NH(4)(+)) was evaluated as a function of [ligand]/[metal cation]. L(2) showed the highest extractability and selectivity for Li(+) over the larger studied cations, and also exhibited the highest [Li(+)]/[NH(4)(+)] selectivity as L/M=1. | 18,968,200 |
Electrochemical detection of thiols in biological media. | The utilisation of catechol as an electrochemical indicator for the presence of sulphydryl thiols (RSH) has been investigated. The electrochemical oxidation of the catechol within tissue culture media was examined with the influence exerted on the redox chemistry by cysteine evaluated in terms of the development of an analytical protocol. The electro-generation of o-quinone was found to be followed by a 1,4-addition reaction with available cysteine such that an increase in the current, attributed to the re-oxidation of the thiol-catechol adduct, could be exploited as means of quantifying the concentration of the thiol. The selectivity of the reaction has been assessed with no interference from lysine, tyrosine, methionine or cystine. Other amino acids possessing sulphydryl thiol functionalities (homocysteine and glutathione) were, however, found to react through a similar route to that observed with cysteine. | 18,968,201 |
Preconcentration of traces of gold, silver and palladium on activated carbon and its determination in geological samples by flame AAS after wet ashing. | A simple, rapid and cost effective preconcentration method is described for the determination of traces of gold (Au), silver (Ag) and palladium (Pd) in geological samples by flame atomic absorption spectrophotometry (AAS). The method is based on sorption of analytes (Au, Ag and Pd) on powdered activated carbon (AC) at pH approximately 1 in hydrochloric acid (HCl) medium. The samples are decomposed by aqua regia - HCl treatment. The quantitative sorption (better than 92%) of analytes is obtained on AC (in absence of complexing agent), by simply manipulating optimal conditions. The unique feature of the method is, the analytes are recovered quantitatively from AC by oxidizing and completely solubilising the carbon using concentrated nitric acid (HNO(3)) and perchloric acid (HClO(4)) i.e. by wet ashing. The method of wet ashing has several advantages over conventional dry ashing. The accuracy of the method is evaluated by analysing, five Canada centre for mineral and energy technology (CANMET) standards; MA-3, MA-1b, FER-1, SU-1A, and CPB-1. In addition, ASK-3 and one inhouse standard, kolar gold field (KGF) samples was also analysed. As no standard for Pd is available, its accuracy was evaluated by standard addition method. The method was applied on numerous geological samples for the determination of Au, Ag and Pd down to 0.1 ppm (based on 10 g sample) within +/-10% R.S.D. (n=5). The method could easily be adopted by any laboratory as the inputs are minimal (AC), inexpensive and easily available. | 18,968,206 |
Flow injection spectrophotometric analysis of lead in human saliva for monitoring environmental pollution. | A new highly sensitive, simple and low-cost methodology for the direct determination of Pb (II) with 2-(5-bromo-2-pyridylazo)-5-dimethylaminophenol in ethanolic medium has been developed. The absorption spectroscopy of the complex has been examined in detail, and the chemical variables affecting the sensitivity of procedure studied, optimized and applied to the determination of trace amounts of lead in human saliva. Under the optimal experimental conditions, a precision of 1.61x10(-4) mug cm(-2) was achieved, the molar absorptivity being (epsilon) 5.6x10(4) l mol(-1) cm(-1). An FI technique is proposed, and it is possible to determine trace levels of lead by injection into a steam buffered at pH 7.15, containing 70% ethanol: 30% Tris buffer 3.5x10(-3) mol l(-1) (pH=7.2), 1x10(-4) mol l(-1) 5-BrDMPAP. The FIA configuration allows the analysis of 45 samples per hour. The lower limit of detection (LOD) was 1x10(-7) mol l(-1). The calibration plot was linear at least within two orders of magnitude of lead concentration. The use of an HPLC pump for the FI analysis led to a substantial improvement in the analytical performance of the method, which clearly satisfies the typical requirements for control processes. | 18,968,224 |
On the possibility to improve the performance of flow injection analysis by deconvolution of spectrophotometric data. | The concentration profile of chemical species pumped through a tubular system of 0.5-mm inner diameter is found to be trapezial shaped, as described theoretically by including the spatial resolution of the instrument, friction and diffusion. By applying the theory, which is based on the concept of segment flow, to experiments, it is shown that an injected segment of solute is diluted predominantly at the front and at the tail proportion of the segment in motion. A double-peaked structure in experiments of flow-injection analysis (FIA) was identified and by including all the data of the experimentally measured responses, it was possible to obtain an improvement of the sensitivity by a factor of 22 and obtain almost a factor of three times improvement on the standard deviation. | 18,968,234 |
Electrothermal atomic absorption spectrometric determination of cobalt, copper, lead and nickel traces in aragonite following flotation and extraction separation. | A method of determination of Co, Cu, Pb and Ni in nanogram quantities from aragonite is presented. Flotation and extraction of Co, Cu, Pb and Ni is suggested as methods for elimination matrix interferences of calcium. The method of flotation is performed by iron(III) hexamethylenedithiocarbamate, Fe(HMDTC)(3), as a colloid precipitate collector. The liquid-liquid extraction of Co, Cu, Pb and Ni is carried out by sodium diethyldithiocarbamate, NaDDTC, as complexing reagent into methylisobutyl ketone, MIBK. The electrothermal atomic absorption spectrometry (ETAAS) is used for determination of analytes. The detection limits of ETAAS followed by flotation are: 7.8 ng.g(-1) for Co, 17.1 ng.g(-1) for Cu, 7.2 ng.g(-1) for Pb and 9.0 mug.g(-1) for Ni. The detection limits of ETAAS followed by extraction are found to be: 12.0 ng.g(-1) for Co, 51.0 ng.g(-1) for Cu, 24.0 ng.g(-1) for Pb and 21.0 ng.g(-1) for Ni. | 18,968,235 |
Determination of ketorolac in human serum by square wave adsorptive stripping voltammetry. | The adsorption behavior of ketorolac on a hanging mercury drop electrode (HMDE) was explored by square-wave and cyclic voltammetry. The square wave voltammetric response of ketorolac depends on the parameters of the square wave voltammetry excitation signal as well as on the pH of the medium and the accumulation time. The drug was accumulated at HMDE and a well-defined peak was obtained at -1.41 V versus. Ag/AgCl (saturated KCl) in acetate buffer of pH 5.0. A square-wave adsorptive stripping voltammetric method for the quantitative determination of ketorolac was developed. The linear concentration range was 1x10(-10)-1x10(-8) when using 300 s accumulation at -0.8 V. The detection limit of ketorolac was 1.0x10 (-11)M . The precision was excellent with relative standard deviation of 3.85% at concentration of 5x10 (-8)M after 60 s accumulation time. Applicability to serum samples was illustrated. A detection limit of 14 ng per ml of serum was obtained. | 18,968,250 |
A study on the interaction between concanavalin A and glycogen by light scattering technique and its analytical application. | The mixture of concanavalin A (Con A) and glycogen shows strong light scattering character. Based on it, the interaction between Con A and glycogen was studied on a common spectrofluorimeter by light scattering technique. Many factors affecting the light scattering intensity (LSI), such as pH, temperature, reaction time, ion strength and the denaturing agent of protein were studied in detail. Experimental results showed that the LSI reached its maximum after mixing Con A with glycogen for about 20 min in pH 7.4 Tris-HCl buffer at 37 degrees C. The results also suggested that the conformation of Con A was critical for its unique binding affinity to glycogen. Electrostatic forces should not be the primary interaction between glycogen and Con A. Under proper experimental conditions, the determination method for glycogen by light scattering technique was developed. The glycogen determination can be performed in the range of 0.48-32.0, 0.50-32.0 and 0.32-24.0 mug/ml for Rabbit liver glycogen (RL Gly), Oyster glycogen (O Gly) and Clam Glycogen (C Gly), respectively. The influence of co-existing substances such as proteins, mono- and di-saccharides and metal ions was evaluated, and little interference came from the foreign substances. The determinations of glycogen in synthetic samples demonstrated that the recovery rate was in the range of 98.1-103% and the relative standard deviations (RSD) were lower than 5.0%. | 18,968,256 |
New method for separation and determination of denatured caseins by hydrophobic interaction chromatography. | A new method for the separation of denatured alpha-, beta- and kappa- caseins by hydrophobic interaction chromatography (HIC) is proposed. The method is based on an easy solubilization of commercial and real samples by 4.0 M guanidine thiocyanate (GdmSCN) and elution on a TSK-Gel(R) Phenyl-5PW column (TosoHaas) in the presence of 8.0 M urea in the mobile phase. The procedure, applied to commercial caseins and to real, raw samples (whole milk powder and fat-free yoghurt) is not expensive, it requires common high performance liquid chromatography (HPLC) instrumentation and allows the separation of caseins also in the presence of whey proteins. Quantitative results on the analysis of alpha-, beta- and kappa-caseins in real samples are also reported. | 18,968,257 |
An insight into the solution equilibria of magnesium(II) with purpurin and spectrophotometric determination of magnesium. | The complexation equilibria of magnesium(II) with purpurin (PURP) are studied spectrophotometrically as a function of pH in 50% (v/v) ethanol-water medium at 20 degrees C. The uncharged complex formed at pH 9.5 allows precise and accurate determination of magnesium over the concentration range 0.8-4.3 mug ml(-1). The molar absorptivity of the Mg-PURP complex at 540 nm and detection limit for Mg are 9.2x10(3) l mol(-1) cm(-1) and 75 ng ml(-1), respectively. The proposed method is rapid and possesses reasonable selectivity. Under the optimum conditions, the use of first-derivative spectrophotometry has the advantage of high sensitivity than normal spectrophotometry and allows the determination of 0.2 mug ml(-1) of magnesium. The validity of the method is examined by analysing several SRM Portland cement samples and a variety of cement materials of variable magnesia content. | 18,968,260 |
Redox-potentiometric determination of peroxide value in edible oils without titration. | Standard methods for peroxide value determination in edible oils, which are based on KI oxidation by the hydroperoxides and volumetric titration of the liberated iodine, have been improved using redox-potentiometric iodine determination without titration. Stages of the KI oxidation and redox-potentiometric measurements were combined in the same electrochemical cell. The limit of quantitation of the new method is 0.16 meq kg(-1), which allows the analysis of fresh refined oils. The method is simple, not time and labor consuming, and suitable for automation. | 18,968,266 |
Screening people for illicit substances: a survey of current portal technology. | The need to implement more effective, cost efficient, non-intrusive ways of screening people for concealed drugs, explosives and weapons is a major security initiative for the U.S. and elsewhere. A new generation of portals suitable for security checkpoints is under development. These will be able to find contraband with high probabilities of detection, and low false-alarm rates. Some portals image the body using either low dose X-rays or millimeter wave interrogation, and analyze the radiation back-scattered from the body, providing images of concealed objects. Other portals operate essentially as anomaly detectors, finding objects on the human body. A series of portals is also under development that can harvest and analyze vapors or particles of the contraband substances. Some of the issues surrounding portal development include perceived safety issues, privacy issues, and operational issues such as ease of operation, non-invasiveness, and ease of interpretation. It is believed that portal technology will mature, and the cost of portals will fall sufficiently to make widespread deployment of portals at security checkpoints a reality within the next decade. | 18,968,270 |
Selective dissolution and one step separation of terpene trilactones in ginkgo leaf extracts for GC-FID determination. | Under ultrasonication, the ginkgo terpene trilactones, ginkgolides and bilobalide, in ginkgo extracts can be selectively dissolved in 10% aqueous NaH(2)PO(4) solution at a temperature of 50-60 degrees C and separated from the solution by extraction with a mixture of ethyl acetate/tetrahydrofuran in a capped vial. After derivatization, these terpene trilactones can be quantified using GC-FID. This method has a detection limit of 10 ng, and the RSD was 6% (n=5). Twelve commercial GBE products in powder, liquid, tablet and capsule forms were analyzed. The total time required for analyzing these samples from sample preparation to final data processing was less than 6 h, and the total organic solvent consumption was less than 40 ml. This procedure proves to be a simple, fast, safe, and effective method for all types of Ginkgo biloba extracts (GBE) including the "complex" or "advanced" formulas. | 18,968,289 |
Effects of fungal laccase immobilization procedures for the development of a biosensor for phenol compounds. | Fungal laccase was immobilized on carbon-fiber electrodes using classical methods: physical adsorption, glutaraldehyde, carbodiimide and carbodiimide/glutaraldehyde. The highest biosensor response was obtained using carbodiimide/glutaraldehyde for coupling laccase to carboxyl groups on the carbon fibers. In this method, different percentages of glutaraldehyde had important effects on the sensitivity of the biosensor, the best percentage of glutaraldehyde being 10% (m/v). The behavior of the obtained biosensor was investigated in terms of sensitivity, operational range, pH and applied potential. The developed biosensor showed an optimum response at pH 5.0 and at an applied potential of -100 mV. The immobilized laccase retained a good activity for over 2 months. | 18,968,290 |
Application of the H-point standard addition method to the speciation of Fe(II) and Fe(III) with chromogenic mixed reagents. | Simultaneous determination of Fe(II) and Fe(III) or selective determination of each oxidation state of iron in the presence of the other one by H-point standard addition method (HPSAM) is described. Mixed reagents of 1,10-phenanthroline and salicylic acid was used as a selective chromogenic system for speciation of Fe(II) and Fe(III). It was shown that with appropriate selection of wavelength pairs, both Fe(II) and Fe(III) can be considered as analyte. The results showed that Fe(II) and Fe(III) can be determined simultaneously with the concentration ratios of Fe(II) to Fe(III) varying from 10:1 to 1:20 in the mixed sample. The accuracy and precision of the method are all satisfactory. | 18,968,295 |
Urea biosensor based on amperometric pH-sensing with hematein as a pH-sensitive redox mediator. | The natural dye hematein in water solution was used as a pH-sensitive redox-active mediator for amperometric pH-sensing. The electrochemical characteristics were studied using cyclic voltammetry and chronoamperometry. Several types of urea biosensors were constructed with urease on the surface of platinum and graphite composite electrodes or in the bulk of the graphite composite. They were used for the amperometric urea determination at a working potential of 0 mV (versus SCE) using 0.5 mM hematein. Detection limits and response linearity was in the micromolar range depending on the biosensor type, concentration and pH of buffers used. An interference study of various cations, anions, and substances, which may be present in real samples demonstrated good selectivity for the determination of urea. The biosensors showed good operational (>3 h) and storage (>3 months) stability. The results of urea determination in blood and urine obtained by biosensor correlated well with those obtained by a spectrophotometric reference method. | 18,968,299 |
PVC membrane based potentiometric sensors for uranium determination. | Two novel uranyl PVC matrix membrane sensors responsive to uranyl ion are described. The first sensor incorporates tris(2-ethylhexyl)phosphate (TEHP) as both electroactive material and plasticizer and sodium tetraphenylborate (NaTPB) as an ion discriminator. The sensor displays a rapid and linear response for UO(2)(2+) ions over the concentration range 1x10(-1)-2x10(-5) mol l(-1) UO(2)(2+) with a cationic slope of 25.0+/-0.2 mV decade(-1). The working pH range is 2.8-3.6 and the life span is 4 weeks. The second sensor contains O-(1,2-dihydro-2-oxo-1-pyridyl)-N,N,N',N'-bis(tetra-methylene)uronium hexafluorophosphate (TPTU) as a sensing material, sodium tetraphenylborate as an ion discriminator and dioctyl phenylphosphonate (DOPP) as a plasticizer. Linear and stable response for 1x10(-1)-5x10(-5) mol l(-1) UO(2)(2+) with near-Nernstian slope of 27.5+/-0.2 mV decade(-1) are obtained. The working pH range is 2.5-3.5 and the life span of the sensor is 6 weeks. Interference from many inorganic cations is negligible for both sensors. However, interference caused by some ions (e.g. Th(4+), Cu(2+), Fe(3+)) is eliminated by a prior ion exchange or solvent extraction step. Direct potentiometric determination of as little as 5 mug ml(-1) uranium in aqueous solutions shows an average recovery of 97.2+/-1.3%. Application for the determination of uranium at levels of 0.01-1 wt.% in naturally occurring and certified ores gives results with good correlation with data obtained by X-ray fluorescence. | 18,968,336 |
The study of PVP/Pd/IrO(2) modified sensor for amperometric determination of sulfur dioxide. | A novel electrochemical sensor for the detection of sulfur dioxide in both gas and solution is described. The chemically modified electrode was constructed by polymerizing (4-VP), palladium and iridium oxide (PVP/Pd/IrO(2)) onto a platinum microelectrode which exhibits excellent catalytic activity toward sulfite with an oxidation potential of +0.50 V. The SO(2) gas sensor is based on the PVP/Pd/IrO(2) modified electrode as working electrode, Ag/AgCl electrode as reference electrode, Pt electrode as counter electrode and a porous film, which is in direct contact with the gas-containing atmosphere. The effect of different internal electrolyte solutions of hydrochloric acid, sulfuric acid, phosphates buffer solution, mixed solution of dimethyl sulfoxide and sulfuric acid to the determination of SO(2) was also studied. The sensor was found to have a high current sensitivity, a short response time and a good reproducibility for the detection of SO(2). It has good potential to be used in the field of environmental monitoring and controlling. | 18,968,366 |
A simple vapour phase decomposition (VPD) of quartz powder in a polypropylene vessel and determination of phosphorus by spectrophotometry. | A simple, low pressure, low temperature vapour phase decomposition (VPD) of quartz powder has been developed for the determination of phosphorus. A platinum dish containing the quartz or silicon powder was placed inside a polypropylene vessel containing 40 ml of 1:1 mixture of HF and HNO(3). After capping the vessel, the entire assembly was heated on a water bath at approximately 90 degrees C for 8 h. The platinum dish was removed from the vessel, the sample solution was treated with 0.5 ml of H(2)SO(4) and 0.5 ml of HClO(4) and was heated on a hot plate till HClO(4) fumed out. The resultant solution was diluted to 40 ml ( approximately 0.4N), analysed for phosphorus by spectrophotometry as an ion-pair of molybdophosphate with crystal violet. Phosphorus contamination by reagents has been drastically reduced (around 250 times) compared to the conventional dissolution procedure. The optimum reaction conditions were [H(+)]=0.42N, [H(+)]/Mo=62 for the formation of molybdophosphate and its extraction into n-butyl acetate. No interferences due to fluoride, silicate (active silica) and arsenic (V) upto 6.7x10(3),2.7x10(3) and 2.0x10(3) times the content of phosphorus, respectively were observed. The LOD was found to be 0.066 mug g(-1) (+/-3 s). RSD is 0.4-2.3% and the molar absorptivity is 2.7x10(5) l mole(-1) cm(-1). | 18,968,395 |
Analysis of selenium species by capillary electrophoresis. | The presence of selenium in the form of different species in environmental and biological samples receives an increasing attention due to better understanding of its bioavailability, toxicity and transport mechanism. For many years, gas and liquid chromatography have been extensively explored in speciation analysis of this element. Recently, capillary electrophoresis (CE) has made much progress in this field. This review presents the developments in the application of CE for simultaneous separation and determination of different selenium compounds. Various separation approaches and detection methods as well as pre-concentration techniques are discussed. The speciation performance of CE is illustrated by a number of practically relevant applications. | 18,968,412 |
Determination for micro amounts of nucleic acids by a resonance light scattering technique with dequalinium chloride. | Based on the strong enhancement effect of nucleic acids on resonance light scattering of dequalinium chloride, the determination method for micro amounts of nucleic acids has been developed. Under the experimental conditions (5.0x10(-5) mol l(-1) dequalinium, pH 7.0, at room temperature) the linear range of this assay is 0.04-10.0 mug ml(-1) for calf thymus DNA and fish sperm DNA, and 0.04-35.0 mug ml(-1) for yeast RNA. The detection limits (3sigma) are 6.2 ng ml(-1) for calf thymus DNA, 7.4 ng ml(-1) for fish sperm DNA, and 7.0 ng ml(-1) for yeast RNA, respectively. Almost no interference can be observed from ionic strength, proteins, nucleoside, and most of the metal ions. Six synthetic samples were determined satisfactorily. | 18,968,413 |
Comparisons of sorption of aquatic humic matter by DAX-8 and XAD-8 resins from solid-state (13)C NMR spectroscopy's point of view. | Aquatic humic solutes were separated in parallel by the non-ionic macroporous DAX-8 and XAD-8 resins from four different fresh water sources. On average, the sorptive power of the DAX-8 resin does not differ systematically from that of the XAD-8 resin. The DAX-8 resin seems to have more precise column characteristics compared with the XAD-8 resin. There was no significant difference between the major elemental compositions of the parallel humic-solute bulks obtained by these two resins. According to the (13)C NMR spectroscopy the content and quality of aliphatic carbons, especially those representing terminal methyl groups or methylene carbons, were the most systematic and powerful discriminating factors between the humic extracts obtained by these two resins. Generally speaking the DAX-8 and XAD-8 resins seem to isolate humic-solute bulks almost equally, although the content of aliphatics is slightly greater for the former, producing mixtures with similar structural compositions for general purposes. The structural composition and quantity of the humic-solute mixture isolable with a weakly basic DEAE-cellulose anion exchange resin differs partially from any humic fraction obtained by non-ionic sorbing solids. The environmental impact was also visible on the quality of the structural fine-chemistry of the different humic isolates obtained both by the DAX-8 and XAD-8 resins. | 18,968,420 |
Determination of trace amounts of heavy metals in arctic ice core samples using inductively coupled plasma mass spectrometry. | Trace amounts of heavy metals in the ice cores from Canadian Arctic were analyzed using inductively coupled plasma mass spectrometry (ICP-MS). A custom made plastic device and ceramic knives were used to remove the contamination on the ice core surface. Ice cores could be broken into small sections (2-3 cm thick) after decontamination with the plastic device and ceramic knives. High-resolution depth profiles of various elements, i.e. As, Cd, Co, Cu, Ni, Pb, Zn and U, were thus attained. Concentrations in 518 ice core samples range from 0.1 (U) to 673.3 (Zn) pg g(-1). | 18,968,423 |
Application of solid-phase microextraction for the determination of organophosphorous pesticides in aqueous samples by gas chromatography with flame photometric detector. | A method based on solid-phase microextraction and gas chromatography flame photometric detector for the determination of organophosphorous pesticides (OPPs) in aqueous samples was described. Five kinds of commercially available fibers-7, 30 and 100 mum PDMS, 85 mum PA and 65 mum PDMS-DVB-were compared and 100 mum PDMS and 85 mum PA were the most sensitive fiber coatings for the analytes. The extraction time, extraction temperature, pH and content of NaCl were found to have significant influence on extraction efficiency. The optimized conditions were 100 mum PDMS fiber, 30 min extraction time at 40 degrees C, with 3% NaCl content and no pH adjustment. The linear range was 0.5-100 mug l(-1) for most of the analytes. The limits of detection (LODs) ranged from 0.049 mug l(-1) (for parathion) to 0.301 mug l(-1) (for carbophenothion) and RSD% of repeatability at the 10 mug l(-1) level were all below 8%. Environmental water samples were analyzed, but none of the analytes was detected. The recovery of spiked water samples was from 75.3 to 102.6%. | 18,968,428 |
Development of piezoelectric immunosensors for measurement of albuminuria. | The development of piezoelectric immunosensors for human serum albumin (HSA) is reported. The piezoelectric crystals were modified either with monoclonal antibody AL-01 (direct assay) or with HSA (competitive assay). Measurements were carried out in the flow-through mode. Affinity interaction between albumin and the antibody was characterised. With immobilised antibody and HSA in solution, the kinetic association rate constant k(a) was 18 100 l mol(-1) s(-1) and the dissociation constant k(d) was 0.00369 s(-1). For the opposite arrangement (immobilised HSA), a slower dissociation was observed, k(d) was 0.00085 s(-1). A competitive assay for HSA was developed with working range of 1-5 mug ml(-1) and a total time for one analysis equal to 17 min. Samples of urine were analysed after tenfold dilution. The developed system was successfully evaluated on real samples from diabetic patients and the obtained results correlated well with the standard reflectometric assay of proteins in urine. | 18,968,431 |
A multicommutation-based flow system for multi-element analysis in pharmaceutical preparations. | A flow system exploiting multicommutation and multidetection is proposed for sequential determinations in pharmaceutical preparations. The feasibilities were demonstrated by the determination of zinc, iron, copper, calcium and magnesium without changing the flow set-up. The gravitational flow of the solutions was exploited for addition of different chromogenic reagents and sample aliquots, thus avoiding the use of a propulsion unit. Transient signals at different wavelengths were measured simultaneously employing a fiber-optic multichannel spectrophotometer. Coefficients of variation of 1.0, 1.5, 1.4, 2.5 and 2.0% were obtained for iron, zinc, copper, calcium and magnesium, respectively. The mean sampling rate for the five species was 60 determinations per hour. In comparison to continuous reagent addition systems, the consumption was up to 160-fold lower. Results for pharmaceutical preparations agreed with those obtained by Flame atomic absorption spectrophotometry (FAAS) at the 95% confidence level. | 18,968,435 |
Recombinant single chain antibodies in bioelectrochemical sensors. | Recombinant antibodies provide an emerging strategy in the development of new immunosensors. In particular, single chain antibodies (scFvs) can be isolated and expressed in bacterial systems that also allow their in vitro manipulation at the gene level. In this work, we present for the first time results of single-chain phage displayed antibodies combined with amperometric detection and its application as an immunosensor. The scFv is immobilized on a carbon electrode and used to capture and quantify its specific target antigen. We describe the detection of the sugar milk lactose, the bacteria Listeria monocytogenes, and the enzyme MtKatG, which is expressed by Mycobacteriumtuberculosis. | 18,968,440 |
Multibiosensor based on enzyme inhibition analysis for determination of different toxic substances. | An original concept of an enzyme multibiosensor for determination of toxic substances based on enzyme inhibition analysis has been proposed and its main performances have been analysed. For the development of this multibiosensor, two types of transducers such as potentiometric pH-sensitive field-effect transistors and conductometric thin-films interdigitated electrodes, and three enzymes, namely urease, acetylcholinesterase and butyrylcholinesterase have been used. The experimental data have been treated by multivariate correspondence analysis. A complete procedure for a simultaneous determination of some heavy metal ions and pesticides has been proposed and its advantages have been discussed. | 18,968,442 |
Flow injection chemiluminescence determination of polyhydroxy phenols using luminol-ferricyanide/ferrocyanide system. | It was found that the weak chemiluminescence produced from the reaction of polyhydroxy phenols with luminol in alkaline solution could be strongly enhanced by ferricyanide and ferrocyanide. Based on this found, a new flow injection chemiluminescence method is proposed for the determination of four polyhydroxy phenols: pyrogallol, phlorglucinol, quinol and resorcinol. The detection limits of the method are 0.03 mug ml(-1) pyrogallol, 0.03 mug ml(-1) phlorglucinol, 0.04 mug ml(-1) quinol, and 0.02 mug ml(-1) resorcinol. The possible mechanism of CL reactions is also discussed briefly. | 18,968,456 |
Maleic acid-styrene encapsulated silica cation exchanger in high performance liquid chromatography. | The use of poly(maleic acid-styrene)-encapsulated silica for the determination of monovalent and divalent cations is well accepted in ion chromatography. The separation of Mn(2+), alkali and alkaline earth metal cations is obtained under the same chromatographic conditions. The influences of pH and the concentration of eluent on the retention of cations have been studied. The preparation conditions of packings were studied. The metal ions in the boiler water samples from a thermal power plant were quantitatively determined using this column. The results are in agreement with those determined by ICP and Volumetric analysis methods. | 18,968,461 |
Kinetics of europium(III) transport through a liquid membrane containing HEH(EHP) in kerosene. | Coupled transport of Eu(III) ions through a bulk liquid membrane containing mono(2-ethylhexyl)2-ethylhexyl phosphonate [HEH(EHP)] in kerosene has been examined. The influences of the carrier concentration, the HCl concentration in the stripping solution, the pH in the feed solution and the temperature were investigated. The transport of the Eu(III) ions is coupled by counter-transport of protons. The kinetics of the Eu(III) transport could be analyzed in the formalism of two consecutive irreversible first order reactions. The pseudo-first order apparent rate constants of the interfacial transport of the Eu(III) species are determined, varying temperature. The activation energy values are 14.0+/-1.0 and 54.0+/-3.4 kJmol(-1) for extraction and stripping, respectively. | 18,968,464 |
A high precision spectrophotometric method for on-line shipboard seawater pH measurements: the automated marine pH sensor (AMpS). | Measurement strategies for understanding the oceanic CO(2) (carbon dioxide) system are moving towards in situ and ship of opportunity sampling techniques. Automated instrumentation with high accuracy and sampling frequencies will enable a greater understanding of the fluxes of marine carbon and lead to a more reliable constrain on the calculated uptake of anthropogenic CO(2) by the oceans. This paper describes the automated marine pH sensor (AMpS); new instrumentation and methodology for the determination of seawater pH using dual spectrophotometric measurements of sulfonephthalein indicator in a semi-continuous seawater stream. The pH values measured during a recent study in the Weddell Sea are used to illustrate the excellent properties of the AMpS. The method has an on-line precision of better than 0.001 pH units and an estimated accuracy of better than 0.004 pH units. The instrument is compact, portable and has a measurement frequency of 20 samples per hour. The instrument is ideally suitable for operation on ships of opportunity. | 18,968,480 |
Fast determination of lead in lake sediment samples using electrothermal atomic absorption spectrometry with slurry samples introduction. | Lead concentration in lake sediment samples has been determined by means of ultrasonic slurry sampling electrothermal atomic absorption spectrometry USSS-ETAAS. The soil samples were suspended (0.025-0.15% w/v slurry) in four different liquid media containing 0.5% (v/v) nitric acid, 5% (v/v) nitric acid, 0.5% nitric acid+Triton X-100 and 5% nitric acid+Triton X-100. The effects of the instrumental operating conditions and slurry preparation on the signal were examined. Palladium and magnesium were used as modifiers to improve the signal quality. The procedure was validated by analysis of the certified reference lake sediment material LKSD-1, LKSD-2, LKSD-3 and LKSD-4. All analytical recoveries for lead in slurried lake sediment samples were satisfactory and varied from 95 to 104%. Relative standard deviation (R.S.D.) values were 4.8, 4.7, 4.5 and 5.5. The detection limits LODs of lead were 0.52, 0.45, 0.35, and 0.22 mug g(-1) for mass of sample 0.025, 0.050, 0.10 and 0.15 U, respectively. | 18,968,485 |
Identification and simultaneous determination of Azorubin, Allura red and Ponceau 4R by differential pulse polarography: application to soft drinks. | Azorubin (E 122), Ponceau 4R (E 124) and Allura red (E 129), are the most used red dyes in soft drinks manufacturing, and in some cases two dyes are present. The aim of this work is to show that using differential pulse polarography, it was possible to distinguish these synthetic dyes from the natural dyes providing from fruits. In addition, in an appropriate supporting electrolyte, identification and quantitative analysis of these three red dyes were possible, even when they were mixed. Various electrolytes were tested such as potassium chloride, which is a classical supporting electrolyte, citric acid which is one of the components of the soft beverages, sodium citrate and a phosphate buffer. It was shown that the peak intensities and potentials, and consequently their resolution, depend greatly on the pH values. In potassium chloride and sodium citrate the peaks of Azorubin, Allura red and Ponceau 4R were well separated and dyes were identified without ambiguity. Buffer solutions with pH close to 8 and 9 appeared to be appropriate, as the potentials and the intensities of the peaks were slightly changed when small amounts of soft drinks, usually at pH close to 3, were introduced in the cell. A procedure using the standard addition technique was developed, tested with model syrups and then applied to commercial syrups, soda and non-alcoholic bitters. | 18,968,486 |
Sample pretreatment on microfabricated devices. | The integration of sample pretreatment into microfluidic devices represents one of the remaining hurdles towards achieving true miniaturized total analysis systems (muTAS). The challenge is made more complex by the enormous variation in samples to be analyzed. Moreover, the pretreatment technique has to be compatible with the analysis device to which it is coupled in terms of time, reagent and power consumption, as well as sample volume. This review provides a thorough overview of the developments in this field to date. | 18,968,499 |
A microfabricated amperometric moisture sensor. | We describe a microfabricated moisture sensor with interdigitated Au or Pt electrodes on a silicon substrate. The sensor active area is covered with a spin-coated, baked-on layer of Nafion(R) perfluorosulfonate ionomer of submicron thickness. The sensor responds to moisture with a 10-90% rise time of 50-100 ms and a 90-10% fall time of 20-30 ms, faster than any other presently available sensor. The logarithm of the sensor current is related to the cube root of the moisture level at a given temperature. At 23 degrees C, the sensor easily measures relative humidities as low as 10%. The sensor response at a given absolute humidity level decreases exponentially with increasing temperature. The film is stable up to a temperature of 150 degrees C, permitting elevated temperature moisture measurement. Since sorbed water is actively decomposed electrolytically, the sensors exhibit negligible hysteresis. Response reproducibility of an individual sensor is <1%, that between identically made sensors is <5%, suggesting mass production techniques without individual calibration will be acceptable for all but the most demanding situation. | 18,968,503 |
A biosensor for monitoring formaldehyde using a new lipophilic tetrathiafulvalene-tetracyanoquinodimethane salt and a polyurethane membrane. | A format for a disposable screen-printed biosensor was investigated for monitoring formaldehyde. The screen-printed sensor format comprised a working electrode (WE) modified with platinised carbon, a new lipophilic tetrathiafulvalene-tetracyanoquinodimethane (TTF-TCNQ) salt as mediator, a plasticised polyurethane membrane (TECOFLEX SG80, PU) with anionic sites and the enzyme (formaldehyde dehydrogenase FOH) and co-factor (beta-NAD(+)). The new lipophilic TTF-TCNQ salt gave a smooth, robust electrode surface rather than microcrystalline deposits of the salt observed with TTF-TCNQ salts. Entrapment of the enzyme and co-factor behind a plastcised PU membrane with anionic sites enhanced the sensitivity and stability of the sensor. A linear response between 10(-3) and 10(-4) mol dm(-3) was observed. To demonstrate the feasibility of the use of the screen-printed sensor to monitoring formaldehyde in ambient air, preliminary experiments were carried out in the vicinity of a local medium density fibreboard factory and its performance compared to that of a biosensor made from the same platinised carbon and enzyme system, but without the lipophilic TTF-TCNQ and membrane, using a commercial 'Rank' cell. Samples were collected using a Molspin 'Super-sniffer'. | 18,968,517 |
Chemiluminescence muTAS for the determination of atropine and pethidine. | A novel chemiluminescence micro-total analytical system (muTAS) is described for the determination of atropine and pethidine. Reagents were moved though the 200-mum wide channels of a glass chip using a negative pressure pumping system. Linear calibrations were obtained for the system over three-orders of magnitude, with detection limits of 3.8x10(-9) and 7.7x10(-8) M, respectively for atropine and pethidine and R.S.D. of <5%. This is the first report on the use of muTAS to determine atropine with chemically oxidised tris (2,2'-bipyridine)ruthenium(II) chemiluminescence. | 18,968,526 |
Ruthenium(II) tris(bipyridyl) ion as a luminescent probe for oxygen uptake on the catalyzed oxidation of HSO(3)(-). | The present work describes an alternative technique for monitoring the rate of oxygen consumption during the oxidation of HSO(3)(-) catalyzed by manganese and iron ions. The method is based on the spectrofluorimetric monitoring of the quenching effect of molecular oxygen on the emission of the photoexcited [Ru(bipy)(3)](2+) ion, added to the reaction mixtures. The effects of Fe(III), at very low concentrations, and of Mn(II) on the oxidation of HSO(3)(-) by dissolved oxygen, have been investigated. The metal ions in the trivalent oxidation state react with HSO(3)(-) to initiate a radical chain reaction in which HSO(3)(-) is oxidized to sulfate and the metal ion is reduced to the divalent state. The synergistic effect of Mn(II) and Fe(III) was clearly evaluated. Possible parallel reactions with the oxygen indicator, [Ru(bipy)(3)](2+), are considered. | 18,968,527 |
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