title stringlengths 0 1.13k | abstract stringlengths 1 15.7k | PMID int64 22 36.5M |
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Simultaneous determination of the acid and basic ionization constants of imidazole. | The acid and base ionization constants of imidazole (LH) have been determined simultaneously by potentiometry. Concentration constants were obtained at 10.0, 15.0, 25.0 and 40.0 degrees with I = 0.1M (KNO(3)), the values (and standard deviations) at 25.0 degrees being pK(a1)(LH(2)(+)) = 7.002 +/- 0.006 and pK(a2)(LH(2)(+)) = 12.588 +/- 0.004. The following values were obtained for the corresponding thermodynamic parameters: DeltaH(1) =38 and DeltaH(2) = 38 kJ mole ; DeltaS(1) = -8 and DeltaS(2)= -112 J.mole(-1).K(-1). | 18,964,228 |
Relationship between muscle volume and muscle torque of the hamstrings after anterior cruciate ligament reconstruction. | The muscle torque per unit volume of the hamstrings on the injured and uninjured sides in patients with ACL reconstruction were compared with participants with no history of knee injury to examine whether a similar mechanism leading to quadriceps weakness exists in the hamstrings of these patients. The study population consisted of 18 and 52 patients at <or=6 and 12 months after ACL reconstruction, respectively, and 35 healthy controls. The hamstring volume was measured on MRI. To identify the muscle torque per unit volume, the peak torque of knee flexion was divided by the hamstring volume. Most muscle torque per unit volume indexes were not significantly different between the patients at <or=6 months (injured side: 0.133+/-0.03 Nm/cm(3), 60 degrees /s; 0.107+/-0.03 Nm/cm(3), 180 degrees /s; uninjured side: 0.139+/-0.02 Nm/cm(3), 60 degrees /s; 0.107+/-0.02 Nm/cm(3), 180 degrees /s) and controls (0.170+/-0.05 Nm/cm(3), 60 degrees /s; 0.121+/-0.05 Nm/cm(3), 180 degrees /s). However, the muscle torque per unit volume of patients at 12 months in both injured (0.118+/-0.03 Nm/cm(3), 60 degrees /s; 0.092+/-0.02 Nm/cm(3), 180 degrees /s) and uninjured sides (0.120+/-0.03 Nm/cm(3) at 60 degrees /s; 0.094+/-0.02 Nm/cm(3), 180 degrees /s) were significantly lower than those of controls (P<0.01). We found no evidence of recruitment disorder in the hamstrings of the patients. The results of this study indicated that the mechanism of muscle weakness of the hamstrings after reconstruction was different from that of the quadriceps, although the precise mechanism remains to be determined. | 18,964,233 |
[Not Available]. | The three natural xanthines, caffeine, theobromine and theophylline, have been determined by HPLC on columns of silica gel or a C(18)-bonded phase. For the determination in beverages, HPLC on silica gel was used. The method was applied to coffee, tea, maté, in extracts or in the drinks themselves. For the extracts a comparison was made with other methods for determining caffeine, HPLC seems a method well suited to analysis of complex matrices for the xanthines. | 18,964,243 |
Analytical chemistry in the Soviet Union. | The history of the development of analytical chemistry in the Soviet Union is briefly outlined. Organizations co-ordinating research in this field, and the leading scientific centres, are indicated. Achievements in various analytical techniques are reviewed. Analytical services in some branches of the economy, and the analysis of most important materials are considered. Major publications are pointed out and international contacts of Soviet experts are discussed. | 18,964,256 |
Steric and hydrophobic effects of substituents in extraction of metal complexes with O,O-dialkyldithiophosphoric acids. | The two-phase stability constants (equilibrium constants) of metal complexes MA(n) [M(n)(+) = Ni(II), Zn(II), Cd(II), Pb(II), Tl(I), In(III)] with a series of O,O-dialkyldithiophosphoric acids in the system water-organic solvent) have been determined. By use of correlation analysis the role of the steric and hydrophobic effects of the substituents at the phosphorus atom on the stability constant beta(n) and distribution constant P of the complexes has been elucidated. The data obtained are of use for determining the relationships in the influence of structure of a reagent on its extraction properties and on the conditions for practical application of O,O-dialkyldithiophosphoric acids for metal extraction. | 18,964,282 |
Extraction and preconcentration of selenium from aqueous solutions and its determination in water and hair samples by atomic-absorption spectrophotometry. | Several organic solvents, including benzene, xylene, toluene, nitrobenzene, chloroform, carbon tetrachloride, chlorobenzene and high molecular-weight pyridines such as 4-(5-nonyl)pyridine, 2-hexyl-pyridine and benzylpyridine have been investigated as components of systems for the extraction and preconcentration of selenium from nitric acid solutions containing iodide. The results are discussed in terms of choice of reagents and the acid and iodide concentrations, and of several other parameters affecting the extraction. The utility of the method for separation of selenium from aqueous solution has been evaluated. The method has been used for preconcentration of trace levels of selenium from water and hair samples for determination by atomic-absorption spectrophotometry. | 18,964,309 |
[Not Available]. | This paper describes the theoretical basis of a new program for refinement of complex stability constants together with the other parameters of various protometric titrations. The method is based on minimization of the sum of the weighted squares of the residuals of the experimental variables reagent volume and E or pH. A new exploitation of mathematical relations allows simultaneous refinement of the various parameters and unknown free ion concentrations. After convergence, the program PROTAF also provides the adjusted values of experimental variables. | 18,964,321 |
Behaviour of a chalcocite copper ion-selective electrode in solutions of iron(III) ions. | The effect of iron(III) ions on the potential of the chalcocite electrode was investigated. Linear graphs were obtained for pFe(III) = 2-4, and were suitable for analytical purposes. The effect of ligands complexing iron(III) was studied, and the potential shown to be due to the concentration of free iron(III) ions only. The pH effect is mainly connected with solution reactions. A mechanism of potential response, based on a redox reaction, has been postulated, but the response does not depend on the redox potential in the bulk of the solution. | 18,964,324 |
Constant Calcein Blue: An indicator for spectrofluorometric calcium determination. | A new fluorescent indicator for metal ions, called Constant Calcein Blue, has been synthesized by condensing 7-hydroxy-2,3-dimethylchromone, iminodiacetic acid and formaldehyde. The indicator exhibits extraordinary resistance to alkaline hydrolysis and is recommended for spectrofluorometric determinations of metal ions, such as calcium, that must be performed at pH 10.5 and higher. | 18,964,328 |
A sub-microlitre two-photon ionizatio detector for high-performance liquid chromatography. | A simple sub-microlitre two-photon ionization detector for high-performance liquid chromatography has been constructed; it basically consists of a pulsed laser, a falling-jet cell, and a boxcar detection system. The performance of the cell has been evaluated; the cell is windowless and its volume is about 14 nl. A dye laser is applicable as excitation light-source. | 18,964,337 |
Phthalhydrazidylazoacetylacetone as a chemiluminescent acid-base indicator. | Phthalhydrazidylazoacetylacetone, an azo derivative of luminol, has been shown to be superior to luminol as a chemiluminescent indicator for acid-base titrations. | 18,964,346 |
Polargraphic adsorptive waves of alkaline-earth metal complexes with thymolphthalexone. | Sensitive derivative polarographic adsorption waves have been observed for alkaline-earth metal-TP complexes in 0.15M potassium hydroxide containing 3 x 10(-5)M thymolphthalexone (TP). The limit of detection for calcium, strontium and barium was 7.5 x 10(-7)M and for magnesium 4.0 x 10(-6)M. The proposed method has been used successfully for determining trace amounts of calcium in natural waters and hair samples. The composition of the complex has been shown to be 1:1 alkaline-earth metal:TP and various experiments have confirmed that the wave is an adsorption wave. The reaction mechanism has been studied by a number of methods. | 18,964,358 |
Anodic-stripping voltammetric determination of arsenic at a copper-coated glassy-carbon electrode. | The anodic-stripping voltammetric behaviour of arsenic(III) at a glassy-carbon electrode copper-coated in situ has been investigated. The effects of copper concentration, acidity, deposition potential and sweep rate on the stripping peak have been examined and criteria are given for the choice of experimental conditions. The procedure is applicable to the determination of 7.5-750 ng/ml of arsenic levels and is useful for the analysis of various types of water sample. | 18,964,362 |
Signal processing with a summing operational amplifier in multicomponent potentiometric titrations. | It has been proved that application of two indicator electrodes connected to the ordinary titration apparatus through an auxiliary electronic device (a summing operational amplifier) significantly extends the scope of multicomponent potentiometric titrations in which the analytes are determined simultaneously from a single titration curve. For each analyte there is a corresponding potential jump on the titration curve. By application of the proposed auxiliary device, the sum of the electrode potentials is measured. The device also enables the relative sizes of the potential jumps at the end-points on the titration curve to be varied. The advantages of the proposed signal processing are exemplified by complexometric potentiometric titrations of Fe(III) and Cu(II) in mixtures, with a platinum electrode and a copper ion-selective electrode as the indicator electrodes. | 18,964,366 |
[Not Available]. | The isotherms for adsorption of some organic molecules on asbestos fibres have been determined by gas chromatography. The results show that the adsorption mechanism lies somewhere between physisorption and chemisorption. The degree of adsorption at a given temperature, for the compounds studied, is toluene > tetrahydrofuran > benzene > dichloromethane. | 18,964,367 |
Spectrophotometric determination of iron by extraction of the iron(II)-5,5-dimethyl-1,2, 3-cyclohexanetrione-1,2-dioxime-3-thiosemicarbazone complex. | The iron (II)-5,5-dimethyl-1,2,3-cyclohexanetrione-1,2-dioxime-3-thiosemicarbazone complex can be extracted from a medium of high acidity into amyl alcohol. Measurement of the absorbance at 550 nm gives a determination limit for iron of 0.015 mu/ml. The method has been applied to the determination of iron in water, wine, beer and fruit juice. | 18,964,380 |
Hydrodynamic voltammetry at tubular electrodes-III Determination of traces of bismuth by differential-pulse anodic-stripping voltammetry at a glassy-carbon tubular electrode with in situ mercury plating. | An equation for the current in differential-pulse anodic-stripping voltammetry at tubular electrodes is derived. Application of a glassy-carbon tubular electrode to determination of traces of bismuth in environmental water samples by differential-pulse anodic-stripping voltammetry is described. In hydrochloric acid medium, the stripping peak current is proportional to the concentration of bismuth in the range 2-100 ng/ml, with a deposition time of 3-10 min. The detection limit is 0.5 ng/ml. | 18,964,381 |
Determination of hydrogen peroxide with N,N-diethylaniline and 4-aminoantipyrine by use of an anion-exchange resin modified with manganese-tetrakis(sulphophenyl)porphine, as a substitute for peroxidase. | Amberlite IRA 900 anion-exchange resin modified with manganese-tetrakis(sulphophenyl)-porphine has been used as a catalyst instead of peroxidase for the determination of hydrogen peroxide by the reaction 2H(2)O(2) + N,N-diethylaniline + 4-aminoantipyrine (catalyst)--> quinonoid dye (lambda(max) 550 nm) + 4H(2)O. The apparent molar absorptivity for hydrogen peroxide was 1.1 x 10(4) 1.mole(-1).cm(-1), coefficient of variation 0.7%. This value is approximately 84% of that obtained by the use of peroxidase as catalyst. Similar conditions to those in the enzymatic reaction were suitable for use of the modified resin as catalyst, and the results show it to be a good substitute for peroxidase in this reaction system. | 18,964,384 |
Determination of alkaline-earth metals in foetus bones by inductively-coupled plasma atomic-emission spectrometry. | Alkaline-earth metals in human bone samples have been determined simultaneously by inductively-coupled plasma atomic-emission spectrometry (ICP-AES). Results obtained by atomic-absorption spectrometry for Mg, Sr and Ba, and complexometry for Ca, have been compared with those by ICP-AES for a laboratory-control bone sample. Accuracy and precision were examined by analysing the IAEA animal bone standard (H-5). Agreement with the certified values to within 5% was obtained. The concentrations of the elements in foetal bone have also been determined. | 18,964,414 |
A simple and rapid fluorimetric method for the microdetermination of isonicotinic acid hydrazide. | A simple, rapid and sensitive fluorimetric method has been developed for the microdetermination of isonicotinic acid hydrazide, based on its formation of a hydrazone with 2-hydroxy-1-naphthaldehyde in acidic medium, in the presence of excess of scandium ions, and the consequent formation of a strongly fluorescent complex (lambda(ex) 430 nm, lambda(em) 510 nm) between the hydrazone and scandium in weakly acidic medium. Kinetic and equilibrium procedures for isonicotinic acid hydrazide determination are proposed. A calibration graph linear up to 5.00 mug/ml is obtained by both procedures, with a mean relative error of about 2.0%. The detection limit for the kinetic procedure is 0.4 ng/ml and for the equilibrium procedure about 0.2 ng/ml. | 18,964,419 |
Hydroxide complexes of lanthanides-VIII Lanthanum(III) in perchlorate medium. | From the precipitation borderline in the pLa'-pC(H) diagram the stability constants for (mononuclear) lanthanum-hydroxide species have been established. The presence of polynuclear species could not be demonstrated and seems unlikely. The values found were log *beta(1) = -8.6, log *beta(2) = -17.9, log *nu(3) = -27.3 and log *K(s0) = 22.8. The data refer to precipitates prepared under CO(2)-free conditions at room temperature (21.5 +/- 0.5 degrees ) in sodium perchlorate medium with an ionic strength of 1. | 18,964,420 |
Some analytical aspects of the measurement of heavy-atom kinetic isotope effects. | Measurements of the kinetic isotope effects of heavy atoms are discussed from an analytical point of view. The discussion includes the choice of isotope, the procedure for measurement, and methods for increasing the kinetic isotope effect. The procedures most commonly used and newly developed techniques are presented and their advantages and disadvantages considered. | 18,964,423 |
Determination of viscosity with an open-closed flow-injection system. | A flow-injection configuration for the determination of the viscosity of water-miscible samples is proposed. The method is based on the use of an open-closed flow-injection system involving a trapped sample (carrier) and injection of a dye plug. The behaviour of the plug is monitored photometrically by a detector included in the circuit. The parameters of the multipeak recording obtained are related to the viscosity, which can be determined in the range 1-28 cp with an r.s.d. of about +/- 1 %. | 18,964,432 |
Extraction of aromatic organic compounds by polyurethane foam. | The mechanism of extraction of organic compounds by open-cell polyurethane foam has been investigated through a detailed study with simple aromatic compounds. Comparison with identical extractions into diethyl ether suggests that the basic extraction mechanism is an ether-like solvent extraction process. The addition of salt increases the extraction and changing the dielectric constant of the aqueous solution also affects the extraction. For organic compounds which have a group capable of hydrogen bonding, some additional factor appears to influence the extraction. This appears to be hydrogen bonding with the polyurethane foam; it is stronger with polyether foam and reduced by the presence of a strong intramolecular hydrogen-bonding group placed ortho to the hydrogen-bonding group. Thermodynamic studies support these conclusions. | 18,964,439 |
A rapid spectrophotometric method for determination of piperazine. | A spectrophotometric method has been developed for the determination of piperazine and its salts (citrate, phosphate, and tartrate) without prior separation, based on the interaction of piperazine or any of its salts with phenothiazine and N-bromosuccinimide in aqueous methanol. The products exhibit absorption maxima at 448, 595 and 645 nm. Measurements are made at 595 nm. Beer's law is obeyed in the concentration range 0.5-5 mug/ml for piperazine salts and 0.5-3 mug/ml for piperazine hexahydrate. The method is rapid, simple and successful for analysis of some pharmaceutical preparations. | 18,964,442 |
Determination of arsenic in ores, concentrates and related materials by graphite-furnace atomic-absorption spectrometry after separation by xanthate extraction. | A method for determining approximately 0.2 mug/g or more of arsenic in ores, concentrates and related materials is described. After sample decomposition arsenic(V) is reduced to arsenic(III) with titanium(III) and separated from iron, lead, zinc, copper, uranium, tin, antimony, bismuth and other elements by cyclohexane extraction of its xanthate complex from approximately 8-10M hydrochloric acid. After washing with 10M hydrochloric acid-2% thiourea solution to remove residual iron and co-extracted copper, followed by water to remove chloride, arsenic is stripped from the extract with 16M nitric acid and ultimately determined in a 2% nitric acid medium by graphite-furnace atomic-absorption spectrometry, at 193.7 nm, in the presence of thiourea (which eliminates interference from sulphate) and palladium as matrix modifiers. Small amounts of gold, platinum and palladium, which are partly co-extracted as xanthates under the proposed conditions, do not interfere. | 18,964,463 |
Simultaneous determination of low concentrations of ammonium and potassium ions by capillary type isotachophoresis. | Low concentrations of ammonium and potassium ions (<2.0 mg/l.) were determined simultaneously by capillary type isotachophoresis based on the interaction between potassium and 18-crown-6 in the aqueous leading electrolyte. The PU value of potassium ion increased with increasing concentration of 18-crown-6 up to 3mM, whereas that of the ammonium ion remained almost constant. Thus complete separation of ammonium and potassium ions could be obtained by using 1-3mM 18-crown-6. The error in the analysis of mixtures containing ammonium and potassium ions (250-mul sample injection) was less than +/- 20% with a leading electrolyte containing 3mM 18-crown-6. The analysis time was 18 min. | 18,964,464 |
A fiber-optic sensor for CO(2) measurement. | A fiber-optic sensor has been prepared which responds to carbon dioxide at physiologically significant concentrations. It is based on pH modulation by dissolved carbon dioxide in a sensing layer of fluorescent dye. By use of a previously developed methodology by which the sensing chemistry is bonded directly to the glass fiber tip, the miniature size of the sensor is preserved. This method involves consecutive applications of solution polymers to the fiber tip rather than mechanical attachment of sensor reagents. Preparations of polymer-immobilized dyes and polymer membranes are described. | 18,964,477 |
Solid-state instrumentation for use with optical-fibre chemical-sensors. | A solid-state instrument has been developed for use with optical-fibre pH-sensors, which incorporates light-emitting diode sources and a photodiode detector. The instrument has an internal reference. The optical and electronic principles are described. The responses of the sensor and instrument are reported and compared with those obtained with conventional instrumentation. | 18,964,485 |
Determination of uranium at trace levels by radiochemical neutron-activation analysis employing radioisotopic yield evaluation. | Nanogram and picogram quantities of uranium were determined in biological materials by radiochemical neutron-activation analysis. Two different approaches using either (239)U or (239)Np were employed for cross-checking, and the question of negative errors due to incomplete acid dissolution of any possible inorganic (siliceous) fraction was studied. In the first and main approach, radiochemical separation of the short-lived (239)U (23.5 min) nuclide was based on TBP extraction following rapid conventional wet-ashing. Addition of large amounts of uranium carrier (ca. 50 mg) allowed the chemical yield to be evaluated from the gamma spectrum of the isolated fraction by means of the 186 keV peak of (235)U. In the second approach, the longer-lived (239)Np (56.5 hr) daughter was separated by anion-exchange; this nuclide allowed use of lengthier dissolution procedures employing total decomposition with hydrofluoric acid. Nanogram quantities of (237)Np were irradiated simultaneously with the sample and an aliquot of the resulting solution containing (237)Np and (238)Np (51 hr) was added prior to sample destruction, these isotopes serving as carrier and yield tracer, respectively. Results are presented for a series of reference materials. The methodologies and results from the two approaches are discussed and evaluated. | 18,964,488 |
Modified reverse pulse polarographic behaviour of magnesium ion in aqueous solution. | Modified reverse pulse polarography (MRPP) is proposed for measuring the quantity of a reduction product formed at the initial potential in reverse pulse polarography. A double potential-step method is employed for this purpose. MRPP has been applied to the study of the electrochemical behaviour of magnesium in aqueous solution. For magnesium the height of the MRPP anodic wave was proportional to concentration at low pH, but not in unbuffered neutral solution. This difference is attributed to formation of hydroxo-magnesium complexes because of depletion of hydrogen ions near the electrode in a neutral solution. | 18,964,504 |
Determination of the sum of rare-earth elements by flow-injection analysis with Arsenazo III, 4-(2-pyridylazo)resorcinol, Chrome Azurol S and 5-bromo-2-(2-pyridylazo)-5-diethylaminophenol spectrophotometric reagents. | The reactivity of Arsenazo III, Chrome Azurol S in the presence of cetyltrimethylammonium or cetylpyridinium bromide, 4-(2-pyridylazo)resorcinol and 5-bromo-2-(2-pyridylazo)-5-diethylaminophenol with various rare-earth elements (REE) has been studied and the optimum conditions have been established for the spectrophotometric determination of REE with stationary and flow systems. Arsenazo III is the most suitable for the determination of the sum of REE, especially La, Ce, Nd, by FIA with spectrophotometric detection at 660 nm, in systems containing 0.04 mM reagent and 0.2M formate buffer (pH 3) and for sample volumes of 30 mul. The detection limits are 10.8 ng La, 11.0 ng Ce and 9.4 ng Nd in 30 mul. Limited amounts of Fe(III) and Al(III) are screened with 10 mM ascorbic and 5-sulphosalicylic acids. The sum of the REE is obtained from calibration plots prepared with La(III) standard solutions. The method has been successfully used for apatites and REE oxide concentrates after various kinds of decomposition. | 18,964,509 |
Determination of borate ion-pair stability constants by potentiometry and non-approximative linearization of titration data. | Borate anions, B(OH)(-)(4), are known to associate with alkali and alkaline-earth metal cations in sea-water. The borate cation ion-pairs are of the general form MB(OH)((n-1)+)(4), where M(n+) is the cation. In this work, the cation borate stability constants (K*(MB)) have been evaluated for Na(+), Li(+), Mg(2+), Ca(2+) and Sr(2+) where K*(MB) = [MB(OH(4))((n-1)+)]/[M(n+)][B(OH)(-)(4)]. The K*(MB) values were obtained from values found for the stability constant of boric acid (K*(B)) in various electrolyte media at 25 degrees and an ionic strength of 0.7. Acid-base potentiometric titrations were performed in the electrolyte media with a standard Pt/H(2) electrode and a junctionless Ag/AgCl reference electrode to monitor the emf. A non-approximative equation was used to linearize the titration data. The values obtained were: K*(Lib) = 0.89 +/- 0.02, K*(NaB) = 0.44 +/- 0.01, K*(MgB) = 13.6 +/- 0.7, K*(CaB) = 11.4 +/- 0.15, K*(SrB) = 3.47 +/- 0.06. The values for K*(MB) correlate with the charge-density parameter z(2)/(r + 0.85), where r is the radius of the cation. The speciation of boron in sea-water was predicted from the K*(MB), data for the major cations present. | 18,964,511 |
The influence of atomization pressure on the behaviour of aluminium in electrothermal atomic-absorption spectrometry. | Pressurized atomization in argon purge gas considerably enhances the peak area in AAS determination of aluminium, owing to the decrease in the diffusion rate of atoms with increasing pressure. If lower heating rates are used, the diffusional loss mechanism becomes more important. Thus pressure then has an even more pronounced influence on signal strength. Atomization under pressure in argon purge gas is shown to be beneficial only for light elements. It can be expected that if instrumental matrix modification is made by using hydrogen as purge gas, increasing the atomization pressure may prove beneficial for all elements. | 18,964,541 |
HPLC separation of heterocyclic beta-diketonates of actinide, lanthanide and transition metals. | Liquid-chromatography conditions for the separation of neutral chelates of 1-phenyl-3-methyl-4-benzoyl-5-pyrazolone with transition metals, lanthanides and actinides have been established. The use of reverse-phase liquid chromatography, instead of ion-exchange, is a novel approach for actinide separation. The high molar absorptivities of the beta-diketonates in the ultraviolet region allow for their detection at the nanogram level. The potential exists, therefore, for the rapid solvent extraction, concentration and determination of traces of actinides and other metals. | 18,964,552 |
Determination of two metals from a single potentiometric titration curve The application of two indicator electrodes. | The advantages of applying two indicator electrodes in complexometric potentiometric multicomponent titration are shown by means of simulated titration curves. Two measurement arrangements have been considered, one in which the indicator electrodes are directly connected to a voltmeter and the other in which the electrodes are connected to the voltmeter through a summing operational amplifier. They have been compared with the conventional arrangement of a single indicator electrode and a reference electrode. The influence of the stability constants of the complexes in solution and of the electrode parameters on the shape of titration curves has been examined. It is shown that the use of two indicator electrodes may significantly increase the applicability of multicomponent potentiometric titrations. | 18,964,554 |
Analysis of mixtures of purines and pyrimidines by first- and second-derivative ultraviolet spectrometry. | Zero-order, first-derivative and second-derivative ultraviolet absorption spectra of a series of purines, pyrimidines and their binary mixtures in aqueous solution have been recorded at 298 K. It is shown that second-derivative spectra can be used for the identification of eight mixtures of purines and pyrimidines. Several graphical procedures are tested for evaluating derivative spectra in quantitative measurements of single compounds and mixtures. Linear log-log calibration plots are obtained with correlation coefficients generally larger than 0.99. Second-derivative spectra appear to provide a precise and simple method for determination of purines and pyrimidines, at concentrations ranging between 5 x 10(-6) and 5 x 10(-4)M. | 18,964,565 |
A PVC-coated carbon rod ion-selective electrode for thallium and its application to the analysis of rocks and minerals. | A new Tl(III) ion-selective electrode prepared by coating a graphite rod with a PVC membrane has been made and investigated. The optimum membrane composition is Butylrhodamine B-TlCl(-)(4) 5 mg, chlorobenzene 0.1 ml, dioctyl phthalate 0.4 ml, PVC 0.17 g. The electrode exhibits Nernstian response to Tl(III) over the concentration range 6.5 x 10(-7)-2.5 x 10(-3)M. The detection limit is 3.5 x 10(-7)M and the slope of the electrode response is 53 +/- 1 mV per decade. The electrode shows high stability and selectivity. The electrode is easy to make and store, and inexpensive. | 18,964,574 |
Separation of selenium(IV) and tellurium(IV) from mixtures by extraction chromatography with trioctylphosphine oxide. | The reversed-phase extraction chromatographic separation of selenium(IV) and tellurium(IV) from several elements with trioctylphosphine oxide as extractant is reported. Selenium was extracted from 6M hydrochloric acid containing 7M lithium chloride was stripped with 4M hydrochloric acid, and tellurium was extracted from either the same medium as selenium or from 4M hydrochloric acid, and stripped with 1-2M hydrochloric acid. Selenium and tellurium can be separated from multicomponent mixtures. | 18,964,576 |
A rapid algorithm for solution of the equations of multiple equilibrium systems-RAMESES. | The solution of systems of equilibrium is an important though commonplace operation, rendered difficult by non-linearity. Previous methods of numerical solution have suffered from slow convergence, unreliability, and inefficient structure. An algorithm, RAMESES, is presented in matrix algebra terms, which is both simple in structure and efficient, involving only one matrix inversion per system and giving an exact solution of the set of dependent equilibrium equations at each iteration. | 18,964,599 |
Metal complexes of 1-oxa-4,7,10-triazacyclododecane-N,N',N''-triacetic acid. | The macrocyclic complexone 1-oxa-4,7,10-triazacyclododecane-N,N',N''-triacetic acid (cODTA) has been synthesized and its protona constants, stability constants of metal complexes and enthalpy changes for the formation of alkaline-earth complexes have been determined. Although it is not so powerful a complexing agent as the N-acetate derivative of the corresponding tetra-aza macrocycle, cDOTA, this is still one of the strongest complexones known, particularly towards the alkaline-earth metals. The complexes of the transition metals are also very stable and there is an inversion of the Irving-Williams order of stability for the complexes of cobalt and nickel. | 18,964,608 |
Derivative ultraviolet-visible region absorption spectrophotometry and its analytical applications. | Theoretical aspects, instrumental devices and analytical applications of derivative ultraviolet-visible region absorption spectrophotometry are reviewed. | 18,964,610 |
Examination of guanosine and xanthosine nucleotides by HPLC and electrochemical detection. | The suitability of electrochemical detection (ECD) following HPLC separation of guanosine, xanthosine and adenosine nucleotides has been evaluated. Separation of five monophosphates of guanosine was achieved by using a reversed-phase column; di- and triphosphates have also been separated from monophosphates. Adenosine compounds are insensitive to ECD. | 18,964,643 |
Catalytic-adsorptive stripping voltammetric measurements of hydrazines. | Hydrazine compounds can be determined by voltammetry, based on their hydrogen catalytic wave in formaldehyde-platinum-sulphuric acid media. Adsorption of the platinum-formazone complex on the hanging mercury drop electrode enhances the sensitivity, allowing convenient measurement of micromolar and submillimolar concentrations of simple hydrazines. The selectivity is better than that of conventional (anodic) measurements of hydrazines, as oxidizable compounds do not interfere. The sensitivity is also greatly improved. The hydrazine response is evaluated with respect to preconcentration time, concentration dependence, platinum and formaldehyde concentrations, reproducibility and other variables. The relative standard deviation (at 2 x 10(-5)M) is 1.6%. | 18,964,656 |
A new method for the iodometric determination of sulphoxides. | A method is described for determination of sulphoxides through their reaction with iodide in a trifluoroacetic acid/acetone medium to produce iodine, which is then titrated with thiosulphate. | 18,964,657 |
Solid state chemical ionization for characterization of organic compounds by laser mass spectrometry. | A new technique involving the addition of a compound to the analyte to serve as a source of "reagent" ions has been developed for negative-ion laser mass spectrometry. This "solid state chemical ionization" leads to ions characteristic of the analyte, owing to ion-molecule reactions between the "reagent" ion and the neutral analyte in the laser-generated plume. Polycyclic aromatic hydrocarbons show formation of an ion corresponding to (M + O - H)(-) in their negative-ion laser mass spectra when mixed with compounds such as sym-trinitrobenzene, sodium nitrate and sodium peroxide. NO(-)(2), O(-), and O(-)(2) serve as "reagent" ions in these compounds. Formation of (M + Cl)(-) is seen in the laser mass spectra of glycosides mixed with hexachlorobenzene. Chloride serves as the "reagent" ion in this case. | 18,964,680 |
Strategies for the reversible immobilization of enzymes by use of biotin-bound anti-enzyme antibodies. | Glucose oxidase (E.C. 1.1.3.4) is reversibly immobilized in a reactor coupled to a flow-injection analysis system using an immunological reaction. The antibody used is irreversibly immobilized on the reactor support by an avidin-biotin linkage. The bond between avidin and biotin is nearly irreversible under normal elution conditions for antibody-antigen reactions. The reactor is packed with a support on which avidin is covalently attached and a biotin-bound second antibody is passed over the reactor packing, which immobilizes this antibody. An immune complex of the enzyme, or first anti-enzyme antibody followed separately by enzyme, is introduced into the flow system, resulting in enzyme immobilization. The reactor produced can be used in the determination of 1 x 10(-11) -1 x 10(-6) mole of glucose with a sample size of 20 mul and a sample throughput of 20-30/hr. These results are comparable to or better than those obtained with glucose oxidase directly immobilized on the same support. The enzyme can be removed by elution with low-pH buffers, and the reactor regenerated by injection of the anti-enzyme antibody and the enzyme. | 18,964,697 |
Temperature effects on the solid-matrix luminescence properties of 4-phenylphenol adsorbed on filter paper. | Experimental values of fluorescence quantum yield, phosphorescence quantum yield, and phosphorescence lifetime were obtained at temperatures from 23 degrees to -180 degrees for 4-phenylphenol adsorbed on filter paper. From the experimental values, rate constants for phosphorescence and radiationless transition from the triplet state were calculated along with the triplet formation efficiency. The data revealed several important aspects that are responsible for the room-temperature fluorescence and phosphorescence of 4-phenylphenol adsorbed on filter paper. | 18,964,707 |
Determination of zirconium in steels. | The determination of zirconium in the range 0.01-0.20% is required for some special alloy steels. A method has been developed, based on initial removal of iron as its chloro-complex by extraction with methyl isobutyl ketone, followed by further extraction after addition of potassium thiocyanate, and determination of the zirconium left in the aqueous phase, with Arsenazo III. The absorbance is measured at 665 nm. | 18,964,725 |
Selective ion-exchanger behaviour of neutral carrier ion-selective electrode membranes. | Radiotracer experiments confirm that neutral carrier ion-selective electrodes made from plasticized PVC are low-capacity selective ion-exchangers. The ion-exchange selectivity is closely correlated to potentiometric selectivity. | 18,964,726 |
Mixed reagents in multicomponent flow-injection analysis Simultaneous determination of iron and copper in blood serum with mixed bathocuproinedisulphonate and bathophenanthrolinedisulphonate or ferrozine. | Mixtures of 0.6mM bathocuproinedisulphonate (BC) and 0.2mM bathophenanthrolinedisulphonate (BP) or 2mM BC and 0.2mM ferrozine (FZ) were used for a rapid determination of iron and copper in deproteinated blood serum in the presence of 0.1M formate buffer (pH 3.5), 10mM ascorbic acid and 0.3M trichloroacetic acid, by two variants of multicomponent FIA with a diode-array detector (MC-FIA). Merging zones MC-FIA is especially suitable for the determination of 0.7-33muM Fe and 0.4-35muMCu, for Cu:Fe concentration ratios from 10:1 to 1:10and with RSD <3 or 2% for Fe or RSD <6 or 5% for Cu in artificial mixtures and deproteinated standard blood sera, respectively, and relative errors of less than 3-5%. The concentrations of both elements were calculated according to a simple computer program (ORTHO) for overdetermined systems (10 or 11 wavelengths), but evaluation at the absorption maxima for the individual chelates (at 2 or 3 wavelengths) also gave satisfactory results. | 18,964,739 |
Determination of acriflavine, rivanol, Acridine Orange, Acridine Yellow and proflavine by a catalytic photokinetic method. | A fast and sensitive photokinetic method for the determination of acriflavine, rivanol, Acridine Orange, Acridine Yellow and proflavine is described. It is based on the rate of photoreduction of methylviologen in the presence of EDTA, sensitized by these diaminoacridines. The rate is monitored spectrophotometrically by the formation of ferroin, which is generated after reduction of iron(III) by the methylviologen cation radical in the presence of 1,10-phenanthroline. The method has been successfully applied to the determination of acriflavine and rivanol in pharmaceuticals. | 18,964,758 |
Estimation of kinetic parameters from thermochemical data. | A method is described by which kinetic parameters may be calculated from the measured temperature changes caused by the heat produced during a chemical reaction. An isoperibol titration calorimeter with an ampoule-breaking facility is used to obtain the temperature data. The temperature changes resulting from the reaction between tri-isopropyl phosphite and sulphur (S(8)) are used as an example to demonstrate the effectiveness of the method. The temperature changes are used to calculate an enthalpy of reaction. From the enthalpy of reaction and intermediate heats, instantaneous concentrations of the reactants may be calculated. | 18,964,761 |
Ion flotation behaviour of thirty-one metal ions in mixed hydrochloric/nitric acid solutions. | The ion flotation of 31 metal ions in hydrochloric/nitric acid solution with the cationic surfactant cetylpyridinium chloride was investigated. A 25-ml portion of 0.27-2.87 x 10(-4)M metal ion and 1.8-6.0 x 10(-4)M cetylpyridinium chloride solution in 0.17-3.4M acid mixture ([HCl]:[HNO(3)] = 2.4:1) was subjected to flotation in a cell, 22.5 cm high and 4.0 cm in diameter, for 5 min, with nitrogen bubbles. Ir(IV), Pt(IV), Ge(IV), Sn(IV), Bi(III), Au(III), Tl(III), Pd(II) and Sn(II) were floated from solution in 95-100% yield; Ru(III), Rh(III), Ir(III), Hg(II), Ag(I) and Tl(I) were partly floated, while Cr(VI), Ti(IV), Zr(IV), Ga(III), In(III), Fe(III), Sb(III), Al(III), Mn(II), Fe(II), Co(II), Ni(II), Cu(II), Zn(II), CD(II) and Pb(II) were floated with less than 20% yield. The flotation behaviour of these metal ions in the mixed acid system was compared with that in hydrochloric acid. The flotation is more efficient in the mixed acid system. | 18,964,771 |
Second derivative spectrophotometric determination of iron by extraction of the ferroin-perchlorate ion-association complex into mesityl oxide. | A highly selective and sensitive second-derivative spectrophotometric determination of iron is based on the extraction of the ferroin-perchlorate ion-association complex into mesityl oxide. A linear calibration graph is obtained for iron in the range 0.5-50 mug in 100 ml of original aqueous phase, with a detection limit of 2 ng/ml. The method is precise and reliable and has been applied to the determination of iron in high-purity rare-earth oxides. | 18,964,786 |
Reactivity of the cadmium ion in concentrated phosphoric acid solutions. | The solvation transfer coefficients which characterize the changes of ion reactivity with phosphoric acid concentration have been calculated for cadmium from the constants of the successive chloride complexes, and for silver and diethyldithiophosphate from potentiometric measurements. They evidence the strong desolvation of the cadmium species in concentrated phosphoric acid media, causing a remarkable increase of its reactivity. They allow the results of liquid-liquid extraction, precipitation and flotation reactions to be correctly interpreted and their changes to be foreseen when the reagents are modified. | 18,964,794 |
Preparation, composition and structure of some nickel and zinc ferrocyanides: Experimental results. | Several methods have been used for preparation of nickel and zinc ferrocyanides: precipitation, growth in a gel and a new method based on growth on a solid alkali-metal ferrocyanide. The granulometry, morphology, composition and structure of the compounds were studied. Only the last method of preparation gives products suitable for use as ion fixators in columns on a large scale. The nickel ferrocyanide compositions can be written as M(I)(2x)Ni(2-x)Fe(CN)(6).yH(2)O with M(I) Na, K, Cs, H and 0 < x < 0.8. They have a cubic lattice with a partial occupancy of iron sites. For zinc ferrocyanides, rhombohedral M(I)(2)Zn(3)[Fe(CN)(6)](2).xH(2)O, trigonal Zn(2)Fe(Cn)(6).2H(2)O and other cubic compounds were found. Products resulting from the fixation of caesium by ion-exchange were also studied. | 18,964,798 |
The uranyl-chloro-substituted benzoic acid-rhodamine b-benzene extraction system. | Of the chloro-substituted benzoic acids, the 2-chloro and 2,4-dichloro compounds yield higher effective molar absorptivities than benzoic acid does in the Rhodamine B-benzene extractive spectrophotometric procedure for determination of uranium(VI). Carbonyl compounds (especially acetone) in the organic phase enhance the extraction of the ion associate. The stoichiometry of the complexes has been determined, and a method of computing the extraction constants of the ion-associates developed. A spectrophotometric method for determining uranium in the presence of interfering ions has been designed. | 18,964,850 |
Stripping voltammetry of silver(I) with a carbon-paste electrode modified with thiacrown compounds. | The accumulation behaviour and stripping voltammetry of silver(I) was investigated with a carbon-paste electrode modified with a thiacrown compound. Silver could be accumulated at the electrode in the absence of an applied potential by immersing the electrode in a solution of sodium perchlorate containing silver(I), then reduced at constant potential in 0.1M acetate buffer solution. Finally a well-defined stripping peak could be obtained by scanning the potential in a positive direction. The calibration curve for silver was linear over the range 0.5-2.5 muM with accumulation for 5 min. Studies of the effect of other metal ions showed that the silver was selectively accumulated at the electrode. | 18,964,860 |
Adsorptive voltammetric determination of copper as its nioximate complex. | A sensitive and selective stripping voltammetric ultratrace determination of copper is described, based on adsorptive accumulation of the cu(II)-nioxime complex on the surface of a hanging mercury drop electrode, followed by the reduction of the adsorbed complex during the cathodic scan. The analytical conditions for the determination of copper by differential-pulse and linear-scan absorption voltammetry have been optimized. The method is compared to the routine anodic stripping voltammetric method for copper. Its applicability to river and potable water analysis is illustrated. The detection limit, restricted by the blank, is about 0.5 microg/l.; the relative standard deviation (at microg/l. level) for a standard solution is below 5% and for water samples is 5-9%. | 18,964,876 |
Effect of soluble calcium on the determination of the labile metal content of sediments with ion-exchangers. | Equilibration of sediments with cation-exchangers results in a transfer of loosely bound labile metal species to the exchanger phase. Dissolution of the matrix is also promoted and selectivity rules suggest that some of the cations released (particularly Ca) could effectively compete with metal ions for exchange sites. This potential source of error has been evaluated by studying synthetic mixtures of Ca(2+) and other metal ions (Cu(2+), Pb(2+), Cd(2+), Zn(2+)) and by analysis of two calcium-rich wastes (a calcine and a jarosite). The ion uptake most influenced by calcium competition was that of zinc; uptake of lead was least affected. For minimum error, i.e., optimum transfer of "available" or "labile" metal ion, the level of free Ca(2+) introduced into the solution should not exceed 300 mg/l., and the amount of exchanger added must provide an excess of exchange sites relative to the amount of cations released from the sample. By use of exchangers of different types it is possible to attempt some classification of the labile metal content, e.g., acid-displaced, exchangeable, salts of weak acids. | 18,964,894 |
Use of a spectrally segmented photodiode-array spectrometer for inductively coupled plasma atomic-emission spectroscopy Examination of procedures for the evaluation of detection limits. | The utility of a spectrally segmented photodiode array spectrometer was examined by using inductively coupled plasma atomic-emission spectrometry (ICP-AES). The spectrometer used in this study is capable of high resolution (reciprocal linear dispersion of approximately 0.08 nm/mm at 300 nm) over a wide spectral range (190-415 nm). The effect of using spectral peak areas instead of peak heights as a signal definition was examined by using the emission signals from 10 molybdenum lines obtained with various photodiode-array integration periods. In addition, a procedure to determine the detection limits obtainable with such a spectrometer is proposed. It was found that a signal definition involving a summation over a range of 5 pixels offered the best signal-to-noise ratio when the noise was defined as the standard deviation of the residual values from the line fitted to the sideband background level. A detection limit of 6 ng/ml was determined in this way for molybdenum. The multichannel capability of the spectrometer was found to permit continuous background correction, thereby reducing errors caused by low-frequency noise or plasma drift. The linearity of response was found to extend over three orders of magnitude with use of a single integration period. However, by use of different integration periods, the linear range of the detector could be extended to at least four orders of magnitude. The precision (RSD) of the spectrometer for a molybdenum concentration of 0.5 mug/ml was found to be about 3-4% for molybdenum peaks where the background emission was relatively low. | 18,964,913 |
Determination of tellurium in ores, concentrates and related materials by graphite-furnace atomic-absorption spectrometry after separations by iron collection and xanthate extraction. | A method for determining approximately 0.01 mug/g or more of tellurium in ores, concentrates, rocks, soils and sediments is described. After sample decomposition and evaporation of the solution to incipient dryness, tellurium is separated from > 300 mug of copper by co-precipitation with hydrous ferric oxide from an ammoniacal medium and the precipitate is dissolved in 10M hydrochloric acid. Alternatively, for samples containing 300 mug of copper, the salts are dissolved in 10M hydrochloric acid. Tellurium in the resultant solutions is reduced to the quadrivalent state by heating and separated from iron, lead and various other elements by a single cyclohexane extraction of its xanthate complex from approximately 9.5M hydrochloric acid in the presence of thiosemicarbazide as a complexing agent for copper. After washing with 10M hydrochloric acid followed by water to remove residual iron, chloride and soluble salts, tellurium is stripped from the extract with 16M nitric acid and finally determined, in a 2% v/v nitric acid medium, by graphite-furnace atomic-absorption spectrometry at 214.3 nm in the presence of nickel as matrix modifier. Small amounts of gold and palladium, which are partly co-extracted as xanthates if the iron-collection step is omitted, do not interfere. Co-extraction of arsenic is avoided by volatilizing it as the bromide during the decomposition step. The method is directly applicable, without the co-precipitation step, to most rocks, soils and sediments. | 18,964,927 |
Electrochemical behavior of marcellomycin at lipid-modified carbon-paste electrodes. | A lipid-modified carbon-paste electrode is prepared by mixing phospholipids with the carbon-paste matrix. The resulting electrodes have polar head-groups which allow interactions with positively charged drugs and improved preconcentration/extraction steps. The accumulation of the antitumor drug, marcellomycin, is enhanced in the presence of lipids, giving an 8-fold enhancement of current. The electrode response has been optimized with respect to paste composition, nature of the lipid, pH, temperature, and stirring time. A mechanism for marcellomycin accumulation is proposed, based on electrochemical and UV-visible spectrometric measurements as a function of pH. The electrode response is linearly related to the marcellomycin concentration within the range 1 x 10(-8)-6 x 10(-6)M. Known amounts of marcellomycin added to a urine sample diluted sixfold with water have been measured by use of the medium-exchange technique. | 18,964,932 |
A new spectrophotometric method for quantitative multicomponent analysis resolution of mixtures of salicylic and salicyluric acids. | A new spectrophotometric method for resolving binary mixtures is proposed. The method is based on use of the first derivative of the ratios of spectra. The absorption spectrum of the mixture is obtained and the amplitudes at appropriate wavelengths are divided by the corresponding amplitudes in the absorption spectrum of a standard solution of one of the components, and the first derivative of the ratio spectrum is obtained. The concentration of the other component is then determined from a calibration graph. The method has been applied for resolving binary mixtures of salicylic and salicyluric acids. Calibration graphs for 2.6-52 ppm salicylic acid and for 2.1-42 ppm salicyluric acid were established by measuring the analytical signals at the maximum at 241.5 nm (for salicylic acid) and from the peak at 258 nm to the trough at 247 nm (for salicyluric acid) in the first derivative ratio spectra. | 18,964,949 |
Elemental analysis of high-purity solids by mass spectrometry. | The applications of mass spectrometry in the determination of trace elements in some of the high-purity solid materials used in modern technology are reviewed. | 18,964,953 |
HPLC determination of niridazole. | A high-performance liquid chromatographic method has been developed for the determination of niridazole in bulk form and in pharmaceutical dosage form. A reversed-phase system, based on an octadecylsilane-bonded stationary phase and a 60:40 v/v methanol/water mobile phase, is used. The detector response at 370 nm is linearly related to the amount injected, over a wide range. The method is sensitive, simple, rapid and precise. | 18,964,970 |
Chelating polymers and related supports for separation and preconcentration of trace metals. | This review is concerned mainly with the applications of chelating polymeric resins for the separation and concentration of trace metals from oceans, rivers, streams and other natural systems. Commercially available resins, specially prepared polymers and a selection of other sorbents are described and their uses outlined. Special emphasis is placed on the preconcentration of uranium from sea-water. | 18,964,972 |
Heterocyclic dithiophosphates as analytical reagents Indirect extraction-spectrophotometric determination of silver in copper concentrates and ores. | The proposed method is based on the exchange reaction between the complex of copper(II) with 4,7-dimethyl-2-thiol-2-thion-1,3,2-dioxophosphorinan (DOPh(III)) in toluene and an aqueous solution of silver(I). The decrease in the absorbance of the Cu(DOPh(III))(2) solution is proportional to the silver(I) concentration for 5-90 mug of silver in 5 ml of toluene extract and 5-30 mug in 10 ml of toluene extract. The method is applied to the determination of silver in copper concentrates and ores. | 18,964,974 |
Computational studies of the chiral separations of three N-acyl-1-aryl-1-aminoethanes on an (R)-N-dinitrobenzoylphenylglycine stationary phase. | The chiral chromatographic separations of three N-acyl-1-aryl-1-aminoethanes on silica modified with (R)-N-dinitrobenzoylphenylglycine-N'-propylamide have been modeled by use of molecular mechanics. Formyl groups were substituted for the nitro groups, and a methyl group was tested as a replacement for the propyl group. With the propyl group, the correct elution order was obtained for the two pairs that had the largest alpha-values, and the third pair had a calculated alpha-value very close to unity. The relative sizes of the alpha-values were correctly predicted for all three. Substitution of methyl for propyl gave data that did not agree as well with the experimental values, thereby confirming the important role of the spacer in these separations. | 18,964,986 |
Spectrophotometric determination of trace sulphate in rain and snow after preconcentration with 2-aminoperimidine on a membrane filter. | A simple and precise preconcentration technique, based on collecting a precipitate on a membrane filter and dissolving the filter and precipitate in an organic solvent, has been applied to the spectrophotometric determination of trace sulphate in rain and snow. The sulphate is precipitated with 2-aminoperimidine and the resulting compound is dissolved in nitric acid, made alkaline with sodium hydroxide and then adsorbed on tetradecyldimethylbenzylammonium nitrate. The precipitate is then collected on a membrane filter and both precipitate and filter are dissolved in dimethylsulphoxide (DMSO). The absorbance of the DMSO solution is measured at 550 nm against a reagent blank. The molar absorptivity is 2.1 x 10(4) 1 . mole(-1) . cm(-1) and the coefficient of variation for six measurements is < 1.5%. The detection limit (S/N = 3) is 0.06 mug of sulphate in 5 ml of sample solution. | 18,964,991 |
A study of electrodes used in controlled-potential electrolysis of metal ions. | Various electrodes used in controlled-potential electrolysis of metal ions are discussed: (1) a double-junction saturated calomel reference electrode with sodium formate as bridge electrolyte; (2) an auxiliary electrode made by winding platinum wire on a Teflon cylinder; (3) a working electrode made of tantalum gauze. The advantages of the tantalum electrode over a platinum electrode are that the hydrogen overpotential is higher, and the tantalum electrode need not be precoated with copper before deposition of metals such as Bi, Zn and Sn, which tend to form alloys with platinum. The electrode needs pretreatment before use, but this takes only 4 min or less. | 18,965,001 |
A review of pH measurement at high temperatures. | Measurement of pH in aqueous solutions at up to 300 degrees and 150-300 bar is reviewed. Potentiometric membrane electrodes are identified as the sensors giving the most immediate hope of being practical. Zirconia membranes work well above 200 degrees and in alkaline solution, whereas glass membranes are best up to 150 degrees and in acidic solutions. Both membranes are largely free from interferences. Metal-metal oxide electrodes offer poor prospects, deviating from the ideal Nernstian response at all temperatures and being susceptible to interference from many redox and complexing agents, but systems based on iridium oxide have some promise. The hydrogen electrode remains the standard for pH measurement, but its analytical application is limited by the need to know the hydrogen partial pressure. A practical solution to this problem has yet to be found, except in restricted and artificial circumstances. Palladium hydride electrodes may be useful up to about 200 degrees , but in hydrogen-saturated waters revert to being hydrogen electrodes in any case. Non-potentiometric pH measurements with semiconducting oxides have been shown to be possible, but there are many unanswered questions about possible interferences. Considerable extra instrumentation is required, compared with potentiometry. Fibre-optic sensors based on indicator dyes have been investigated at room temperature, and have the great merit of not requiring a reference electrode. They seem, however, prone to many interferences and have an inherently limited working range of approximately 2 pH. No measurements at high temperature have been reported. Improved reference electrodes for potentiometric systems are still needed, although there have been advances in the design of external pressure-compensated electrodes working at room temperature. The silver-silver chloride system is still the one most favoured. There has been little rigorous work on standard buffer solutions at above 100 degrees and none at above 200 degrees . Neutral and alkaline buffers are especially needed. The establishment of proper pH standards for high-temperature work would make the testing of sensors both speedier and more reliable. Doubtless because of the experimental difficulties involved, few measurements have actually been made at high temperature, and those in a rather restricted range of conditions. In particular, measurements in dilute, poorly buffered, solutions, which provide the most rigorous test of a system's capability, are completely lacking. | 18,965,019 |
Trace measurements of colchicine by adsorptive stripping voltammetry. | A highly sensitive voltammetric method for trace measurements of the alkaloid colchicine is described. The method is based on the controlled adsorptive accumulation of the drug at the hanging mercury drop electrode, followed by voltammetric determination of the surface species. The adsorptive stripping response is evaluated with respect to preconcentration time and potential, solution pH, voltammetric waveform and other variables. With a 10-min preconcentration, a detection limit of 1.3 x 10(-10)M is obtained. The relative standard deviation (at the 1 x 10(-7)M level) is 1.1%. Applicability to urine analysis is illustrated. | 18,965,020 |
Voltammetric determination of linuron at a carbon-paste electrode modified with sepiolite. | The determination of linuron by differential pulse voltammetry with a carbon-paste electrode modified with 20% w/w sepiolite has been studied. The linuron is preconcentrated under open-circuit conditions at pH 2.0. With 0.01M potassium nitrate at pH 1.7 in the measurement cell, a sweep rate of 30 mV/sec and a pulse amplitude of 100 mV, an oxidation wave with a peak potential of 1.2 V is obtained. Under these conditions, determination limits of 75 ng/ml have been obtained, with a relative error of +2.8% and a relative standard deviation of 8.0%. The method has been applied to the direct determination of linuron in river water with no previous separation of the pesticide. Determination in sea-water is not possible, as chloride interferes at high concentration. | 18,965,021 |
An amperometric enzyme electrode for the determination of 3alpha-hydroxysteroids. | An enzyme electrode for quantifying the total content of 3alpha-hydroxysteroids is described. 3alpha-Hydroxysteroid dehydrogenase (E.C. 1.1.1.50) was immobilized on the surface of glassy-carbon and low-temperature isotropic-carbon electrodes by intermolecular cross-linking with bovine serum albumin and glutaraldehyde. The effects of the following factors on the response to androsterone were studied: applied potential, the concentration and pH of the pyrophosphate buffer used, and the NAD concentration. The Michaelis-Menten constant for 3alpha-hydroxysteroid dehydrogenase in solution was determined amperometrically with androsterone as substrate (K(m) = 189muM). A preliminary report of the response of the system to serum samples containing a bile acid is presented. | 18,965,022 |
Spectrophotometric determination of some dithiocarbamates. | A procedure has been developed for the determination of six dithiocarbamates [sodium dimethyldithiocarbamate (dibam), sodium diethyldithiocarbamate (NaDDC), tetramethylthiuram disulphide (thiram), zinc dimethyldithiocarbamate (ziram), sodium N-methylpiperazinecarbodithioate and potassium morpholine-4-carbodithioate] in microgram quantities by converting them into selenium dithiocarbamate complexes, which are then extracted into chloroform and measured at 430 nm against a reagent blank. The method is sensitive and can be used for the determination of dithiocarbamates in commercial samples and synthetic mixtures. | 18,965,097 |
Microband electrodes fabricated by screen printing processes: Applications in electroanalysis. | A novel method for the simple and cheap manufacture of microband and multiple microband electrodes is described. The construction technique is based entirely on the screen printing of the surface of alumina tiles with conducting and insulating ink materials. The range of potentials over which the electrodes may be used has been determined by basic electrochemical studies. These electrode systems have been used successfully for the measurement of vitamin C, vitamin B(1) and paracetamol, which illustrates, their potential as useful tools in the field of electroanalysis. | 18,965,101 |
Amperometric detection at a carbon-fibre array ring/glassy-carbon disk electrode in a wall-jet cell. | A wall-jet cell incorporating a carbon fibre array ring/glassy-carbon disk electrode has been constructed, and characterized by the cyclic voltammetry and flow-injection techniques. The ring (composed of several microdisks) and glassy-carbon disk electrode, can be used separately for different purposes, e.g., detection in solution without a supporting electrolyte, collection/shielding detection with dual-electrode and voltammetric/amperometric detection with series dual-electrode. The electrode shows better collection and shielding effects than the usual ring-disk electrode in quiescent solution and the series dual-electrode in a thin-layer flow-through cell. The detection limit at the ring electrode is comparable with that at a conventional-size electrode, and has been used in the mobile phase without a supporting electrolyte, proving to be a promising detector for normal-phase liquid chromatography. | 18,965,107 |
On-line photo-oxidation for the determination of organoarsenic compounds by atomic-absorption spectrometry with continuous arsine generation. | A method has been developed for on-line conversion of organoarsenicals into arsenate, which is readily detected by atomic-absorption spectrometry with continuous arsine generation. The photoreactor consists of a mercury lamp wrapped with 5 m of PTFE tubing (0.5 mm i.d.). The photo-oxidation conditions were optimized, with a flow-injection analysis procedure, for arsenobetaine, monomethylarsonic acid, dimethylarsinic acid, o-arsanilic acid, and phenylarsonic acid, all organoarsenicals of biological and environmental importance. Solutions were continuously pumped at a flow-rate of 2.0 ml/min and combined with a stream of potassium persulfate (flow-rate 0.6 ml/min) before entering the photo-reactor. With reactor dwell times of 36 sec, conversion efficiencies for these compounds were above 95% under these conditions. Interfacing of this flow-through conversion and detection system with a chromatographic inlet permits real-time analysis of mixtures of these organoarsenic compounds, in a manner suitable for environmental or biomedical samples. | 18,965,123 |
On-line monitoring of chloramine reactions by membrane introduction mass spectrometry. | Membrane introduction mass spectrometry has been applied to on-line monitoring of the reaction of monochloramine with hydrogen chloride. The detection limit for monochloramine introduced by a sheet-membrane direct-insertion probe and measured by electron impact ionization and selected ion detection was found to be 0.7 mg/l. Formation of dichloramine, trichloramine and molecular chlorine in response to the addition of hydrogen chloride to the monochloramine solution was measured on-line. The flow-through membrane introduction mass spectrometry method for detection of chloramines and characterization of their chemistry has minimal memory effects, high molecular specificity, high speed of analysis owing to fast response times, and low detection limits. | 18,965,127 |
Spectrophotometric determination of nickel in vegetable oil with ammonium 2-amino-1-cyclohexene-1-dithiocarboate. | The reaction between nickel and ammonium 2-amino-1-cyclohexene-1-dithiocarboate in aqueous acetone medium at pH 3.0-8.0 results in a stable dark red complex. The ratio of reagent to nickel in the complex is 2:1 and the formation constant is 7.38 +/- 0.12 x 10(10). Beer's law is obeyed up to 4 microg/ml nickel at the absorption maximum at 535 nm. The apparent molar absorptivity is 2.8 x 10(4) l.mole(-1). cm(-1), and the detection limit is 10 ng/ml nickel. The method is applied to the determination of nickel in vegetable oil. | 18,965,133 |
X-ray powder diffraction data for nine analgesics. | X-Ray powder diffraction data for nine analgesics have been obtained by using a powder diffractometer. The results obtained by using the McCreery and Byström-Asklund methods of sample loading were averaged and tabulated in terms of the lattice spacings and the relative line intensities. Data from powder camera films were compared with the diffractometer data, and certain discrepancies in the intensities are discussed. | 18,965,134 |
Determination of aminosaccharides by high-performance anion-exchange chromatography with pulsed amperometric detection. | High-performance anion-exchange chromatography (HPAC) was used for the determination of aminosaccharides in microbial polymers, chitin, animal waste, sewage sludge, plant residues and soil. The aminosaccharides, galactosamine, mannosamine and glucosamine were separated on a strong anion-exchange column with 1OmM sodium hydroxide as the eluent and determined by pulsed amperometric detection (PAD). The HPAC-PAD methodology was compared with high-performance liquid chromatography (HPLC) with refractive index detection (RI) in terms of selectivity and sensitivity for aminosaccharides. The results indicate that HPAC-PAD required less sample preparation, and was more precise and nearly two orders of magnitude more sensitive than HPLC-RI. HPAC-PAD was not subject to matrix interferences and was highly selective for aminosaccharides. More than 3% of the total nitrogen in alfalfa, and 20% of that in straw, was found to be present as aminosaccharides. | 18,965,136 |
Determination of metal ions by liquid chromatographic separation of their 2-acetylpyridine-4-ethyl-3-thiosemicarbazone chelates. | A new thiosemicarbazone was prepared, characterized, and used as a complexing reagent for the chromatographic separation and determination of metal complexes by reverse-phase HPLC. The reagent was sufficiently soluble in methanol-water solutions for metal ions to be complexed in this aqueous organic phase, without need for extraction. Many variables affected the retention times of the metal complexes. Several metals were determined selectively by complexation with the reagent and chromatographic separation of the complexes. Interference effects from other metal ions were also investigated. | 18,965,137 |
Accuracy in the precise coulometric titration of ammonia and ammonium ion with electrogenerated hypobromite. | A precise and accurate method in which ammonia and ammonium ions are coulometrically titrated with electrogenerated hypobromite was studied. Through the measurement of the current efficiency for generating hypobromite and the dependencies of titration results on electrolysis current and delay time between sampling and starting electrolysis, precision and accuracy of 0.01 and 0.02%, respectively, were obtained. The accuracy of the titration was compared with that of acidimetric coulometric titration of ammonia. | 18,965,161 |
Trace measurements of rhodium by adsorptive stripping voltammetry. | A sensitive stripping voltammetric procedure for quantifying rhodium is described. The complex of rhodium with chloride ions is adsorbed on the hanging mercury drop electrode, and the reduction current of the accumulated complex is measured during a negative-going scan. Cyclic voltammetry is used to characterize the interfacial and redox behaviors. The effect of pH, chloride concentration, accumulation potential and other variables is discussed. The detection limit is 1 x 10(-8)M ( approximately 1 ng/ml) with 5-min accumulation. A linear current-concentration relationship is observed up to 7 x 10(-7)M and the relative standard deviation (at the 2 x 10(-7)M level) is 3.0%. Possible interferences by co-existing metals are investigated. | 18,965,175 |
The synthesis of some lipophilic tetra-arylborates for use in membrane electrode preparation. | Synthetic methods for preparing four lipophilic tetra-arylborates considered suitable candidates for use in membrane electrodes are described. Qualitative precipitation tests were performed with several cations. The sodium salts of the four tetra-arylborates were found to have limited stability but the cesium salts were relatively stable. | 18,965,176 |
Determination of cadmium, lead and copper in water samples by flame atomic-absorption spectrometry with preconcentration by flow-injection on-line sorbent extraction. | Cadmium, lead and copper were determined in synthetic sea-water, drinking water and the NBS 1643b Trace Elements in Water standard reference material at mug/l. levels by flame atomic-absorption spectrometry after on-line preconcentration by sorbent extraction with a flow-injection system. Bonded silica with octadecyl functional groups packed in a micro column of 100 mul capacity was used to collect diethylammonium diethyldithiocarbamate complexes of the heavy metals in the aqueous samples. The sample loading time was 20 sec at a flow-rate of 3.3 ml/min. Ethanol or methanol was used to elute the adsorbed analytes into the spectrometer. The sample loading rate, elution rate and pH were optimized. Enrichment factors of 19-25 for Cd, Pb and Cu were achieved at sampling frequencies of 120/hr with precisions of 1.4, 1.0 and 1.3% rsd (n = 11), respectively. The detection limits (3sigma) for Cd, Pb and Cu were 0.3, 3 and 0.2 mug/l., respectively. Determination of Cd, Pb and Cu in NBS SRM 1643b showed good agreement with the certified values. Recoveries of Cd and Pb added to sea-water were 95 and 102%, respectively. | 18,965,193 |
Catalytic kinetic determination of ultratrace amounts of ruthenium(III) based on the oxidation of benzylamine by alkaline hexacyanoferrate(III). | A kinetic method is proposed for the determination of ruthenium(III) by means of its catalytic effect on the oxidation of benzylamine by hexacyanoferrate(III) in alkaline medium. The reaction is followed spectrophotometrically by measuring the decrease in the absorbance of hexacyanoferrate(III) at 420 nm. Under the optimum experimental conditions ruthenium(III) can be determined in the range 10-121 ng/ml with an average error of 1.7% and maximum relative standard deviation of 1.3%. The influence of many potential interferents has been examined and the method has been tested for determination of ruthenium(III) in synthetic mixtures. The method is convenient, reliable and rapid. | 18,965,195 |
On the application of the Dumas technique for the determination of nitrogen in refractory nitrides. | The classical Dumas apparatus has been modified. The generally recommended oxidants CuO and V(2)O(5), were found to give relatively high blank values and were therefore replaced by Cu(2)O. The preparation of the Cu(2)O is described. It is an exceptionally suitable oxidant for the Dumas analysis of the Group Va nitrides as well as manganese nitrides and molybdenum nitrides because it does not release oxygen into the gas phase. The reaction of the Group IVa nitrides as well as of CrN with CuO and Cu(2)O is, however, not completely quantitative at 1000-1150 degrees in reasonable reaction times. The results of the Dumas analysis of a Group IVa nitride should be corrected by measuring the nitrogen content of the residue (e.g., by hot extraction). The relative standard deviations do not exceed 0.38%. The nitrogen contents (% w/w) of the residues range from <0.001% for Mo(2)N + MoN to 0.54% for Cr(2)N + CrN. BN, Si(3)N(4) and AlN could not be decomposed with copper oxides under the conditions used. AlN could be analysed by adding V(2)O(5), but the rsd was 0.55% and the nitrogen content in the residue was 0.52% w/w. Neither BN nor Si(3)N(4) could be analysed by addition of V(2)O(5). | 18,965,201 |
Kinetic determination of selenium, based on inhibition of the Pd(II)-catalysed reaction between pyronine G and hypophosphite. | A new kinetic method for determination of selenium is based on its inhibitory effect on the Pd(II)-catalysed reaction between Pyronine G and hypophosphite. Under the optimum experimental conditions (6 x 10(-5)M Pyronine G, 0.4M hypophosphite, 0.4 mug/ml Pd(II), pH 2.8, temperature 22.0 +/- 0.2 degrees ), Se can be determined in the concentration range 0.033-0.50 mug/ml. The method suffers from numerous interferences and is thus limited in application. It has been applied to the determination of selenium in spring waters and pharmaceutical preparations. | 18,965,205 |
Determination of molybdenum by atomic-absorption spectrometry after separation by 5,5'-methylenedisalicylohydroxamic acid extraction and further reaction with thiocyanate and tin (II). | A method is described for the determination of molybdenum down to the microgram level, in samples of soil, steels, fertilizers and pharmaceuticals. After attack with acids, this element is separated from matrix elements by extraction of its 5,5'-methylenedisalicylohydroxamic acid (MEDSHA) complex from 4M hydrochloric acid, into methyl isobutyl ketone. Molybdenum is determined by atomic-absorption spectrometry (AAS), after conversion of the Mo-MEDSHA complex into the MoSCN(-) complex in the organic phase. The detection limit is 0.03 microg/ml, with a relative standard deviation not exceeding 1.5% at a level of 2 microg/ml. The method is highly selective and suffers only from interference by tungsten. | 18,965,215 |
Determination of copper at ng levels by in-line preconcentration and flow-injection analysis coupled with flame atomic-absorption spectrometry. | Oxine/formaldehyde/resorcinol and oxine/formaldehyde/hydroquinone resins have been synthesized and their physicochemical properties studied. Conditions were optimized for the preconcentration of copper by batch extraction and column chromatography with the resins. A flow-injection analysis (FIA) manifold was constructed for the determination of copper at ng levels by preconcentration on microcolumns containing the resins, stripping, and atomic-absorption spectrometry. For batch preconcentration a pH of about 2.5-3 was optimal whereas in the FIA system a broader pH range (approximately 2-3.5) could be used. Separations of binary mixtures of Cu(II) with Ni(II) or PB(II) at microg/ml level did not show any cross-contamination. In the FIA, a 2 cm long column and 2 ml/min flow-rate were adequate for quantitative uptake of copper; 50 micro1 of 0.1M hydrochloric acid quantitatively eluted the copper. | 18,965,216 |
A highly sensitive colour reaction for chromium(VI) with the iodide-basic xanthene dye-pva system. | A highly sensitive spectrophotometric method has been developed for determination of chromium(VI), based on oxidation of I(-) to I(-)(3) in acid medium, then formation of a 1:1 ion-association compound of I(-)(3) with a basic xanthene dye in the presence of poly(vinyl alcohol). The molar absorptivity is 1.79 x 10(5) 1.mole(-1).cm(-1) at 600 nm for the Rhodamine B system, 1.56 x 10(5) 1.mole(-1).cm(-1) at 600 nm with Ethylrhodamine B, 1.56 x 10(5) 1.mole(-).cm(-1) at 570 nm with Rhodamine 6G and 2.01 x 10(5) 1.mole(-1).cm(-1) at 590 nm with Butylrhodamine B, respectively. Preconcentration of chromium(VI) by an improved trioctylamine extraction procedure greatly increases the selectivity of the method and can be applied in the spectrophotometric determination of trace amounts of chromium(VI) in tap water, hot-spring water and river water. | 18,965,224 |
Comparative study of a beenakker cavity and a surfatron in combination with electrothermal evaporation from a tungsten coil for microwave plasma optical emission spectrometry (MIP-AES). | Microwave induced plasmas, sustained in a Beenakker resonator and a surfatron, respectively, are used to excite vapours released by electrothermal evaporation of solutions from a tungsten coil. The analytical figures of merit of AES for two easily volatilized elements (Cu, Cd) are compared for argon MIP operated in the two resonators under optimized conditions. In the Beenakker resonator a 1-filament plasma was produced at an argon flow of 0.45 l./min and a forward power of 50 W. In the surfatron a 2-filament plasma with 2.44 l./min argon and a forward power of 130 W was used. The detection limits for Cu and Cd with the surfatron are lower than those obtained with the Beenakker resonator and are in the range 10-20 ng/ml. Also interferences arising from an easily ionized element such as Na are lower with the surfatron than with the beenakker resonator. The linear dynamic ranges in the case of the surfatron are also superior and extend over three decades of concentration. | 18,965,230 |
The determination of lead in total suspended air particulates by x-ray fluorescence spectroscopy. | A method has been developed for the measurement of lead in air particulates collected on glass fiber filter paper with wavelength-dispersive x-ray fluorescence spectroscopy (WDXRF). Analyses conducted by both WDXRF and an EPA-approved procedure that employs acid sonication followed by analysis of the extract by atomic-absorption spectroscopy (AAS) shows excellent agreement between the two methods. WDXRF calibration was accomplished with standards prepared from known additions of Pb to unexposed glass fiber filter discs. Method equivalency has also been demonstrated by the analysis of several reference materials and the statistical analysis of quality control data. The WDXRF procedure has also been used to evaluate the distribution of Pb in the particulates across the surface of the filter. | 18,965,250 |
Simultaneous determination of iron(III) and vanadium(V) by use of a kinetic-spectrophotometric and rapid mixing flow system. | The quantitative spectrophotometric determination of V(V) by its catalytic effect on the oxidation of chromotropic acid [the disodium salt of 4,5-dihydroxynaphthalene-2,7-disulphonic acid (CS)] by potassium bromate has been adapted to a flow system employing a rapid sample and reagent introduction manifold, in which valves and carrier streams are omitted without decreasing the precision or increasing the sample consumption relative to flow-injection analysis (FIA). Measurements are made at 420 nm. Coexisting Fe(III) can be determined simultaneously at the same wavelength by its more rapid colour chelate formation with CS. An accurate determination of V(V) and Fe(III) in the mixture was developed with a sample throughput of about 60 hr. | 18,965,277 |
Potentiometric determination of trace silver based on the use of a carbon paste electrode. | A carbon paste electrode used as a sensor for silver has been developed and electrode response characteristics have been investigated. The electrode exhibits linear response to the logarithm of the concentration of silver from 5 x 10(-7)M to 1 x 10(-2)M, with a response slope of 63 +/- 2 mV. The detection limit according to IUPAC recommendations is 1 x 10(-7)M. This electrode has been used to determine trace silver in fixing solutions and waste electroplate solutions with good results. | 18,965,282 |
Statistical optimisation applied to the spectrophotometric study of the tolmetin-Fe(III) complex. | Tolmetin sodium has been examined and determined from dosage forms as its Fe(III) complex and the method has been optimized by statistical optimization. | 18,965,308 |
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