title stringlengths 0 1.13k | abstract stringlengths 1 15.7k | PMID int64 22 36.5M |
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Determination of indium by hydride generation and atomic-absorption spectrometry. | Conditions are presented for the determination of indium by atomic-absorption spectrometry following hydride generation. Indium hydride produced by addition of sodium borohydride to a solution of indium in 3M hydrochloric acid is flushed with argon into an electrically heated silica tube. The mass of indium giving 1 % absorption is 0.3 mug. | 18,963,177 |
Effect of cationic surfactant on the formation of ferron complexes. | In the spectrophotometric determination of aluminium and iron with ferron (7-iodo-8-quinolinol-5-sulphonic acid, H(2)L), the addition of cationic surfactants greatly improves the linearity of the calibration curve and widens the useful pH range. The effect of cetyltrimethylammonium chloride (CTMAC) on the stepwise stability constants (K(1),K(2) and K(3)) of the ferron complexes of aluminium and iron (ML(+), ML(-)(2) and ML(3-)(3)) and on the acid-dissociation constants (K(a1) and K(a2)) of ferron has been studied in connection with the role of the surfactant. CTMAC greatly increases the value of K(3) while exerting little effect on K(1) and K(2), thus rendering ML(3-)(3) the predominant species even at very low concentration of free L(2-). It also has some effect on the acid-dissociation constants of ferron, but sometimes it acts to decrease the free L(2-) concentration. At is therefore concluded that the improvements due to addition of surfactant should be attributed to the increased K(3) value. The presence of surfactant micelles is not essential, because the surfactant has a favourable effect when present at well below its critical micelle concentration, and because the continuous variations plots show a peak at a point corresponding to the composition M: L: Q (Q = cationic surfactant) = 1:3:3. | 18,963,188 |
Determination of molybdenum by extraction of its thiocyanate into ethyl methyl ketone. | A simple, sensitive and selective spectrophotometric method for determination of molybdenum is described. A solution containing 100 mug of Mo in 2.5M hydrochloric acid is treated with ascorbic acid and ammonium thiocyanate and after standing for 8 min is shaken with an equal volume of ethyl methyl ketone for 30 sec. The absorbance of the complex is measured at 465 nm against a reagent blank. The complex is stable for 1 hour. There is no interference from Re(VII), SO(2-)(4), Cl(-), CH(3)COO(-), PO(3-)(4), NO(-)(3), C(2)O(2-)(4), citrate or tartrate, and at least 5 mg of U(VI), 10 mg of Cr(III, VI), Th, or Ni, and 20 mg of W(VI) Can be tolerated. Vanadium(V) interferes at the 500 mug level, and fluoride slightly decreases the absorbance. | 18,963,196 |
Selective extraction of metal ions associated with humic acids. | The ability of a range of electrolyte solutions to release metal ions (Cu, Pb, Cd, Zn) presorbed on two samples of humic acid has been investigated. Though treatment with mineral acid or a chelating agent released a high proportion of the retained metal ion, recoveries were never total. Concentrated salt solutions displaced about 80% of the retained Cd or Zn, and about half of any Cu or Pb held by the organic matter, which indicates that most of the adsorbed metal ion is exchangeable, the extraction efficiency being controlled by competing equilibria. The effect of added clay suspensions was also examined. Analytical procedures for fractionating the total metal content of soils into subgroups have been assessed against the observed extraction behaviour. | 18,963,227 |
Validation of the sulphur concentration of selected iron-base NBS standard reference materials by isotope-dilution spark-source mass-spectrometry. | An isotope-dilution spark-source mass-spectrometric procedure has been developed for the accurate determination of sulphur in iron-base alloys. Dissolution in a sealed tube is used to prevent volatilization losses and to effect isotope equilibration. Application of this technique to the re-analysis of existing NBS Standard Reference Materials yields results that are generally in good agreement with the certified values. | 18,963,243 |
Biacetyl monoxime glycinimine as a selective reagent for palladium and nickel. | Biacetyl monoxime glycinimine is proposed as a new reagent for the selective gravimetric and extractive photometric determination of Pd(II) and Ni(II). The reagent forms yellow and rose-red water-insoluble complexes with Pd (pH 0.5-5.5) and Ni (pH 5.0-11.2) respectively. The complexes can be used for direct gravimetric determination or extracted with molten naphthalene. The solidified naphthalene-complex mixture is dissolved in chloroform and measured photometrically. The effects of experimental variables and diverse ions are reported. The proposed reagent offers better selectivity than dimethylglyoxime. | 18,963,268 |
Purification of analytical reagents. | Considerable progress in the purification of reagent chemicals has been made during the past decade. Improved or newly developed methods and their application for producing analytical reagents of highest purity are described. Various techniques are evaluated critically with respect to convenience and efficiency of use in the trace analysis laboratory. | 18,963,277 |
[Not Available]. | This paper describes a low-cost 6809 microprocessor-based system designed for the acquisition, analysis, preprocessing and recording of electrochemical kinetic data. Determination of second-order rate constants involves a preliminary calculation of a characteristic parameter of the electro-chemical system investigated, the value of which, computed and displayed by our apparatus, allows checking of the correctness of the experimental conditions. At the end of the experiment the data are recorded on a magnetic tape cartridge and can be transferred from the tape to a minicomputer for further mathematical processing. | 18,963,289 |
Elution and spectrophotometric determination of gold after its separation from non-volatile platinum metals by column extraction chromatography. | Mixtures of gold(III) and iridium(IV) were separated by column extraction chromatography on silica treated with a tri-n-octylamine (TOA) salt. A mixture 2.25M in hydrochloric acid and 5M in nitric acid was used for elution of iridium. Gold was eluted together with the TOA salt by acetone, and after evaporation of the acetone, the TOA chloroaurate was dissolved in chloroform, converted into TOA bromoaurate and determined spectrophotometrically at 395 nm ( = 3.4 x 10(3) l.mole(-1) .cm(-1)). Beer's law was obeyed over the concentration range 5-67 ppm of gold. The method was found suitable for determination of gold after its separation from other metals by extraction chromatography on supports treated with liquid anion-exchangers. | 18,963,301 |
Iodometric standardization and biamperometric determination of iridium(IV). | Ir(IV) in the concentration range 0.4-0.8 g/l. can be easily determined iodometrically with 0.01M thiosulphate (starch as indicator). The relative standard deviation is 0.2-0.3%. When other coloured ions are present, biamperometric detection is recommended. | 18,963,305 |
Silica gel with adsorbed Adogen 464 as an analytical sampling tool for anions. | A solid extractant made with the liquid anion-exchanger Adogen 464 supported on silica gel has been prepared and its potential as a resin-like exchange material has been evaluated. In acid media it furnishes a ready available, inexpensive tool for recovery of anionic metal complexes as well as simple anions and for elimination of complex matrices. Copper and cobalt have been recovered (with a concentration factor of 20) from sea-water, natural water, metal alloys and industrial electroplating baths and measured by atomic-absorption spectrophotometry. The detection limits for copper and cobalt are 0.2 and 0.4 ng ml respectively and interferences are minimal. Chromium(VI) has been separated from chromium(III), and a concentration factor of 40 and a detection limit of 0.2 ng ml have been achieved. | 18,963,310 |
An algorithm for reducing storage requirements in computer calculation of chemical equilibria. | An algorithm for storage of stoichiometric coefficients of the possible complexes and solids in a multi-component system of metals and ligands is described, along with FORTRAN code for its implementation. The proposed algorithm results in considerable saving in storage over the conventional use of a two-dimensional array. The saving in storage is especially useful for microcomputers, and for very large problems such as those encountered in geochemical calculations. | 18,963,319 |
Determination of silicon by an indirect atomic-absorption method using carbon-rod electrothermal atomization. | An indirect procedure has been developed for the determination of trace amounts of silicon by atomic-absorption with carbon-rod electrothermal atomization. After dissolution, the silicon is extracted as silicomolybdic acid into a mixture of diethyl ether and pentan-1-ol (5 + 1). The co-extraction of excess of molybdate reagent is prevented by the addition of citrate, which also destroys phosphomolybdic and arsenomolybdic acids. The organic layer is washed with hydrochloric acid, mul quantities are transferred to the electrothermal atomizer and the molybdenum is measured. The method has been applied to analysis of several steels. | 18,963,328 |
Chemical and instrumental analysis of ferrites. | More than thirty years since the manufacture of the first commercial ferrites, research and development efforts continue to produce ferrites with enhanced performance and new applications. Analytical chemistry has maintained a substantial role in the ferrite industry in the characterization of both raw materials and products, and the analytical literature of ferrites has grown accordingly. The continuing importance of ferrites to the electronic device industry requires further development of analytical methods suitable for characterization of ferrites so that their chemical composition may be related to performance and to the manufacturing processes used. As modem analytical techniques have been developed, their application to the characterization of ferrites and the detection of heterogeneity in these materials is increasing. | 18,963,365 |
Spectrophotometric determination of trace amounts of selenium with 4,5,6-triaminopyrimidine. | 4,5,6-Triaminopyrimidine reacts in acidic aqueous media with selenium (IV) to give a piazselenol which has an absorption maximum at 362 nm with a molar absorptivity of 1.72 x 10(4) 1.mole(-1).cm(-1). The compound is stable but not extractable into non-polar solvents. The calibration graph is linear up to 10 ppm of selenium, with a detection limit of 0.1 ppm in the sample solutions. Of the many different ions tested only iron (III) (in the presence of chloride) and tin (II) interfere. The method has good reproducibility, with a relative standard deviation of 1.5% for pure solutions. The application of this method to analysis of water and electrolytic copper is described. | 18,963,385 |
Application of cellulose anion-exchangers to separation of palladium from platinum or iridium with glycine as complexing agent and atomic-absorption spectrometry for detection. | The use of glycine as complexing agent for chromatographie separation of palladium from platinum, or palladium from iridium, on cellulose anion-exchangers has been investigated and found possible over a wide range of concentration ratios. The method can be used for analysis of Pd-Ir alloys. The nature of the complexes taking part in the ion-exchange has been identified. | 18,963,400 |
Titrimetric microdetermination of uric acid and thioglycollic acid by amplification reactions. | A simple amplification method for determination of 0.05-2 mg of uric acid or thioglycollic acid has been worked out. It depends on iodine oxidation of the uric acid or thioglycollic acid solutions, removal of the excess of iodine, oxidation of the resulting iodide with bromine, and iodometric titration of the resulting iodate. The coefficient of variation ranges from 0.7 to 2.4% for uric acid and from 0.5 to 1.9% for thioglycollic acid, depending on the amount of the acid. | 18,963,429 |
Selective complexometric determination of mercury with thiocyanate as masking agent. | A method is proposed for selective complexometrie determination of mercury, thiocyanate being used as masking agent. An excess of EDTA is added and the surplus is back-titrated at pH 5-6 with lead nitrate, Xylenol Orange or Methylthymol Blue being used as indicator. Thiocyanate is then added to decompose the mercury-EDTA complex and the liberated EDTA is titrated with lead nitrate. The interference of various cations has been studied. | 18,963,430 |
Rapid and selective chelatometric titration of zinc in non-ferrous alloys. | A rapid titrimetric method for the determination of Zn (5%) in zinc, aluminium and copper alloys is proposed. It is based on the chelation of Zn(II) with HEDTA as titrant in an ethanolic aqueous medium. The end-point is detected with hydrazidazol, a new indicator developed in China. Up to at least 6% Mn in the alloy does not interfere. Direct determination of Zn(II) is rendered possible by using a combination of masking agents. A separation is needed only if nickel is also present. A decided advantage of this method is its high selectivity. The standard deviation was found to be 0.07 mg and the coefficient of variation to vary from 0.2 to 0.5%. The method has been successfully used to determine Zn in different kinds of non-ferrous alloys, especially those containing Mn. | 18,963,480 |
Solid-state halide ion-selective electrodes: studies of quaternary ammonium halide solutions and determination of surfactants. | The feasibility of using homogeneous membrane-type halide ion-selective electrodes in solutions containing cationic surfactant compounds was examined. The results established the applicability of these electrodes for monitoring halide ions in solution without interference by the surfactants. The data also provided a basis for estimation of the surfactant in solution through the halide content. Two typical plating-bath compositions containing CTAB have been successfully analysed for their surfactant content by this procedure. | 18,963,482 |
Determination of thallium in lead salts by differential pulse anodic-stripping voltammetry. | The determination of trace levels of thallium in lead and lead salts by differential pulse anodic-stripping voltammetry has been made possible by using a surfactant as an electrochemical masking agent in addition to a complexing agent. In 0.2M EDTA at pH 4.5 as supporting electrolyte without surfactant, lead at concentrations below 0.5mM does not give a peak. When the electrolyte also contains tetrabutylammonium chloride (TBAC) at 0.01 M concentration, lead can be tolerated at concentrations up to 0.05M, while the height of the thallium peak is unaffected. It is thus possible to determine 5nM T1(I) in the presence of 0.05M Pb(II), i.e., Tl at the 1 x 10(-5)% level in lead. The precision of the determination (1-4%) and the recovery are satisfactory. Neither an 800-fold excess ratio of Cu(II) to Tl(I) nor a 10(7)-fold ratio of Bi(III) interferes in the determination. Thallium has been determined in a range of lead salts of various degrees of purity. | 18,963,486 |
Critical examination of some common reagents for reducing selenium species in chemical analysis. | In an attempt to resolve apparently conflicting statements in the literature, a study has been made of the action of various reductants on selenium(VI) and selenium(IV). Chloride in hot non-oxidizing acid medium will reduce Se(VI) to Se(IV) but not further. Sulphur dioxide will reduce Se(IV) to Se, but has no effect on Se(VI). Hydrazinium salts reduce both Se(VI) and Se(VI) to Se, but hydroxylammonium salts reduce only Se(IV) to Se. Hydrogen peroxide partially reduces Se(VI) to Se(IV) but not further. If chloride is also present [to reduce Se(VI) to Se(IV)], sulphur dioxide or hydroxylammonium salts can then reduce the Se(IV) to Se, and this combined effect has led to some confusion in interpretation of experimental observations. | 18,963,515 |
Determination by hplc of trifluoroacetate levels in plasma and urine of patients anaesthetized with halothane. | A new method is described for determination of trifluoroacetic acid (TFA) in biological fluids. Optimum extraction is achieved by addition of 18-crown-6 ether and acidification of the sample. The 4-bromomethyl-7-methoxycoumarin derivatives of the carboxylic acid are prepared and a sample is subjected to HPLC. A linear analytical curve of peak area against TFA concentrations ranging between 0.2 and 20 mug ml is obtained, and the minimum detectable concentration is estimated to be 0.1 mug ml . | 18,963,555 |
Ion-pair extractions with 12-crown-4 and its analogues. | The complexing abilities of 12-crown-4 and its analogues have been investigated by using ion-pair extractions. A relationship exists between the type of substitution on the 12-crown-4 and the complexing ability and selectivity. Additionally, the selectivities vary according to the reagent concentrations. The compound 12-crown-4 can be used to complex sodium selectively in the presence of other alkali-metal ions. A method for determining serum sodium-ion concentrations has been developed. | 18,963,560 |
Study of high-voltage breakdown and material consumption in spark-source mass spectrometry and their significance in analytical applications. | The breakdown voltage has been found to be dependent on the gap width between the electrodes and on the melting point of the sample elements in spark-source mass-spectrometry (SSMS). The number of discharges per pulse train and the time required to reach the first discharge depend only on the chosen breakdown voltage. The spark gap is proportional to the "radius" of the volume sampled (for a given element) and this radius is linearly related to the reciprocal of the melting point of the elements (23 different elements, metals or semiconductors), when fixed spark-parameters are used. The effect of electrode temperature on material consumption can be qualitatively explained by a fictive increase or decrease in melting point of the element. Knowledge of the relations between the different spark and instrumental parameters and the volume or weight of sample consumed can be applied to the study of the homogeneity of samples, to in-depth analysis by SSMS and to the analysis of microsamples. | 18,963,563 |
Investigation of the use of thermometric titrimetry for the determination of acidic substances in wine. | The use of thermometric titrimetry in the determination of acidic substances in red wine is described. The titration curve obtained in the thermometric titration of red wine with strong base presents two inflections. The stoichiometry corresponding to the first inflection presents good agreement with the so-called "total acidity" of wine, and is proposed for its determination. The second inflection is related to the content of phenolic substances in red wine. | 18,963,573 |
Binary data acquisition from instrumentation with BCD-coded output: a hardware converter and an example of the relative software control. | Simple hardware for conversion from BCD into binary code is described. The device is of low cost, performs a 16-bit conversion in a maximum time of 400 nsec, and is able to output the converted number to either an 8-bit or a 16-bit data bus. An example of the software necessary to perform data acquisition from a digital voltmeter by using this converter is also presented. | 18,963,586 |
Application of the deford and hume method modified for quasi-reversible and irreversible processes to the chelates of Bi(III) with azomethine derivatives of 2-benzoylpyridine. | The polarographic behaviour of the bismuth complexes of the oxime, hydrazone and thiosemicarbazone of 2-benzoylpyridine has been studied by differential pulse polarography. The DeFord and Hume method, modified for use with quasi-reversible and irreversible processes, has been applied for the calculation of the formation constants of these chelates, which exhibit different degrees of reversibility in their electroreduction. | 18,963,615 |
Background-current subtraction in voltammetric detection for flow-injection analysis. | A new approach for background-current subtraction for flow-injection systems using potential-scanning voltammetric detection is described. The method is based on recording voltamperograms while the sample and carrier solutions flow through the cell, and taking the difference as the net response for the sample. Background currents due to hydrogen evolution, oxygen reduction, solvent oxidation or surface processes are thus compensated, and detection limits at submicromolar levels can be obtained. The compensation for oxygen reduction current means that samples do not need to be deaerated. The method has been evaluated for reproducibility, concentration dependence, detection limit, etc. A flow-cell with a stationary disk electrode, a 200-mul sample volume, and rapid differential pulse scanning are used. At a flow-rate of 0.3 ml min about 15 samples can be assayed per hour. Chlorpromazine, phenol, acetaminophen, norepinephrine, lead, cadmium, bismuth and zinc were used as test species. | 18,963,616 |
Extraction of catechol violet, chrome azurol S and eriochrome cyanine R with chloroform solutions of liquid anion-exchangers. | The extraction of Catechol Violet, Chrome Azurol S and Eriochrome Cyanine R with chloroform solutions of tri-n-octylamine (TOA), TOA hydrochloride and Aliquat 336 has been investigated. From the extraction isotherms, absorption spectra of the organic phases and dependence of the extraction coefficients on extractant concentration, it was found that the singly-charged anions HL(-) are extracted preferentially, but acidic groups other than sulphonate can also form ion-pairs with alkylammonium cations at higher pH values of the aqueous phase, and at high acidity these dyes can be extracted other than by an anion-exchange reaction. The three dyes (especially Eriochrome Cyanine R and Chrome Azurol S) were strongly extracted with the liquid anion-exchanger used and Aliquat 336 was a better extractant than TOA or TOA hydrochloride. The absorption spectra for the organic phases containing Chrome Azurol S and Eriochrome Cyanine R depended on the extractant used. | 18,963,620 |
Exchange equilibria between bicarbonate, carbonate, chloride and bromide on dowex 1 x 8. | The exchange reaction 2R(+)HCO(3)(2-) + CO(3)(2-) right harpoon over left harpoon R(2)(+) CO(3)(2-) + 2HCO(3)(2-) has been studied on Dowex 1 x 8 in the presence of bicarbonate solution in equilibrium with atmospheric carbon dioxide (open system). The experiments showed, as theory predicts, that the composition of the resin phase is independent of the concentration of the bicarbonate solution. The mole fraction of carbonate at equilibrium is about 0.4 and the equilibrium constant is 0.15M at 20 degrees . With this value of the constant, the composition of the ion-exchanger for various bicarbonate concentrations has been calculated for a closed system. At [HCO(3)(-)] < 0.01M a substantial part of the resin is in the carbonate form, whereas for [HCO(3)(-)] 0.05M the resin is present almost exclusively in bicarbonate form. The exchange constants of bromide at trace level have been determined for the bicarbonate and mixed carbonate forms of the ion-exchanger. The exchange constant K(Cl)(HCO(3)) has been determined over the whole composition range and the results can be represented by K(Cl)(HCO(3))= 0.428 -0.063x(Cl) -0.115x(Cl)(2), where X(Cl) is the mole fraction of chloride in the resin. The constants are used to discuss the conditions for the Chromatographie enrichment of bromide from fresh water. | 18,963,640 |
Spectrophotometric studies on ion-pair extraction equilibria of the iron(ii) and iron(III) complexes with 4-(2-pyridylazo)resorcinol. | The ion-pair extraction equilibria of the iron(II) and iron(III) chelates of 4-(2-pyridylazo)resorcinol (PAR, H(2)L) are described. The anionic chelates were extracted into chloroform with benzyldimethyltetradecylammonium chloride (QC1) as counter-ion. The extraction constants were estimated to be K(ex1)(Fe(II)) = [Q{Fe(II)(HL)L}](0)/[Q(+)][{Fe(II)(HL)L}(-)] = 10(8.59 +/- 0.11), K(ex2)(Fe(II)) = [Q(2){Fe(II)L(2)}](o)/ [Q(+)](2)[{Fe(II)L(2)}(2-)] = 10(12.17 +/- 0.10) and K(ex1)(Fe(III)) = [Q{Fe((III))L(2)}](o)/(Q(+)][{Fe(III)L(2)}(-)] = 10(6.78 +/- 0.15) at I = 0.10 and 20 degrees , where [ ](o) is concentration in the chloroform phase. Aggregation of Q{Fe(III)L(2)} in chloroform was observed and the dimerization constant (K(d) = [Q(2){Fe(III)L(2)}(2)](o)/[Q{Fe(III)L(2)}](o)(2)) was evaluated as log K(d) = 4.3 +/- 0.3 at 20 degrees . The neutral chelates of {Fe(II)(HL)(2)} and {Fe(III)(HL)L}, and the ion-pair of the cationic chelate, {Fe(III)(HL)(2)}ClO(4), were also extracted into chloroform or nitrobenzene. The relationship between the forms and extraction properties of the iron(II) and iron(III) PAR chelates are discussed in connection with those of the nickel(II) and cobalt(III) complexes. Correlation between the extraction equilibrium data and the elution behaviour of some PAR chelates in ion-pair reversed-phase partition chromatography is also discussed. | 18,963,641 |
Extraction of potassium p-nitrophenoxide with macrocyclic crown ethers and cryptands from aqueous medium into diverse organic solvents: a systematic evaluation. | A systematic study has been made of the extraction of potassium p-nitrophenoxide from aqueous medium into a number of organic solvents that are immiscible or partly miscible with water, in the presence of several macrocyclic crown ether and cryptand complexing agents. The efficiency of extraction varies extremely widely with the nature of the ligand and the solvent. For some solvent systems, DC-18-C-6 is more efficient than [2.2.2] cryptand as an extradant. The extraction values, however, provide only limited insight into the fundamental reasons behind the observed results. Hence equilibria involved have been considered and the results analysed in terms of the equilibrium constants. The microscopic and macroscopic properties of these systems are discussed. | 18,963,655 |
Studies on extraction of indium by tributyl phosphate from thiocyanate solutions. | Indium can be quantitatively separated from a large number of elements which are usually associated with it, by extraction with 15% tributyl phosphate solution in kerosene from hydrochloric acid (pH 1)/0.5M potassium thiocyanate medium and stripping with 6M nitric acid. The equilibration takes 20 min. | 18,963,666 |
Determination of poly(oxyethylene) non-ionic surfactants by two-phase titration. | The solvent extraction of non-ionic surfactants with sodium hydroxide and tetraphenylborate has been studied, and a method developed for the determination of non-ionic surfactants by two-phase titration. A hydrophobic indicator system was used. The method is valid only when the concentration of anionic surfactant in the sample solution is lower than 1 x 10(-4)M. | 18,963,667 |
Use of ammonium molybdate in the colorimetric assay of cephalosporins. | A colorimetric method for the determination of five cephalosporins (cefoxitin sodium, cefotaxime sodium, cephapirin sodium, cephalothin sodium and cephaloridine), based on the blue colour formed by reaction of the cephalosporins with ammonium molybdate, is described. The effects of reagent concentration and reaction conditions are discussed. The proposed method has been applied to the analysis of cephalosporin injections, the results of which are in good agreement with those obtained by the official method of the British Pharmacopoeia. | 18,963,668 |
Stable-isotope ratio analysis based on atomic hyperfine structure and optogalvanic spectroscopy. | Atomic hyperfine structures were measured for the Cu I transition at 5782 A by optogalvanic spectroscopy at high resolution, with a cw dye laser. Samples were electro-deposited on the demountable cathode of a home-made hollow-cathode lamp. By spectral deconvolution, the relative isotopic abundances of (63)Cu and (65)Cu could be determined with good accuracy and precision. The technique is applicable to copper concentrations as low as 1.6 ppm. | 18,963,676 |
Influence of volatile hydride-forming elements on antimony determination by atomic-absorption spectrometry with hydride-generation. | A study was undertaken to determine the interfering effects of arsenic, bismuth, germanium, lead, selenium, tin and tellurium on trace determination of antimony by atomic-absorption spectrometry with hydride-generation. A 1% NaBH(4) solution was used as reductant and a small amount of oxygen was added to the hydrogen produced, to support the combustion and atomization of SbH(3). The interference from selenium in the determination of antimony is removed if potassium iodide-ascorbic acid solution or copper sulphate is added to the sample solution. The interference of tin and tellurium can also be avoided by adding potassium iodide-ascorbic acid solution. A possible interference mechanism is discussed. | 18,963,683 |
Determination of micro amounts of uranium by a molybdenum blue method. | A new and highly sensitive spectrophotometric method has been developed for the determination of micro amounts of uranium by a molybdenum blue method. The method is based on the observation that at low acidities uranium(IV) reduces ammonium molybdate to molybdenum blue, the absorbance of which is proportional to the amount of uranium present. The variables affecting development of the colour have been investigated and the conditions optimized. Beer's law is found to hold good for uranium concentrations between 1 and 20 ppm, with a precision of 2%. The effect of diverse ions has been studied. The method is useful for the determination of uranium present as an impurity (down to 0.1%) in plutonium, neptunium or thorium. | 18,963,698 |
Determination of cerium in silicate rocks by electrothermal atomization in a furnace lined with tantalum foil Application to 19 international geological reference materials. | A 40-fold increase in sensitivity obtained by using a tantalum foil lining in a pyrolytically-coated graphite furnace permitted determination of low ppm levels of cerium in most silicate rocks. A preliminary preconcentration by oxalate and hydroxide co-precipitations was used before determination by use of a Varian GTA-95 atomizer coupled with an AA-475 spectrometer. The results for 3 synthetic and 19 international reference materials, including 4 new Canadian iron-formation reference materials, showed good recovery and satisfactory agreement with other published values. | 18,963,724 |
Zinc and nickel ferrocyanides: preparation, composition and structure. | A review is given of work on nickel and zinc ferrocyanides during the period 1922-1983 with an emphasis on their compositions and structures in relation to the methods of preparation. | 18,963,739 |
Alkali-metal ion complexation with lariat ethers possessing a chromogenic group. | The extraction and complexation abilities of chromogenic alkyl crown-ether reagents were compared with those of their chromogenic benzo crown ether analogues. Improvements in the extraction efficiency and stability of the complexes were observed, and can be attributed to various factors such as increased lipophilic character and decreased charge separation. The spectral separation caused by the deprotonation of the amine-group was significantly decreased, so the usefulness of these compounds will be limited, until improved spectral separation can be achieved. | 18,963,740 |
Dissolution of geological material with orthophosphoric acid for major-element determination by flame atomic-absorption spectroscopy and inductively-coupled plasma atomic-emission spectroscopy. | An analytical procedure has been developed for the determination of major elements in geological material by both flame atomic-absorption spectrometry and inductively-coupled plasma atomic-emission spectrometry. Condensed phosphoric acid was used for the decomposition of 70 natural minerals containing sulphide, oxide, silicate or carbonate constituents. The results were compared with those obtained when a perchloric acid and orthophosphoric acid mixture was used for the decomposition, to ensure dissolution of even the most acid-resistant minerals. The procedure can be applied to rocks, ores, soils, slags and refractory material as a means of rapid and complete dissolution for the analysis of even the most insoluble material. | 18,963,741 |
Spectrophotometric determination of zinc with phenylfluorone in the presence of hexadecylpyridinium bromide and pyridine. | Phenylfluorone reacts with zinc in the presence of hexadecylpyridinium bromide and pyridine to form a water-soluble red chelate. The absorption maximum of the chelate is at 585 nm and its absorbance is constant in the pH range 7.7-8.2. At this wavelength, Beer's law is obeyed up to 1.53 x 10(-5)M zinc. The sensitivity is very high and the molar absorptivity is 8.0 x 10(4) l.mole(-1).cm(-1). The chelate has been utilized in the determination of zinc at the microgram level. The ratio of zinc to phenylfluorone in the complex is 1:1. | 18,963,754 |
Determination of hormones by time-resolved fluoroimmunoassay. | Immunoassays based on europium labels and time-resolved fluorescence as the detection method, have been developed. The specific activity of the label is several orders of magnitude higher than that of radioactive labels. Consequently, the technique provides great potential, especially in the determination of analytes which require high sensitivity. Both competitive and immunometric assays which use labelled antibodies have been worked out. In competitive assays the antigen is immobilized on a solid phase with a protein carrier. The antigen in the standard or sample then competes with the labelled antibody in solution. Separation is done simply by washing the wells in the microtitre strip where the assays are performed. Model systems are described for the measurement of testosterone and cortisol. Immunometric assays of human thyrotropin (hTSH) and luteotropin (LH) were performed with monoclonal antibodies, by either a one-step (hTSH) or two-step (LH) incubation procedure. These assays, which exploit the specific activity of the label, give a very high sensitivity and good reproducibility. The standard curves are linear and the dynamic range is at least 1000-fold. Because of the properties of the europium label and the simple assay design, the immunoassays based on time-resolved fluorescence are expected to gain wide application both in research and in routine determinations. | 18,963,767 |
Immunoassays in aqueous two-phase systems. | Aqueous two-phase systems provide a novel and convenient method for separating bound from free fractions in a binding assay. The ease of automation of this type of procedure makes it particularly attractive for separations based on immobilized ligands or binders or on adsorbents. | 18,963,768 |
Perturbation of laboratory test results by analytical interferences and drug effects. | An account is given of ways in which drug treatment can influence the results of laboratory tests for certain species of clinical importance, and of methods of detecting such interferences or effects. | 18,963,771 |
Determination of the rare earths, yttrium and scandium in silicate rocks and four new geological reference materials by electrothermal atomization from graphite and tantalum surfaces. | An improved graphite furnace atomic-absorption method has been developed for the determination of Sc, Y and the rare-earth elements in silicate rocks and related materials. The method, which involves the separation of the lanthanides by ion-exchange followed by their determination by electrothermal atomization, with use of an automatic sampling device, is more rapid than a previous method based on separation by co-precipitation with calcium oxalate and hydrous ferric oxide followed by normal injection of the solution into the furnace. Greater sensitivity (~ 10-40-fold) for La, Ce, Pr, Gd, Tb and Lu is also achieved by using a tantalum foil-lined graphite furnace instead of a pyrolytically-coated furnace. Results obtained for five international reference rock samples, NIM-G, SCo-1, MAG-1, SDC-1 and BHVO-1, are compared with those obtained previously by the oxalate-hydrous oxide co-precipitation method and with other published values. Results are given for four new Canadian iron-formation reference materials, FeR-1 to FeR-4. | 18,963,773 |
Computer control of microprocessor-based instruments by keypad emulation. | A keypad emulation method for controlling microprocessor-based instruments by laboratory microcomputers is presented. It is applicable to instruments that use "polled" keypad arrays; the instrument can be controlled by the laboratory computer or operated independently by manual keypad entry. To illustrate the approach, a microprocessor-based HPLC solvent-delivery system was controlled by a laboratory microcomputer which synchronized and sequenced the entire HPLC experiment, including solvent delivery, valve control for column switching and back-flushing, data-acquisition, and dataprocessing. | 18,963,782 |
Characteristics of industrial di(alkylphenyl)dithiophosphoric acids. | Instrumental and classical methods have been used to characterize some industrial di(alkylphenyl)dithiophosphoric acids. The (31)P-NMR chemical shifts of di(nonylphenyl)dithiophosphoric acid and its derivatives are summarized. | 18,963,798 |
Occurrence of consistent nM levels of phosphate in doubly demineralized and demineralized-distilled water. | A double demineralization system and a demineralization-distillation system operated over several months consistently delivered water that was approximately 30 nM in phosphate, as determined by a molybdenum blue spectrophotometric method. Silicate and hydrolysed polyphosphate in the water, and contaminants in the analytical reagents, were eliminated as sources of error in the determination. Caution is suggested in preparing blanks and dilutions in analyses of samples of natural waters or plant nutrient solutions, when either of these types of purification system is used. | 18,963,799 |
Complexometric determination of citric acid with copper. | A method is presented in which citrate is determined by complexation with excess of copper(II), followed by back-titration with EDTA. Small amounts of citrate can be determined by this method in the presence of large amounts of most organic acids present in natural products. Interfering reductants are removed by treatment with permanganate, amino-acids with nitrous acid, and metal ions with a cation-exchange resin. The indicator used for end-point detection is Szechromotrope, 4,4'-sulphonyl-bis(azobenzene) dichromotropic acid. | 18,963,814 |
[Not Available]. | The basic computer program MICMAC has been developed to fit equilibrium constants to various types of experimental data with a microcomputer. The program uses the very efficient Gauss-Newton-Marquardt algorithm for non-linear least-squares multiparametric refinement. Highly interactive, convenient to use and of modular design, it allows for a rigorous weighting scheme, and it takes account of possible systematic errors. This program is useful for solving problems with several sets of experimental data. Some examples dealing with polarography, pH-metric titration and (13)C-NMR are given, illustrating the versatility of MICMAC. Comparison is made with some recently published programs. | 18,963,839 |
Sensitive flotation-spectrophotometric determination of gold, based on the gold(I)-iodide-methylene blue system. | The gold(I)-iodide-Methylene Blue (MB) system is suitable for flotation separation and spectrophotometric determination of gold. Under the optimum conditions [(MB(+))(AuI(2)(-))].3[(MB(+))(I(3)(-))] is formed, and floated with cyclohexane. The product is dissolved in methanol and its absorbance measured. The molar absorptivity is 3.4 x 10(5)1.mole(-1).cm(-1) at 655 nm. The proposed method is more than three times as sensitive as the Rhodamine B method. Pt, Pd, Ag and Hg interfere seriously, and Ir, Rh, Bi and Cd to a smaller extent. Preliminary separation of gold by precipitation with tellurium as a collector is recommended. The method has been applied to determination of gold traces (about 1 x 10(-4)%) in a copper sample. | 18,963,845 |
Determination of sulpha-drugs with ion-selective membrane electrodes--II. | Two liquid-membrane electrodes, one sensitive to Cu(2+) and the other to Ag(+), were used for the determination of various sulpha-drugs with pK(a) > or = 6 (as the sodium salts) by potentiometric titration with CuSO(4) and AgNO(3). The construction and basic characteristics of these two electrodes are discussed. | 18,963,846 |
Spectrophotometric determination of silicon in silicates by flow-injection analysis. | A flow-injection spectrophotometric method has been developed for the accurate, continuous determination of silicon in silicate rocks. A rock sample solution is prepared by fusion with a 1:1 mixture of lithium carbonate and boric acid and subsequent dissolution of the cake in 1 M hydrochloric acid. The preparation technique is the same as that used for the determination of total iron, aluminium, calcium, titanium, and phosphorus in silicate rocks by flow-injection spectrophotometry. Because of the marked polymerization of silicic acid in acid solution, silicic acid is depolymerized in alkaline medium after a simple cation-exchange column filtration of the rock sample solution and then determined by a static or an FIA spectrophotometric method. The FIA system consists of two channels which carry the carrier solution and molybdate reagent, and allows the colour reaction to proceed under controlled conditions. The FIA system permits high throughput of 70 samples per hour. The procedure has been applied to a variety of standard silicate rocks of the U.S. Geological Survey and the Geological Survey of Japan, and gave satisfactory agreement with the recommended values. | 18,963,859 |
Etude par spectroscopie raman du chlorhydrate de cocaine. | Raman spectra of cocaine hydrochloride in the polycrystalline state and in saturated aqueous solutions have been recorded at room temperature from 0 to 4000 cm(-1) and at 9 K from 0 to 200 cm(-1) (only for the polycrystalline state). They show that cocaine can be characterized by the following proposed assignments. For the tropane nucleus the frequencies 851 and 786 cm(-1) (piperidine) and 896, 870 cm(-1) (pyrrolidine); these frequencies are assigned to ring carbon stretching vibrations V(C-C) Bands for the ester functional groups can be observed at 1713 cm(-1) (v(CO)) and 1203 cm(-1) (v((C-O-O)). The benzene nucleus is also important in characterization of cocaine hydrochloride because of its bands at 616, 990, 1000, 1026 and 1596 cm(-1). Special reference is made first to the work in the low-frequency range at room temperature and 9 K and secondly to the polarization studies of saturated aqueous solutions in the range 700-1726 cm(-1). The results constitute a pool of analytical characteristics which can be used for toxicological investigations, and also show all the possibilities of Raman spectroscopy in this field. | 18,963,861 |
Contributions to the theory of catalytic titrations-II Precipitation and redox catalytic titrations. | Precipitation and redox catalytic titration curves, obtained by both volumetric and coulometric addition of the titrant, have been simulated, taking into account the equilibrium concentration of the catalyst during the titration. The influence of several factors on the shape of the simulated catalytic titration curves has been investigated and is discussed in detail. Simulations of the blank titrations have also been made. | 18,963,897 |
Geographic approaches to quantifying the risk environment: drug-related law enforcement and access to syringe exchange programmes. | The concept of the "risk environment"--defined as the "space ... [where] factors exogenous to the individual interact to increase the chances of HIV transmission"--draws together the disciplines of public health and geography. Researchers have increasingly turned to geographic methods to quantify dimensions of the risk environment that are both structural and spatial (e.g., local poverty rates). The scientific power of the intersection between public health and geography, however, has yet to be fully mined. In particular, research on the risk environment has rarely applied geographic methods to create neighbourhood-based measures of syringe exchange programmes (SEPs) or of drug-related law enforcement activities, despite the fact that these interventions are widely conceptualized as structural and spatial in nature and are two of the most well-established dimensions of the risk environment. To strengthen research on the risk environment, this paper presents a way of using geographic methods to create neighbourhood-based measures of (1) access to SEP sites and (2) exposure to drug-related arrests, and then applies these methods to one setting (New York City [NYC]). NYC-based results identified substantial cross-neighbourhood variation in SEP site access and in exposure to drug-related arrest rates (even within the subset of neighbourhoods nominally experiencing the same drug-related police strategy). These geographic measures--grounded as they are in conceptualizations of SEPs and drug-related law enforcement strategies--can help develop new arenas of inquiry regarding the impact of these two dimensions of the risk environment on injectors' health, including exploring whether and how neighbourhood-level access to SEP sites and exposure to drug-related arrests shape a range of outcomes among local injectors. | 18,963,907 |
The behaviour of two types of copper ion-selective electrodes in different copper(II)-ligand systems. | The behaviour of two types of solid-state homogeneous sensors for copper(II), one based on pressed pellets of ternary CuAgSe and the other on thin-layer electroplated Cu(2-x)Se, in 12 different copper(II)-ligand systems, has been thoroughly investigated. Both electrodes exhibit anomalous behaviour when the ligands are of complexone type, the effect of the complexones on the deviations increasing in the order IDA < NTA < EDTA approximately DTPA, and being practically the same for the two types of sensors, thus disproving a previous suggestion that the anomaly is due to the silver in the silver-containing sensors. The experimental data do not support the specific ligand-adsorption hypothesis either. The observed deviations are tentatively explained on the basis that, as suggested by the selectivity coefficients, both sensors act as primary copper(I) ion-selective electrodes rather than copper(II)-electrodes. Thus, at very low copper(II) concentrations, according to the extended Nikolskii equation, the [Cu(I)]/[Cu(II)] ratio at the electrode surface determines the electrode sensitivity towards Cu(II). The lower detection limit could be improved by pH-control and selective complexation of Cu(I). This hypothesis has been proved experimentally. If the copper(I) activity on the electrode surface is decreased, the anomaly observed for the Cu(II)-NTA system disappears and decreases considerably for the Cu(II)-EDTA and Cu(II)-DTPA systems. | 18,963,923 |
Use of methyliminodiacetic acid bound to cellulose for preconcentration and determination of trace-metal cations. | Methyliminodiacetic acid immobilized on a cellulose support can be conveniently utilized for trace-metal uptake. Capacities and uptake yields as a function of pH have been evaluated for Pb(II), Cu(II), Mg(II), Ca(II), Cd(II), Zn(II), Co(II), Ni(II) and Hg(II) and the results compared with those predicted from the stability constants for the same systems in homogeneous solution. The immobilization of the ligand increases its co-ordinating ability. The applicability to speciation studies is considered. | 18,963,927 |
Multiparametric curve fitting--VIII: The reliability of dissociation constants estimated by analysis of absorbance-pH curves. | The program SPOPT estimates stability constants beta(pqr) and molar absorptivities epsilon(pqr) of all light-absorbing species M(p)L(q)H(r) by analysis of the absorbance-concentration (or absorbance-pH) curve. The program DCMINUIT estimates dissociation constants and molar absorptivities of protonated species. Both programs have been tested and compared with DCLET and LETAGROP-SPEFO for analysis of the overlapping equilibria of a triprotic acid. Computer plots of the residual-square-sum function are used to test the conditioning of parameters. Two approaches are made to formulation of the mathematical model, and several optimization algorithms are tested to find a reliable minimization procedure. The accuracy of ill-conditioned parameters is shown to be dependent on the precision of the absorbance measurements. General rules for investigation of A -pH curves are recommended. | 18,963,929 |
N-chlorophthalimide as a new oxidant for direct titrations in aqueous acetic acid medium. | A stable new oxidimetric titrant, N-chlorophthalimide in anhydrous acetic acid, is proposed for direct titrations of a variety of simple and complex reductants such as As(III), Sb(III), Fe(II), ferrocyanide, iodide, ascorbic acid, hydroquinone, hydrazine, phenylhydrazine, benzhydrazide, isonicotinic acid hydrazide, semicarbazide, thiourea, aniline, phenol, oxine and its metal complexes, and anthranilic acid and its metal complexes. | 18,963,951 |
Analytical properties of 2-oximinodimedone dithiosemicarbazone. | The synthesis and analytical properties of 2-oximinodimedone dithiosemicarbazone are described. | 18,963,954 |
Separation of trans-1,2-cyclohexanediaminetetra-acetic acid chelates of bismuth(III), iron(III) and copper(II) by reversed-phase paired-ion chromatography. | Trans-1,2-cyclohexanediaminetetra-acetic acid (DCTA) chelates of bismuth(III), iron(III) and copper(II) have been separated by two techniques using reversed-phase paired-ion chromatography. In one, the chelates in aqueous solution were separated within 20 min on a 6.0 x 300 mm ERC-ODS column with 10(-2)M tetrabutylammonium ion (TBA(+)) in methanoi-water mixture (45:55 v v ) as eluent. In the other, the metal ions in aqueous solution were separated within 10 min by direct injection into an ERC-ODS column with 10(-2)M TBA(+)/10(-3)M DCTA in methanoi-water mixture (40:60 v v ) as eluent. | 18,963,960 |
Calculation of equilibrium constants from multiwavelength spectroscopic data-III Model-free analysis of spectrophotometric and ESR titrations. | Factor analysis of spectroscopic data is a well-known tool for the determination of the number of independent absorbing species in a series of mixtures. It has also been used for the reduction of the data-set in the calculation of equilibrium constants from multiwavelength data. The paper presents a new application of this powerful technique. In a completely model-free treatment, data from spectrophotometric or other spectroscopic titrations are subjected to repetitive abstract factor analysis. By starting with only the first two spectra, and introducing the additional measurements one by one, the number of significant eigenvalues is obtained as a function of the progressing titration. On repetition of the process from the opposite end and judicious combination of the results, the formation and dissociation of individual "species" can be obtained. After association of actual stoichiometries with these purely abstract "species" by chemical reasoning, it may be possible to arrive at a semiquantitative description and reasonable estimates for the equilibrium constants. This method is most successful for the detection of minor species which would go unnoticed in any visual inspection of spectrophotometric titration curves. | 18,963,968 |
Spectrofluorimetric assay of tetracycline and anhydrotetracycline in combination. | Spectrofluorimetric methods are described for the assay of tetracycline (TC) and anhydrotetracycline (ATC) in combination, without prior separation. The interference from ATC in the TC assay has been corrected for by forming the aluminium complexes of both drugs and measuring the difference in fluorescence at 475 and 418 nm, with excitation at 393 nm. Similarly, measurement of the fluorescence of the magnesium complexes at 525 and 470 nm (excitation at 440 nm) nullifies TC interference in the ATC assay. | 18,963,972 |
Minipol, a desk-computer program for refinement of protonation constants from differential-pulse polarographic data. | The program MINIPOL, designed to run on a desk-computer with 32 kbytes of memory, can calculate the optimum values of overall protonation constants and molar intensities of up to 8 species with composition H(XXX)L(rho), from differential-pulse polarographic data. | 18,963,974 |
Colorimetric determination of two fenamates in capsule dosage form. | The colorimetric determination of mefenamic acid and flufenamic acid with potassium ferricyanide in sodium hydroxide medium is described. The orange product is measured at 464 nm. The molar absorptivities are 1.9 x 10(3) and 2.9 x 10(3) 1.mole(-1).cm(-1) for mefenamic acid and flufenamic acid, respectively. The method has been applied successfully to the determination of these drugs in capsules. | 18,963,983 |
Effect of cyclodextrin cavity size on sensitization of room-temperature phosphorescence of biacetyl. | The triplet-triplet energy-transfer reactions of several polynuclear aromatic compounds are enhanced to different degrees in alpha -,beta and gamma-cyclodextrin (CD) media when biacetyl is used as the acceptor species. The phosphorescence intensity of biacetyl increases as the size of the CD cavity increases. The CD cavities have specific dimensions which place constraints on the number of donor and acceptor molecules that can be included in them. The larger the cavity, the better it is able to include the reactants and, apparently, position them to increase the rate of triplet-triplet energy transfer. Compounds such as chrysene and triphenylene, which are unresponsive as biacetyl sensitizers in alpha-CD and beta-CD, are excellent sensitizers of biacetyl in the larger gamma-CD. Typically, limits of detection of 1 x 10(-6), 5 x 10(-7) and 1 x 10(-7)M were found with alpha-CD, beta-CD and gamma-CD, respectively. | 18,963,988 |
Postural and gait performance in children with attention deficit/hyperactivity disorder. | Up to 50% of children and adolescents with attention deficit/hyperactivity disorder (ADHD) exhibit motor abnormalities including altered balance. Results from brain imaging studies indicate that these balance deficits could be of cerebellar origin as ADHD children may show atrophy in those regions of the cerebellum associated with gait and balance control. To address this question, this study investigated postural and gait abilities in ADHD children and compared their static and dynamic balance with children with known lesions in the cerebellum. Children diagnosed with ADHD according to DSM IV-TR diagnostic criteria were compared with children with chronic surgical cerebellar lesions and age-matched controls. A movement coordination test was used to assess differences in motor development. Postural and gait abilities were assessed using posturography, treadmill walking and a paced stepping task. Volumes of the cerebellum and the cerebrum were assessed on the basis of 3D magnetic resonance images (MRI). Children with cerebellar lesions showed significant performance decrements in all tasks compared with the controls, particularly in the movement coordination test and paced stepping task. During dynamic posturography ADHD-participants showed mild balance problems which correlated with findings in cerebellar children. ADHD children showed abnormalities in a backward walking task and minor abnormalities in the paced stepping test. They did not differ in treadmill walking from the controls. These findings support the notion that cerebellar dysfunction may contribute to the postural deficits seen in ADHD children. However, the observed abnormalities were minor. It needs to be examined whether balance problems become more pronounced in ADHD children exhibiting more prominent signs of clumsiness. | 18,963,991 |
Extraction of manganese(II), iron(II), cobalt(II), nickel(II), copper(II), zinc(II), and cadmium(II) into 1,2-dichloroethane with 4,7-diphenyl-1, 10-phenanthroline and perchlorate. | The extraction of the ion-association complexes formed by Mn(II), Fe(II), Co(II), Ni(II), Cu(II), Zn(II) and Cd(II)-4,7-diphenyl-1, 10-phenanthroline (BP) chelates and perchlorate ions into 1,2-dichloroethane has been investigated. Extraction equilibrium for Mn(II), Cu(II), Zn(II) and Cd(II) is reached within 1 hr, but equilibration for Fe(II), Co(II) and Ni(II) is very slow; the equilibration rate depends on the structure of the chelating agent, the nature of the organic solvent, and pH. In the extraction equilibrium of Co(II) the rate-determining step seems to be the complexation of hydrated Co(II) by BP in the aqueous phase. | 18,964,002 |
Liquid-liquid extraction of univalent class b metal ions by the thiacrown compound 4'-picrylaminobenzo-1,4,8,11-tetra-thiacyclopentadec-13-ene. | A new thiacrown compound in which the picrylamino group is introduced as the chromogenic group, 4'-picrylaminobenzo-l,4,8,11-tetrathiacyclopentadec-13-ene (4'-PicNHBz-TTCP), has been successfully synthesized and its characteristics as an extracting and spectrophotometric reagent have been examined. This compound (HL) forms ion-pair complexes (M(+)L(-)) with univalent class b metal ions (M(+)) such as silver and copper(I). The M(+)L(-) species can be extracted into 1,2-dichloroethane and spectrophotometrically determined. Not only class a and ab metals but also bivalent class b metals such as mercury(II) and palladium(II) are not extracted at all. As silver and copper(I) ions are effectively extracted at pH above 8.0, a suitable masking agent such as tartrate is used in order to prevent the formation of hydroxides of foreign metals, if necessary. | 18,964,006 |
Reactions of nitrogen bases with nickel chelates of di-o-tolylcarbazone and di-o-tolylthiocarbazone. | The behaviour of nickel di-o-tolylcarbazonate and nickel di-o-tolylthiocarbazonate with organic nitrogen bases has been examined with a view to better understanding of the effect of different donor atoms in adduct formation. The adducts formed vary remarkably in composition and stability, and there are some interesting steric effects. | 18,964,009 |
Iridium in sea-water. | Iridium in sea-water has been measured (after isolation from the saline matrix by reduction with magnesium) by neutron bombardment, radiochemical purification and high-resolution gamma-ray spectroscopy. The concentration obtained in a Pacific coastal water was 1.02 +/- 0.26 x 10(-14) g per g of sea-water. At such extremely low concentrations, seawater is an extremely unlikely source for anomalously high iridium concentrations measured in the Cretaceous-Tertiary boundary layer of deep-sea sediments. | 18,964,014 |
Humoral immunity to HIV-1: neutralisation and antibody effector functions. | Several features of HIV have frustrated efforts to develop a vaccine able to induce broadly neutralising antibodies. The enormous genetic diversity of HIV is a major factor, accompanied by the camouflaged nature of the envelope spike, upon which HIV depends for cellular entry and to which antibodies must bind to neutralise. The picture is further complicated by the presence of nonfunctional envelope glycoproteins on the surface of HIV that are immunogenic. Consequently, HIV attracts antibodies that do not directly neutralise the virus but still activate complement and engage Fc receptors, which can both enhance and inhibit infection. The various effects that anti-envelope antibodies have on HIV infection will be reviewed here. Further research is needed to determine if these in vitro-characterised activities have relevance in vivo, and if some of the undesirable effects of non-neutralising antibodies can be avoided or the beneficial effects harnessed. | 18,964,020 |
The (political) economics of antiretroviral treatment in developing countries. | Despite unprecedented international mobilisation to support universal provision of highly active antiretroviral therapy (HAART), national governments continue to play the key role in determining access to treatment. Whereas some AIDS-affected countries have performed as well as or better than expected given their level of development, institutional characteristics and demographic challenges (e.g. Thailand and Brazil), others (notably South Africa) have not. This article argues that the 'economics' of antiretroviral drug delivery is at heart a political-economy of access to treatment. It depends on commitment on the part of national governments to negotiate with pharmaceutical companies over patented antiretroviral drug prices, on their policy towards compulsory licensing, and on the approach they adopt to delivering HAART. Civil society has an important role to play in encouraging governments to become, and remain, committed to taking action to ensure sustainable and widespread access to HAART. | 18,964,022 |
Analytical applications of absorption spectroelectrochemistry at grazing incidence. | Analytical applications of spectroelectrochemistry are limited by the short path-length, in the absorbing medium, that can be produced with most light-beam/electrode configurations. This disadvantage is overcome for grazing incidence. A cell fitted with glassy-carbon electrodes and used in a conventional spectrophotometer is described and applied to model systems illustrating the use of (a) homogeneous redox reactions, (b) homogeneous redox reaction followed by chemical reaction and (c) electro-deposition followed by stripping into a reagent solution. This last technique is the spectroelectrochemical analogue of anodic-stripping voltammetry. | 18,964,032 |
Preconcentration of cobalt with N-(dithiocarboxy)sarcosine and amberlite xad-4 resin. | Cobalt reacts with N-(dithiocarboxy)sarcosine (DTCS) to form a 1:3 Co:DTCS complex which is so stable that after its formation no decomposition occurs even in 4M hydrochloric acid. The complex is sorbed on a column of Amberlite XAD-4 copolymer from an acidic solution and eluted with 10 ml of a 1:1:3 v v mixture of 1.0M ammonia solution (pH = 9), 0.1M EDTA and methanol. The absorbance of the eluted chelate is measured at 320 nm against water ( = 2.15 x 10(4) l.mole(-1).cm(-1)). The recovery of cobalt from 1 litre of tap-water or sea-water is quantitative. The effect of diverse ions can be eliminated by the addition of EDTA after chelation of the cobalt. The copper complex with DTCS is partly sorbed on the column because of its slow rate of decomposition by EDTA, but most of the copper chelate sorbed can be eluted with hydrochloric acid and any co-eluted with the cobalt chelate can be completely decomposed by heating the eluate. Cobalt enrichment factors of at least 100 are obtained, so the method is applicable to the determination of cobalt at the ng ml level. | 18,964,053 |
Simultaneous polarographic determination of cadmium and tellurium in electro-deposited cadmium telluride thin films. | A polarographic method has been developed for the simultaneous determination of cadmium and tellurium in thin-film cadmium telluride. The procedure involves dissolution of the film with concentrated nitric acid, which is subsequently removed by evaporation. The Cd(II) and Te(IV) waves are well separated at pH 10, but sufficient ammonia must be present to prevent the precipitation of cadmium hydroxide. | 18,964,062 |
Trace determination of yttrium and some heavy rare-earths by adsorptive stripping voltammetry. | The interfacial and redox behaviour of rare-earth chelates with Solochrome Violet RS are exploited for developing a sensitive adsorptive stripping procedure. Yttrium and heavy rare earths such as dysprosium, holmium and ytterbrium can thus be measured at ng ml levels and below, by controlled adsorptive accumulation of the metal chelate at the hanging mercury drop electrode, followed by voltammetric measurement of the surface species. With a 3-min preconcentration time, the detection limit ranges from 5 x 10(-10) to 1.4 x 10(-9)M. The relative standard deviation at the 7 ng ml level ranges from 4 to 7%. A separation method is required to differentiate between the individual rare-earth metals. | 18,964,091 |
A new method for the atomic-absorption determination of lead blended as lead alkyls in motor spirit. | The total lead present as tetraethyl-lead (TEL) and tetramethyl-lead (TML) in motor spirit is determined by atomic-absorption spectrometry after decomposition by extraction with a mixture of mercaptoacetic acid and nitrous acid in the presence of hydrochloric acid. | 18,964,099 |
Analytical investigations on cephalosporins--IV: application of Ellman's reagent. | The application of 5,5'-dithiobis(2-nitrobenzoic acid) (Ellman's reagent) for the determination of microgram quantities of various selected cephalosporins in aqueous solution is described. Cephalosporin derivatives (cephalothin sodium, cephacetrile sodium, cefamandole lithium and nafate, cefoperazone sodium and ceftizoxime sodium) have to be treated with 0.5N sodium hydroxide before determination with Ellman's reagent, which reacts with free thiol groups. An aliquot of the solution is reacted with Ellman's reagent in pH 7.2 phosphate buffer and the absorbance of the resulting yellow solution is measured at 410 nm. The method, which is simple and precise, has been applied to determination of those cephalosporins in formulations, the results being compared with those obtained by the Ni-hydroxylamine method. | 18,964,102 |
[Not Available]. | Knowing the values of the equilibrium constants corresponding to the reactions N(2)O(4) right harpoon over left harpoon 2NO(2) and N(2)O(4) right harpoon over left harpoon NO(+) + NO(3)(-) in sulpholane, we have undertaken the electrochemical study of N(2)O(4) by means of linear and cyclic voltammetry at the platinum electrode. The N(2)O(4) species undergoes one oxidation step N(2)O(4) right harpoon over left harpoon 2NO(2) right harpoon over left harpoon 2NO(2)(+) + 2e and two reduction steps NO(2) + N(2)O(4) + e(-)right harpoon over left harpoon N(2)O(3) + NO(3)(-) (1st wave), followed by 3N(2)O(4) + 2e(-) right harpoon over left harpoon 2N(2)O(3) + 2NO(3)(-), N(2)O(4) + e(-) right harpoon over left harpoon NO + NO(3)(-), 2N(2)O(3) + e(-) right harpoon over left harpoon 3NO + NO(3)(-) (2nd wave). The redox properties of N(2)O(4) are complicated by trace quantities of water because of the formation of the electroactive species N(2)O(3), HNO(3) and HNO(2) according to N(2)O(4) + H(2)O right harpoon over left harpoon HNO(2) + HNO(3) and N(2)O(4) + HNO(2) right harpoon over left harpoon N(2)O(3) + HNO(3). The standard potentials of the couples concerned have been evaluated and are discussed. sont discutés et évalués. | 18,964,108 |
Adsorption of metal ions on activated carbon from aqueous solutions at pH 1-13. | Adsorption of microgram amounts of 20 metal species on activated carbon powder from aqueous solutions of pH 1-13 was investigated. The species examined were Cs(I), Y(III), Ce(III), Ti(IV), Zr(IV), Cr(III), Cr(VI), Mn(II), Fe(III), Co(II), Ni(II), Ru(III), Cu(II), Ag(I), Zn(II), Cd(II), Al(III), Pb(II), Sb(III) and Bi(III). | 18,964,109 |
Behaviour of some dialkyl- and trialkyl-lead compounds in the hydride-generation procedure using a non-dispersive atomic-fluorescence detector. | The method of generating covalent hydrides by reduction with sodium tetrahydroborate was applied to aqueous solutions containing traces of R(3)Pb(+) and R(2)Pb(2+) compounds (R = methyl, ethyl). For each compound the effects of sample acidity, sodium tetrahydroborate and hydrogen peroxide concentrations, reaction-vessel and transfer-line materials, were measured and the experimental conditions defined for obtaining maximum sensitivity. Experimental evidence indicating the formation of organolead hydrides during the reduction step at room temperature was adduced. The reaction efficiency was found to be 90% for trimethyl-, triethyl- and diethyl-lead and 59% for dimethyl-lead. In the case of inorganic lead the efficiency was only 27%. Without an intermediate preconcentration step, the detection limits obtained for trimethyl-, triethyl-, dimethyl- and diethyl-lead (3 times the standard deviation) were 3-5 ng of lead per litre. A procedure for discriminating between R(3)Pb(+), R(2)Pb(2+) and Pb(2+) compounds is proposed. | 18,964,111 |
Multiparametric curve fitting-IX Simultaneous regression estimation of stoichiometry and stability constants of complexes. | A chemical model (i.e., the number of complexes, their stoichiometry and stability constants with molar absorptivities) in solution equilibria may be established by (i) the trial-and-error method in which stability constants are estimated for an assumed set of complexes in the mixture and a fitness test is used to resolve a choice of plausible models to find the true one; (ii) the simultaneous estimation of the stoichiometry and stability constants for species divided into "certain" species for which the parameters beta(pqr), (p, q, r) are known and held constant, and "uncertain" species with unknown parameters which are determined by regression analysis. The interdependence of stability constants and particular sets of stoichiometric indices requires that the computational strategy should be chosen carefully for each particular case. The benefits and limitations of both approaches are compared by means of examples of potentiometric titration data analysis by the POLET(84) program and of spectrophotometric data analysis by the SQUAD(84) program. A strategy for efficient computation is suggested. | 18,964,117 |
A new reagent for determining trace selenium by gas chromatography: 1,4-dibromo-2,3-diaminonaphthalene. | 1,4-Dibromo-2,3-diaminonaphthalene is proposed as a reagent for conversion of selenium into a piazselenol, for determination by gas chromatography. The limit of detection is 0.03 ng of selenium. | 18,964,118 |
Solvent extraction of zinc with 5,7-dichloro-2-methyl-8-hydroxyquinoline into chloroform. | The distribution equilibria of the zinc complex with 5,7-dichloro-2-methyl-8-hydroxyquinoline in the water-chloroform system have been studied at 25 degrees . The influence of pH, reagent and metal concentrations, and the presence of sodium perchlorate in the aqueous phase has been determined. From quantitative evaluation of the extraction equilibrium data, it has been deduced that the complex extracted is the simple 1:2 chelate, ZnR(2), although at ligand concentrations higher than 0.3M, the self-adduct complex seems to begin to form. The extraction constant of the ZnR(2) species, refined by means of the program Letagrop-Distribution, has the value log K(ex) = - 6.15 +/- 0.07. | 18,964,125 |
The influence of thiourea on the cation-exchange behaviour of various elements in dilute nitric and hydrochloric acids. | Cation-exchange distribution coefficients for 21 elements between the cation-exchange resin AG50W-X4 and dilute nitric and hydrochloric acid containing up to 2.0M concentration of thiourea are presented. The ion-exchange behaviour of the elements and some possible separations are discussed. Four multi-element elution curves are presented, demonstrating the separation of the combinations Ga(Ag, Cu)Zn(Cd, Pb, In, Sn[IV]), CoPbSbTe, ZnCdBiHg, and AgCdInAu. | 18,964,128 |
Fluorimetric determination of boron at microgram level. | The synthesis, characterization and application of 2-(2-hydroxybenzylidenimine)benzene-arsonic acid (HBBA) as a reagent for the fluorimetric determination of boron are described. This reagent reacts with boric acid in 85% w/w sulphuric acid medium to yield a fluorescent compound. The reagent is not fluorescent in those conditions. Heating at 90 degrees for 45 min is needed for the compound to be formed. The linear calibration range is 0.1-8 microg/ml in the solution measured. The detection limit of the method is 0.01 microg/ml. The method has been applied to determine boron in vegetal material. | 18,964,136 |
Extraction and spectrophotometric determination of titanium(IV) with alizarin and fluoride. | The characteristics of the mixed-ligand titanium(IV)-fluoride-alizarin complex, including the optimum conditions of formation and extraction into methyl isobutyl ketone, are described. A simple and sensitive procedure for spectrophotometric determination of titanium has been developed. At pH 9.5-10.3 titanium reacts with alizarin in the presence of fluoride to form a red-violet complex that is completely extractable into methyl isobutyl ketone, and has its absorption maximum at 513 nm. The molar absorptivity at 513 nm is 7.0 x 10(4)l.mole(-1).cm(-1). Beer's law is obeyed up to 22 mug of titanium in 30 ml of solution. The method has been used for the determination of titanium in an oxide mixture and aluminium alloy samples. | 18,964,146 |
Fluorometric determination of nitrite. | A sensitive, simple and rapid fluorometric procedure for the determination of nitrite is described. It is based on the reaction of nitrite with 2,3-diaminonaphthalene in acidic solution to form 1-[H]-naphthotriazole, a highly fluorescent compound in alkaline medium. The detection limit is approximately 0.5 ng ml in the test sample (1% relative fluorescence intensity). Application of the method to analysis of a milk sample was tested with aliquots spiked with known amounts of nitrite. | 18,964,160 |
Effect of temperature on the determination of aromatic nitro-compounds by coulometrically generated chromium(II). | The analytical utility of the reaction between aromatic nitro-compounds and electrogenerated chromium(II) can be extended to several previously undeterminable compounds by increasing the temperature of the reaction solution. For some substances the stoichiometry of the reduction is changed; for others the rate of reaction, along with precision and accuracy, is appreciably increased; in at least one instance the reaction becomes less satisfactory as an analytical method. Temperature is thus shown to be an important variable that may explain differences in previously reported stoichiometries. | 18,964,192 |
Trace zinc determination by synchronous derivative fluorimetry. | A sensitive and selective synchronous-scanning derivative spectrofluorimetric determination of zinc based on the formation of a fluorescent chelate with 2-furaldehyde 2-pyridylhydrazone (FAPH) is described, and its analytical performance compared with that of the ordinary fluorimetric method. The detection limits lie in the ng ml range and the coefficient of variation is below 2% in both cases. The methods have been applied to the trace determination of zinc in pig liver tissue and environmental fume samples. | 18,964,201 |
Electroanalytical determination of vinca alkaloids used in cancer chemotherapy. | A differential pulse polarographic method has been developed for determination of the antineoplastic agents vincristine and vinblastine at ng ml level, in biological fluids such as plasma and urine. The vincristine and vinblastine are extracted from urine with Amberlite XAD-2. Linear calibration plots are obtained for both over the concentration range 0.005-5 mug ml . The relative standard deviations found were 1.7% for analysis of the pure drugs, 7.3% for urine and 8.6% for plasma. | 18,964,202 |
Determination of trace amounts of the flotation collectors ethyl xanthate and diethyl dithiophosphate in aqueous solutions by cathodic stripping voltammetry. | A cathodic stripping method has been devised for determination of low concentrations of the flotation collectors ethyl xanthate, diethyl dixanthogen and diethyl dithiophosphate. The limit of detection for ethyl xanthate was 1 x 10(-8)M by the differential pulse technique and with deposition for 2 min at -0.1 V. Three peaks were observed, each increasing in different concentration ranges of ethyl xanthate. A reaction mechanism is proposed. The detection limit for diethyl dithiophosphate was 1 x 10(-7)M by the differential pulse technique and with deposition for 3 min at -0.1 V. The analytical method was applied to determine ethyl xanthate in a sulphide mineral flotation plant and the amount of adsorbed ethyl xanthate and diethyl dithiophosphate on Cu(2)S. It was found that the adsorbed ethyl xanthate forms nearly a monolayer on Cu(2)S and that the amount of adsorbed diethyl dithiophosphate corresponds approximately to 0.4 monolayer. | 18,964,204 |
Determination of traces of EDTA, EGTA and DCTA by adsorptive accumulation of their complexes with hg(ii) followed by cathodic stripping. | The strong adsorption of the Hg(II) complexes of EDTA, DCTA and EGTA on a hanging mercury-drop electrode has been utilized in two procedures for cathodic-stripping determination of these complexing agents in water. The first procedure allows the determination of the free ligands or the total amount of 'available' metal. The second, which requires addition of excess of Hg(II) to the solution, gives the total amount of the ligand. The detection limit is 1 x 10(-8)M in the final solution at pH 4-6. | 18,964,207 |
Spectrometric analysis of non-metals introduced from a graphite furnace into a microwave-induced plasma. | A low-power helium microwave-induced plasma, sustained in a cylindrical TM(010) cavity, has been used with sample introduction from a graphite furnace. An end-on optical configuration was employed to monitor both atomic and ionic emission from Cl, I, S and P. The operating parameters were optimized with respect to the nature of the plasma background response, the limits of detection, and the shapes and linearity ranges of the log-log analytical working curves. Possible applications were evaluated by determining iodine in milk and analysing a multi-component mixture of sulphur compounds. | 18,964,219 |
Studies on fluorescein-III The acid strengths of fluorescein as shown by potentiometric titration. | Potentiometric back-titration of yellow solid fluorescein (H(2)Fl) and of red solid fluorescein in alkali with acid yielded titration curves that were practically identical in shape and position. The end-points at pH 8.5, 5.40 and 3.3 corresponded, respectively, to titration of the excess of standard alkali, and the successive protonations Fl(2-) + H(+) = HFl(-) and HFl(-) + H(+) = H(2)Fl. The pH at the mid-point of the first protonation yielded a value of 6.36 for pK(HFl) (ionic strength 0.10). Because of precipitation of yellow fluorescein during the second protonation step, a value for pK(H(2)Fl) could not be obtained. The total concentration of fluorescein at the first appearance of the precipitate fell on the curve for the solubility of yellow fluorescein as a function of pH. The titrations and the pK values found for the three acid groups of protonated fluorescein (H(3)Fl(+)) have been interpreted on the basis that in water fluorescein exists in only one structural form the yellow zwitterion. Similar back-titrations of alkalinized solutions of yellow or red fluorescein in 50% aqueous ethanol showed that in this medium fluorescein is present in only one form, presumably the quinonoid structure, with much weaker apparent acid functions, pK'(1) = 6.38 and PK'(2) = 7.16 (ionic strength 0.10). | 18,964,223 |
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