title stringlengths 0 1.13k | abstract stringlengths 1 15.7k | PMID int64 22 36.5M |
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Synthesis and ion-exchange properties of thermally stable stannic selenite. | Stannic selenites have been synthesized under a variety of conditions. The most stable sample is prepared by mixing 0-0.5M solutions of stannic chloride and sodium selenite in the ratio of 1:1 at pH 1. It is a bifunctional amorphous material. A tentative structure has been proposed on the basis of chemical composition, pH titrations, infrared and thermogravimetric analyses. Its ion-exchange capacity is 0.75 and 0.73 meq g after drying at 50 degrees and 500 degrees respectively. Its analytical importance has been established by the following quantitative separations: Cu(2+) from Ni(2+), Co(2+), Fe(3+), Ga(3+) and In(3+), Fe(3+) from Pb(2+) and Sc(3+), and Sc(3+) from VO(2+). | 18,961,152 |
Determination of subnanogram amounts of chromium in different matrices by flameless atomic-absorption spectroscopy. | A carbon rod flameless atomizer is used for the determination of Cr in water, sea-water, sugar, glycine and blood. The reported analytical curves show that the quantitative determination of Cr in these matrices is feasible in the ppM-ppm range. The influence of the most common anionic and cationic interferents is reported. | 18,961,155 |
Behaviour of ferroin indicator in iron(ii)- dichromate titrations A Critical study. | A critical evaluation has been made of the optimum conditions for a successful direct and reverse titration of iron(II) with dichromate, with ferroin as indicator, taking into account the influence of acidity, the catalytic effect of iron(III) and the induction effect of the iron(II)-dichromate reaction on the indicator oxidation reaction. The difference in the behaviour of the indicator in the direct and reverse titrations is believed to be due to the presence of a slow : step in the indicator oxidation mechanism ; this is however surmounted in the reverse titration, making it possible to use the indicator even in a 2N sulphuric add medium for this titration. The higher potentials recorded in the reverse titration are believed to be due to the oxide film on the platinum metal electrode. While iron(III) seems to help lower the kinetic barrier of the slow step sufficiently in the indicator oxidation mechanism, the ferriin-ferroin system seems to help m a similar way toe establishment of a more positive potential of the Ct(VI)/Cr(III) system at the platinum electrode in me direct titration; this value explains the feasibility of the direct visual titration in 2N sulphuric acid, although the colour change at the end-point is slow for other reasons. | 18,961,159 |
Formation of hydrogen peroxide upon oxidation of oxalic acid in presence and absence of oxygen-II Oxygen as oxidant. | Hydrogen peroxide, m a mixture that is 0.1M in manganese(II) sulphate and sulphuric add and exposed to light from a tungsten lamp, decomposes slowly at room temperature in a nitrogen atmosphere. At 75 degrees the reaction is fairly rapid in the dark (about 20-25% in 4 hr) and about 60% faster in light. Presence of oxalic add has little effect on the rate of disappearance of peroxide, the overall reaction corresponding to H(2)C(2)O(4) + H(2)O(2) --> 2CO(2) + 2H(2)O. In the presence of oxygen [and manganese(II)] this reaction does not take place; instead, hydrogen peroxide is formed and oxalic add disappears in equimolar amounts. The extent of all reactions greatly increases with increasing concentration of manganese. Acrylonitrilc acts as a retarder. Conditions m the presence of mangancse(II) are described, under which oxalic add can be oxidized quantitatively by oxygen to carbon dioxide with formation of an amount of hydrogen peroxide equimolar to the oxalic add oxidized. Reaction mechanisms are proposed to account for the fact that in the absence of oxygen 1 mole of peroxide disappears and in the presence of oxygen 1 mote of peroxide is formed for each mole of oxalic add reacted. | 18,961,168 |
Spectrophotometric determination of dimethyl sulphoxide. | A spectrophotometric method for the determination of milligram quantities of dimethyl sulphoxide in aqueous solutions has been developed. The method is based on the medium effect on the visible absorption spectra of metal salt solutions. Out of several compounds investigated, iron(III) alum was chosen as most suitable for this purpose. Beer's law is obeyed for dimethyl sulphoride concentrations up to 20 mg ml at 410 nm. Dimethyl sulphone does not interfere and dimethyl sulphide can be tolerated in amounts up to 25 % of the sulphoxide present. Possible interferences caused by metal cations can be avoided by passing the sample through a cation-exchanger before adding the reagent. The molar absorptivity is 3 l.mole(-1).cm(-1) at 410 nm, and the average relative error +/- 0.5%. | 18,961,176 |
Radiochemical separation of zirconium and hafnium from other radionuclides. | Radiozirconium and radiohafnium may be separated from all other radionuclides except scandium and protactinium by precipitation with mandelic acid from 5-10 M hydrochloric acid, using commercial zirconyl chloride as carrier. Scandium and protactinium are removed by dissolving the precipitate in sodium carbonate, then adding barium nitrate to precipitate barium carbonate which acts as a scavenger. Zirconium mandelate is finally reprecipitated and the sample weighed and counted in this form. The method was checked by analysing commercial zirconyl chloride and standard rock samples for zirconium and hafnium by neutron-activation analysis. | 18,961,201 |
New tests for the detection of azide. | Two new, simple, reliable, and specific colour tests are described for the detection of azide. In one, the azide is heated with allyl isothiocyanate and water to form 1-allyl-2-tetrazoline-5-thione in solution; the latter gives a yellow precipitate on treatment with bismuth nitrate solution. Pyridine enhances the intensity of the colour. The allyl isothiocyanate can be produced in situ by treating allylamine with carbon disulphide, diethylamine and hydrogen peroxide. In the other test the azide is heated with carbon disulphide, water and acetone, resulting in the formation of 1,2,3,4-thiatriazoline-5-thione which gives a yellow precipitate with Cu(II) or Bi(III). Pyridine again enhances the colour. The method is applicable to 5-10 mg of soluble azides, but insoluble azides cannot be tested. CN(-), SCN(-), and other common anions do not interfere. Only S(-2) interferes by masking the colour (black CuS or Bi(2)S(3) is precipitated). NO(2)(-) in larger amounts interferes in the second test. | 18,961,203 |
Quantitative reflectometry-I Principles and scope. | The technique of quantitative reflectometry is critically investigated, the model being the quantitative determination of nickel in aqueous media. Direct reflectance measurements can be made on commercially available nickel test-strips which develop a pink or red colour in the presence of nickel ions. Relative precisions at the 10 and 50 ppm levels are 2.3-3.6%. | 18,961,217 |
Potentiometric determination of stepwise stability constants of vanadium, molybdenum and tungsten chelates formed with asparagine and glutamine. | The metal chelates of V(IV), Mo(VI) and W(VI) formed with asparagine and glutamine have been studied potentiometrically. Stepwise stability constants in O.1M sodium perchlorate at 25 degrees C are reported as follows. Asparagine chelates--log K(1)K(2) 14.50 and log K(3) 4.04 for V, log K(1) 8.06, log K(2) 7.29 and log K(3) 3.45 for Mo, and log K(1) 5.84, log K(2) 5.11 and log K(3) 3.30 for W. Glutamine chelates--log K(1)K(2) 14.45, and log K(3) 4.07 for V, log K(1) 7.90, log K(2) 6.93, and log K(3) 3.35 for Mo, and log K(1) 5.76, log K(2) 5.09 and log K(3) 3.20 for W. | 18,961,248 |
Spectrophotometric determination of strychnine and methylatropine by extraction with tetrabromophenolphthalein ethyl ester. | A new application of monoacidic dyes is reported for the determination of strychnine and methylatropine. The method is based on solvent extraction into 1,2-dichloroethane of the ion-pair or addition compound formed between tetrabromophenolphthalein ethyl ester and quaternary ammonium salts or alkaloids. The absorbance of the extracts is linearly dependent on the concentration of strychnine or methylatropine initially present in the aqueous solution. | 18,961,259 |
Study of Cu(II)-hydrazine-6-methylpicolinaldehyde system: A new "in situ" reaction. | The Cu(II)-hydrazine-6-methylpicolinaldehyde system in solution is studied. The "in situ" reactions, based on the formation of a ligand by condensation of an amine and an aldehyde in the presence of the metal ion, and the consequent formation of the coloured Cu(I)-azine and Cu(l)-hydrazone complexes are reported. A new mode of homogeneous colour development, based on the exchange of groups in the ligand with the metal ion present, is also described. The results are compared with those obtained with the previously synthesized reagents. | 18,961,260 |
A phosphorimetric investigation of the external heavy-atom effect in aqueous solution and its correlation with phosphorescence intensity and quantum yield. | Excitation and emission phosphorescence spectra, lifetimes, and relative quantum yields of benzene and ten monosubstituted benzenes were determined at 77 K in methanol/water 10/90 v/v and in sodium iodide/methanol/water solutions. Substituents CHO, COCH(3), COC(2)H(5), OH, OCH(3), H(3), C(2)H(5), CH(2)OH and N(CH(3))(2) were investigated. Aqueous sodium iodide solutions were found to be a suitable heavy-atom solvent for phosophorimetry. Heavy-atom enhancement factors ranged from 1.2 to 8.3 according to the molecular structure and a marked decrease of the lifetime was observed for nine compounds in aqueous sodium iodide solution. A linear log-log correlation was obtained between the relative corrected phosphorescence signal and the heavy-atom enhancement factor of the monosubstituted benzenes. A similar correlation was found between the quantum yields and the heavy-atom enhancement factors. The analytical usefulness of these correlations is evident for the prediction of the magnitude of the heavy-atom effect. | 18,961,273 |
Indirect polarographic determination of tripolyphosphate ions in the presence of other polyphosphates, with octyltin chloride. | Tripolyphosphate ions form a soluble complex with mono-octyltin cations, thus reducing the polarographic wave height ofthe octyltin. This provides a method for the determination of 2 x 10(-4)-4 x 10(-3)M tripolyphosphate in the presence of 2 x 10(-3)M ortho-, pyro-, trimeta-, and 10(-3)M tetrametaphosphate, together, or in any combination. The method is also insensitive to less than 2 x 10(-3)M magnesium or calcium and less than 10(-2)M sulphate. | 18,961,280 |
Application of indirect methods in analysis by atomic-absorption spectrometry. | The use of indirect methods for the determination by atomic-absorption spectrometry of those elements not normally amenable to sensitive determination by this technique is reviewed. The available indirect methods are classified into five general types of procedure; specific reported procedures for the determination of metals, non-metals and some compounds are discussed. | 18,961,303 |
Ultramicro atomic-absorption spectroscopy with a tungsten-filament atom-reservoir. | The detection and measurement of traces of zinc, lead, copper and silver by atomic-absorption spectroscopy, with a tungsten-filament atom-reservoir (TFAR), hollow-cathode lamps and limited-field viewing is described. The performance of this atom cell is compared with that of the carbon-filament atom-reservoir for determination of lead. Greater sensitivity and fewer matrix effects are observed with the TFAR system. The lifetime of the tungsten filament is almost indefinite. | 18,961,305 |
Acid-base equilibria in ethylene glycol--I: definition of pH and determination of pk-values of acid-base indicators. | A pH-scale in ethylene glycol is defined, based on potentiometric measurements for a cell without liquid junction: glass electrode || 0.1M (HCl + KCl), ethylene glycol | AgCl:Ag; and a potentiometric-spectrophotometric method for the determination of pK-value of acid-base indicators in ethylene glycol on the basis of this pH scale is proposed, in which the pH scale is established and the pK-value determined in a single titration at constant ionic strength. The following pK-values of indicators are reported: Cresol Red-3.00, Thymol Blue-3.39, Bromophenol Blue-6.49, Bromocresol Green-7.38, Bromocresol Purple- 9.00 and Cresol Red (2nd change)-11.07. A linear relationship was found between the pK-values of four sulphonphthalein indicators in ethylene glycol and in water according to the following equation (pK(HI)(c))(EG) = 2.3 + 1.1 (pK(HI)(c))(W). An attempt is made to explain this dependence, based on the idea of solute-solvent interaction of species of the same charge type. | 18,961,308 |
Oxidation with permanganate in presence of fluoride potentiometric determination of manganese(II). | The effects of acidity, fluoride concentration, temperature and concentration of manganese in the reaction between KMnO(4) and Mn(II) were studied potentiometrically. The rate of reaction is increased by increasing the fluoride concentration and/or decreasing the acidity of the solution. The formal redox potentials of the MnO(-)(4)/Mn(III) and the Mn(III)/Mn(II) systems were determined at different pH values. The E degrees values obtained by extrapolation to pH = 0 were 1.58 and 1.52 V respectively. The amount of Mn(II) determined was varied from 5 to 56 mg. The net reaction can be represented as MnO(-)(4) + 10HF(-)(2) + 4Mn(2+) right harpoon over left harpoon 5MnF(-)(4) + 2H(+) + 4H(2)O. | 18,961,313 |
Simultaneous determination of N-unsubstituted- and N-substituted nitroazoles and criteria for their identification-I Nitroimidazoles and nitropyrazoles-polarographic determination. | The N-unsubstituted nitroazoles have an imino hydrogen atom in contrast to the N-substituted derivatives, and react with hydroxide to give nitroazole anions. The strongly negative shift of E(1 2 ) for these anions makes possible simultaneous polarographic determination of any pair of compounds, one of which is an N-unsubstituted nitroazole and the other a corresponding N-substituted derivative. Simultaneous polarographic determination of three compounds [4(5)- 4- and 5-nitroimidazole] is also possible from alkaline medium, but only when DeltaE(1 2 ) between the N-substituted isomers is at least 100 mV. Chromatographically, and/or by some other criteria it is possible to distinguish between the N-unsubstituted nitroazole and the N-substituted derivatives. These compounds appear together in reaction mixtures arising during substitution of the hydrogen atom. | 18,961,314 |
Complexation of polyvinyl acetate with iodine. | Polyvinyl acetate and iodine form a characteristic red complex in the presence of potassium iodide. Spectrophotometry of the complex at 510 nm in a methanol-water system at 20 degrees yields linear calibration curves over the range 25-100 mg of polyvinyl acetate per 1. of final solution. The limit of detection is 0.1 mg of polyvinyl acetate in 0.5 ml of initial sample. Replacement of acetate groups by inert groups reduces the sensitivity of the method, and other details of the system are discussed. | 18,961,316 |
The performance characteristics of analytical methods-III. | The range of concentrations covered by an analytical method is an important performance-characteristic, and suggestions are made for definition of this range. The ability to detect small concentrations are also considered, and it is suggested that the standard deviation of blank determinations be quoted as the performance-characteristic relevant to the power of detection. | 18,961,338 |
Determination of Hg(II) in acidic media by stripping voltammetry with collection. | Stripping voltammetry with collection at a rotating ring-disk electrode having a platinum ring and a glassy-carbon disk was used for the determination of Hg(II) in 1.0M H(2)SO(4) medium in the range 0.10-4.00 ppM. Satisfactory results were obtained only after a thin film of Au (two monolayer equivalents) was electroplated on the disk electrode. The average relative deviation of the results for determination at the 0.10-ppM level was 7.5 %. The limit of detection for the technique is approximately 0.01 ppM. | 18,961,350 |
Aromatic sulphonate ion-selective electrode membrane with crystal violet as ion-exchange site. | Four triphenylmethane derivatives (cations) and a high molecular-weight quaternary ammonium ion were used as the ion-exchange site in the liquid membranes of electrodes responsive to aromatic sulphonate ions, such as benzenesulphonate and alpha-naphthalenesulphonate. The nitrobenzene or 1,2-dichloroethane membrane containing the Crystal Violet-aromatic sulphonate pair had good sensitivity, showing an approximately Nernstian response down to 10(-4)M sulphonate. The potential of the Crystal Violet membrane was independent of pH variation from 2.5 to 12. Chloride and sulphate ions in the aqueous sample solution did not affect the electrode potential. 1,3,6-Naphthalenetrisulphonate exerted essentially no influence on the potential of the alpha-naphthalenesulphonate electrode. The interference of the nitrate ion was relatively large. The conductivity and association of the solute species in the membrane were estimated. | 18,961,356 |
Determination of lithium stearate in sebacate-based lubricants by atomic absorption. | An accurate method is proposed for the determination of lithium stearate in sebacate-based lubricants. The sample is treated with dilute hydrochloric acid and an extraction is performed with ethyl ether to remove di-isopropyl phosphite which would otherwise interfere by causing the subsequent precipitation of lithium phosphate or lithium metaphosphate. The aqueous extract is then evaporated to fuming with perchloric acid and the lithium is determined by atomic absorption. | 18,961,363 |
NMR determination of the microscopic constants of diprotonated diamines in aqueous solution. | The microscopic acidity constants of the diprotonated asymmetric N-methyl-substituted ethylenediamines and N-methylpiperazine were determined by using the change of the chemical shift of the methyl protons with varying acidity. The determination was carried out at 25 degrees in aqueous solution and in an ionic medium of 1M KNO(3). The basicity of the amino-functions follows the expected sequence: secondary > primary 2 > tertiary. The influence of the substituent on the basicity of the end-group is primary > secondary 2 > tertiary. | 18,961,374 |
Interpretation of mass spectra. | A computer programme is described which calculates the mass numbers and the relative intensities of each of the lines in the cluster formed in a mass spectrometer from a single type of fragment ion which contains one or more polyisotopic elements. Many elements such as B, C, S, Cl and Br possess more than one naturally occurring isotope, and the relative abundances of the various isotopes are known. A whole series of possible fragment ions may be calculated quite readily, and the results, which are printed numerically and in the form of a histogram, facilitate the interpretation of mass spectra. Trial data, a FORTRAN listing of the programme, and a sample of the output are given. The programme requires approximately 17K of fast core, and should be implemented without difficulty on any computer with a FORTRAN IV compiler. | 18,961,381 |
Indirect flame-photometric determination of silicon. | An indirect flame-photometric method for the determination of silicon in terms of the potassium in precipitated K(2)SiF(6) has been developed. Optimum conditions have been found for the precipitation and the washing of the precipitate with aqueous ethanol. Satisfactory results have been obtained for silicon contents > 1 % in ores and alloys. | 18,961,383 |
Coulometric microdetermination of peroxides--I. Hydrogen peroxide. | An electroanalytical method, based on controlled-potential coulometry in the iodine-iodide system, has been developed for determination of small amounts of hydrogen peroxide. The sample is added to an electrolyte containing an acid solution of iodide and the iodine, which is produced rapidly, is reduced at a rotating platinum electrode. The number of coulombs consumed in the cell reaction is determined by electronic integration. Samples containing 1 microg-1 mg of hydrogen peroxide were analysed with an accuracy of +/-0.2%. The analysis time ranged from 3 to 7 min. | 18,961,387 |
Selective separation of uranium from other elements by cation-exchange chromatography in hydrobromic acid and hydrochloric acid-acetone mixtures. | U(VI) can be separated from Ga, Fe(III), Bi, Pb, Cd, Zn, Cu(II) and Au(III) by quantitative elution with 0.50M HBr in 86% acetone or with 0.35M HBr in 90% acetone from a column of AG50W-X4 cation-exchange resin of 200-400 mesh particle size. U(VI) and many other ions are retained. U(VI) then can be eluted selectively with 0.50M HCl in 83% acetone or with 0.35M HCl in 85% acetone. Co(II), Mn(II), Mg, Ca, Ti(IV), Al, Zr, Th and La are quantitatively retained by the column. These elements then can be eluted with 5M HNO(3). At the higher acid concentration (0.50M) the separation between U(VI) and Li is not satisfactory but is excellent at the lower acid concentration; the U(VI) peak is sharper at the higher acid concentration. Separations are sharp and quantitative, as is demonstrated by results for some synthetic mixtures. Distribution coefficients and elution curves are presented. | 18,961,390 |
Determination of vanadium and molybdenum by atomic-absorption spectrophotometry. | A method is described for the determination by atomic-absorption spectrophotometry of vanadium and molybdenum, up to the milligram level, in samples of yellow cake, uranium-bearing minerals and geochemical standards. After attack with acids these two elements are separated from each other and from matrix elements by means of anion-exchange in 6M hydrochloric acid on the strongly basic anion-exchange resin Dowex 1, X8 (chloride form). Vanadium is unadsorbed and passes into the effluent while molybdenum is adsorbed on the resin. For the elution of molybdenum a mixed aqueous-organic solvent system consisting of methanol and 6M hydrochloric acid (9: 1 v/v) is used. After evaporation of the 6M hydrochloric acid effluent and of the mixed aqueous-organic eluate vanadium and molybdenum are determined by atomic-absorption spectrophotometry. The method was tested by analysing numerous samples with contents ranging from a few ppm to milligram amounts of vanadium and molybdenum. For comparison, the concentrations of these two elements were determined in a large number of samples by spectrophotometric and titrimetric procedures. In all cases very good agreement of results was obtained. | 18,961,392 |
Solvent extraction-spectrophotometric determination of rare earths with chlorophosphonazo-III. | The rare-earth chlorophosphonazo III chelates are easily extracted from an aqueous solution (pH 1.1-1.5) into n-butanol. The absorbance at the absorption maximum (at 668 nm) is about 3 times that in aqueous solution. The spectrophotometric determination of rare earths has been investigated. | 18,961,422 |
Evaluation of 1-(2-thiazolylazo)-2-hydroxy-3-naphthoic acid as a metallochromic indicator. | The acid dissociation constants of 1-(2-thiazolylazo)-2-hydroxy-3-naphthoic acid (TAHN) and the formation constants of Cu(II), Ni(II) and Zn(II) chelates of this dye have been determined spectrophotometrically at 25 degrees in a 5% v/v mixture of dioxan and water. The formation constants of the 1:2 chelates are smaller than those of other o-hydroxythiazolylazo compound chelates. TAHN is a satisfactory indicator for the titrations of Cu(II) and Ni(II) with EDTA. | 18,961,425 |
Rapid EDTA determination of lead in binary alloys of lead and tin. | Binary alloys of lead and tin were dissolved in nitric acid (1 + 1) containing 10% sodium fluoride. The tin(IV) was effectively masked by the fluoride. The lead was quickly and accurately titrated with EDTA in a hexamine-buffered solution, with Xylenol Orange as indicator. | 18,961,427 |
Detection and spectrophotometric determination of cobalt with dimedone dioxime. | Dimedone dioxime forms coloured complexes only with cobalt, nickel and copper ions in alkaline solution. Acidification and solvent extraction enables cobalt (1-50 mug) to be determined spectrophotometrically without interference. A specific spot test for cobalt is based on the same reaction. | 18,961,442 |
The error in absorption measurements caused by the use of non-monochromatic light-III Application to linear calibration curves. | When in spectrophotometry the absorption is measured with non-monochromatic light, a curved calibration curve is often obtained. Some errors are introduced if a linear calibration curve is still used. The magnitude of these errors has been calculated. | 18,961,446 |
Stepwise a.c. amperometric titration of cadmium and zinc with EGTA. | The theory of d.c. and a.c. amperometric titrations based on complexometric reactions is presented. It is shown that when E(1 2 )(M(I)) > E(1 2 )(M(II)) and log K(M(I)L) < log K(M(II)L), M(I) and M(II) can be sequentially determined by d.c. as well as a.c. amperometric titration. If, on the other hand E(1 2 )(M(I)) > E(1 2 )(M(II)) and log K(M(II)L), a stepwise titration can be performed only by a.c. amperometry. The effect of oxygen on an a.c. amperometric titration is also discussed. The stepwise a.c. amperometric titration of cadmium and zinc with EGTA at pH 6 in the presence of oxygen and an excess of 0.05 M acetate illustrates the theory. | 18,961,447 |
Rapid determination of the equivalence volume in potentiometric acid-base titrations to a preset pH-II Standardizing a solution of a strong base, graphic location of equivalence volume, determination of stability constants of acids and titration of a mixture of two weak acids. | A newly proposed method of titrating weak acids with strong bases is applied to standardize a solution of a strong base, to graphic determination of equivalence volume of acetic acid with an error of 0.2%, to calculate the stability constants of hydroxylammonium ion, boric acid and hydrogen ascorbate ion and to analyse a mixture of acetic acid and ammonium ion with an error of 0.2-0.7%. | 18,961,474 |
Applications of enzyme-catalysed reactions in trace analysis-VII Determination of lead and indium by their inhibition of isocitrate dehydrogenase. | The inhibition of isocitrate dehydrogenase by lead, indium and calcium has been studied. Methods for the determination of 0.024-1 mug of lead and indium, based on this inhibition, are outlined. Lead may be separeted from some interfering ions by extraction with tributyl phosphate in isobutyl methyl ketone, before application of the enzymic reaction. | 18,961,476 |
Comparison between amperometric and true potentiometric end-point detection in the determination of water by the Karl Fischer method. | A rapid and sensitive method using true potentiometric end-point detection has been developed and compared with the conventional amperometric method for Karl Fischer determination of water. The effect of the sulphur dioxide concentration on the shape of the titration curve is shown. By using kinetic data it was possible to calculate the course of titrations and make comparisons with those found experimentally. The results prove that the main reaction is the slow step, both in the amperometric and the potentiometric method. Results obtained in the standardization of the Karl Fischer reagent showed that the potentiometric method, including titration to a preselected potential, gave a standard deviation of 0.001(1) mg of water per ml, the amperometric method using extrapolation 0.002(4) mg of water per ml and the amperometric titration to a pre-selected diffusion current 0.004(7) mg of water per ml. Theories and results dealing with dilution effects are presented. The time of analysis was 1-1.5 min for the potentiometric and 4-5 min for the amperometric method using extrapolation. | 18,961,491 |
Katalytische bestimmung von silberspuren in wabetariger lösung und nach extraktion. | The application of the catalysed oxidation of Bromopyrogallol Red by potassium per- sulphate for silver determination is discussed. In aqueous solution silver concentrations of 0.5- 1 mug/ml can be determined and 1- 13 ng/ml in the presence of 1, 10-phenanthroline as activator. In combination with solvent extraction, catalytic determination of the extracted silver is possible even in presence of 200 mug of iron(III), cobalt(II) and palladium(II). By means of an automatic variant of the simultaneous comparison method a more sensitive determination (0.2-20 ng/ml) was achieved. | 18,961,494 |
Phase-titration analysis of ternary mixtures containing mutually miscible components. | A method, based on phase-titration, for the analysis of ternary mixtures composed of mutually miscible components is described. One of the components is determined by an independent chemical or physical means and its concentration in the original mixture then brought to a fixed value by adding a calculated amount of one of the three components. The resultant mixture is then titrated to the turbidimetric end-point with a titrant which is immiscible with one of the components and the composition of the sample is computed from a calibration curve. The method is illustrated by its application to benzene-methanol-acetic acid and benzene-toluene-acetic acid mixtures. | 18,961,497 |
Polystyrene impregnated with beta-diphenylglyoxime, a selective reagent for palladium. | alpha- and beta-diphenylglyoximes impregnated on macroreticular polystyrene (XAD-2) were tested as adsorptive reagents and one of them (the beta-isomer) was found to adsorb palladium in preference to platinum (selectivity factor 20) and nickel (factor > 100). | 18,961,503 |
Preparation, properties and analytical application of thorium n-phenyl-o-nitrobenzohydroxamate. | A new complex of thorium(IV) with N-phenyl-o-nitrobenzohydroxamic acid (PNHA) has been prepared by reacting an aqueous solution of thorium with an alcoholic solution of PNHA at 60 degrees C and adjusting the pH to 4-4.5. The infrared spectra and thermal analysis of the complex are discussed. The use of PNHA for gravimetric determination of thorium is described. | 18,961,504 |
[Not Available]. | The method for the determination of sulphur in organic compounds (E. Debal and R. Levy, Bull. Soc. Chim. France, 1968, 426; 1971, 3374) by combustion in oxygen at 1310-1320 degrees C and coulometric titration of the sulphur dioxide formed is improved. Silver and 8-hydroxy-quinoline are successfully used to remove halogens (fluorine included) from combustion products. A new glass cell for the acidimetric titration of sulphur dioxide with an automatic coulometer is devised, with a water-jacket for its cathodic and reference compartments. The constant-temperature water-flow makes this determination easy to carry out with no drawbacks, even in varying ambient temperature. | 18,961,505 |
Spectrophotometric determination of iron in sea-water by solvent extraction as the ternary complex iron(II)-2-nitroso-4-chlorophenol-rhodamine B. | Iron has been determined in sea-water by extraction of the ternary complex of iron(II) with 2-nitroso-4-chlorophenol and Rhodamine B at pH 4.7 and measurement at 558 nm. Toluene is used as the organic solvent. Any iron(III) is reduced with hydroxylammonium chloride. | 18,961,509 |
Complexation reactions of pyridinols. | Complexation of iron(III) with several pyridinols has been studied and used in selective detection and determination (spectrophotometric and chelatometric) of the metal. Iron(III)-pyridinol complexes are also used as indicators in acid-base titrations. A thiol group vicinal to a phenol group in a pyridine molecule provides a reagent that is a suitable ligand for palladium(II) determination. Stability constants of bivalent metal complexes with pyridinols have been determined potentiometrically. | 18,961,528 |
Thiomercurimetric determination of sulphur, aliphatic and aromatic thiols and disulphides in hydrocarbon solvents, using reduction with sodium aluminium bis(2-methoxyethoxy)dihydride. | A method is proposed for determination of hydrogen sulphide and aliphatic and aromatic thiols in hydrocarbon solvents by extraction with 2M potassium hydroxide and titration with o-hydroxymercuribenzoic acid in the presence of dithiofluorescein and dithizone, with selective masking with acrylonitrile. Sulphur and organic disulphides are readily converted by sodium aluminium bis(2-methoxyethoxy)dihydride in benzene solution into hydrogen sulphide and thiols, which can either be directly titrated after dilution with alcohol or separated by extraction and determined in the presence of each other. | 18,961,530 |
Redox indicator properties of some substituted chrysoidins. | Indicator properties of eleven substituted chrysoidins have been studied. Conditional reduction potentials of the three appreciably reversible indicators in this group were obtained by classical approaches and by use of a potentiopoised standard solution procedure. Chemical and electrochemical observations lead to the conclusion that the other eight indicators act irreversibly in their oxidation. Hence, only transition potential ranges can be reported for these. Substitution in other than the 4-position induces greater irreversibility, while the hydroxy group in the 4-position produces a greater degree of reversibility than does either the methoxy or ethoxy group, 4-Hydroxychrysoidin appears to be the best of the group for bromate titrations. | 18,961,544 |
Study of ion-association complexes used in spectrophotometric determination of iron. | The following ion-association systems were investigated spectrophotometrically: Fe(2,2'-bipyridyl)(3)(Methyl Orange)(2); Fe(1,10-phenanthroline)(3)(Methyl Orange)(2); Fe(4,7-diphenyl-1,10-phenanthroline)(3)(Methyl Orange)2; Fe(1,10-phenanthroline)(3)(Benzyl Orange)2; Fe(4,7-diphenyl-1,10-phenanthroline)(3)(Benzyl Orange)(2). The molar absorptivities may be calculated with good precision on the basis of the spectra of the reacting species (iron chelate and dye anion), their stoichiometry and the degree of extraction. Analytically the most useful is the Fe(1,10-phenanthroline)(3)(Methyl Orange)(2) complex, molar absorptivity 4.83 x 10(4) 1. mole(-1) cm(-1) at 420 nm, but many metals (Co, Cu, Ni, Zn, Cd) form similar extractable complexes and interfere. | 18,961,549 |
Atomic-emission spectrometry with an induction-coupled high-frequency plasma source Comparison with the inert-gas shielded premixed nitrous oxide-acetylene flame for multi-element analysis. | The performance for trace analysis in solution by atomic-emission spectrometry from a 36-MHz induction-coupled radiofrequency plasma atom-cell is predicted from a simple model and compared with the corresponding characteristics of an inert-gas shielded nitrous oxide-acetylene flame. A longer linear calibration range is predicted for the plasma source owing to the greater freedom from self-absorption under optimum operating conditions, and the long residence time of analyte species confers freedom from solute vaporization interferences. The predictions are verified experimentally and the advantages of the use of the plasma source are demonstrated in the analysis of aluminium alloys for copper, iron, magnesium, manganese, titanium and zinc. | 18,961,578 |
On the reduction of oxygen in aqueous solution by electrolytically precipitated cadmium. | The reduction of oxygen in aqueous solution by electrolytically precipitated cadmium, used in a reductor column, has been studied in two ways. First, by analysis of the effluent for the hydrogen peroxide formed as a reaction intermediate, the conditions for quantitative reduction have been found. Attention is called to the fact that an effluent free from hydrogen peroxide also implies quantitative reduction of all dissolved oxygen. The practical consequences are pointed out. A comparison is also made with some other reductors. Secondly, the oxidation of electrolytically precipitated cadmium by hydrogen ion is strongly inhibited, so at pH 7 it is possible to determine oxygen as the equivalent amount of cadmium ion produced in the reductor column. The conditions of quantitative reduction of oxygen are determined and found to be in agreement with those obtained by the first method. From the results the solubility of oxygen in water in equilibrium with air is estimated and found to agree with a published result considered as reliable. An outline is given of a method for determination of oxygen in aqueous solution by measurement of the amount of cadmium ions produced. | 18,961,595 |
Comparison of an instrumental and modified Kjeldahl technique for determination of nitrogen in niobium and tantalum alloys. | Results obtained for the determination of nitrogen in two tantalum alloys and six niobium alloys by modified Kjeldahl and Leco TC-30 nitrogen-oxygen determinator are compared. In the 5-25 ppm range, for tantalum alloys, the relative standard deviation was 3-9% by the Kjeldahl procedure and 9-11% by the instrumental technique. In the range 30-80 ppm, for niobium alloys, the relative standard deviation was 2-8% by the Kjeldahl procedure and 5-7% by the instrumental technique. | 18,961,607 |
Controlled potential lodometric determination of nitrate after reduction to nitrite by coppered cadmium. | A controlled-potential coulometric iodometric method previously developed for the accurate determination of small amounts of nitrite has been extended for the determination of nitrate after its reduction on a coppered cadmium reductor. The conditions for quantitative reduction have been investigated with respect to type of reductor and pH. Nitrate-nitrogen in the range 0.01-100 mug ml may be determined with high accuracy in less than 10 min, including the reduction step. The method has been applied with good results to a large variety of samples such as meat products, juices and waste waters. | 18,961,612 |
Gravimetric determination of selenium from perchloric acid solution with hydrazine. | The gravimetric determination of selenium, by reduction of selenious acid in perchloric acid solution with hydrazine hydrate, has been studied in detail. Elemental selenium is completely precipitated in 3.2-5.1M perchloric acid at room temperature or 100 degrees C. One mole of selenious acid reacts with one mole of hydrazine hydrate to give elemental selenium. | 18,961,615 |
New redox titrants in non-aqueous or partially aqueous media-V Potentiometric titrations with iodosobenzene diacetate in acetic acid medium. | A stable new redox titrant, viz., iodosobenzene diacetate in anhydrous acetic acid medium, is proposed for the potentiometric determination of a number of reductants such as As(III), I(-), Fe(II), N(2)H(4), [Fe(CN)(6)](4-), Tl(I), Sb(III), hydroquinone, ascorbic acid, phenol, aniline and oxine. | 18,961,616 |
The use of 5-(4-pyridyl)nonane for the separation of chromium(vi) from fission products in hydrochloric acid media. | The distribution of chromium(VI) between 5-(4-pyridyl)nonane in benzene and hydrochloric acid media has been studied as a function of the concentration of the acid, extractant, chromium(VI), chloride and a few other ions. The extraction mechanism and the composition of the extracted complexes of Cr(VI) have been proposed. The separation of Cr(VI) from uranium, thorium and fission products in 3M hydrochloric acid has been achieved. | 18,961,632 |
A study of some pyridylazo dyestuffs as chromogenic reagents and the elucidation of the nature of their metal complex spectra. | A series of dyestuffs having the same basic structure as 2-(2-pyridylazo)-5-diethyl-aminophenol (PADAP) but varying in their substituents on the 5-positions of both rings has been prepared. Dissociation constants for three such dialkylaminophenol derivatives have been determined, the pK(OH) values being of the same order as that reported for 4-(2-pyridylazo)resorcinol (PAR), while the pK(NH) values are lower. Two different 5-bromo-PADAP complexes are formed with the uranyl ion, one between pH 2 and 5 which is a neutral complex and probably a dimer, and the other an unstable neutral complex which forms between pH 5.5 and 8 and is a 1:1:1 ternary hydroxo-complex. A stable 1:1:1 ternary fluoro-complex is also formed between pH and 6 and 8. Double maxima occur in the spectra of all the metal complexes of these dyes. Evidence given shows the double peaks to originate from the one moiety and to be directly related to the presence of a substituent on the benzene ring para to the azo linkage. A tautomeric equilibrium with two imine tautomers in addition to the azo form of the complex is postulated and it is suggested that they correspond to the three composite bands given by computer analysis of the spectrum. | 18,961,644 |
Direct photometric titration of tellurium. | A direct photometric titration method has been developed for the determination of tellurium. Tellurium(IV) is titrated with potassium dichromate in 2-6M nitric acid (or 1-4M perchloric acid) at 380-430 nm (blue-violet filter). Selenium(IV) does not interfere. | 18,961,646 |
Advantages of statistical design in the investigation of titrimetric methods, as exemplified by a factorial-experiment study of the ferric iron-ascorbic acid titration system. | An example is outlined of the application of factorial experiment-design to the development of a titrimetric method, and the usefulness of such designs to analytical chemistry is discussed. | 18,961,652 |
A stable d.c. capillary arc plasma for solution analysis. | The analytical capability of a d.c. capillary arc plasma, operating on argon, is described. Solutions containing Cd, Pb, Hg, I, As and Zn are introduced into the plasma from a tantalum-filament atomizer. Signals are observed from both the arc and the tail-flame. The problem of sample rejection by the hot plasma is illustrated and discussed. | 18,961,653 |
Acid-base equilibria in ethylene glycol--II: autoprotolysis constants and acid-base properties of ethylene glycol and its mixtures. | The acid-base behaviour of ethylene glycol and its mixtures with water (1, 5 and 10%), methanol, ethanol, isopropanol, nitromethane (each 10%) and ethyl methyl ketone-chloroform (5 + 5%) have been investigated by potentiometric titration, in a cell without liquid junction, equipped with a glass and a silver-silver chloride electrode. The autoprotolysis as well the protolysis constants of phthalic acid were determined for each mixture. The added solvents improve the properties of ethylene glycol, decreasing the viscosity without changing the acid-base behaviour of the ethylene glycol itself, which is favourable for the titration of weak bases. Water increases the basic, and nitromethane the acidic, properties of the mixture. Small quantities of water (ca. 1%) do not impair the titration conditions. | 18,961,676 |
Polarographic reduction of methylene blue in presence of clay minerals. | Clay-Methylene Blue suspensions have been examined polarographically. The degree of binding of the dye on the clay particles has been calculated. The possibility of using the data in estimating the clay content of a sample and identifying the mineral is suggested. | 18,961,669 |
Colour changes of chemical indicators-VI: metallochromic indicators for direct chelometric titrations of zinc. | Eriochrome Blue SE, Eriochrome Red B, Naphthylazoxine 6S, SNAZOXS, and Zincon have been studied in order to find optimum conditions for their use as metallochromic indicators in direct visual chelometric titrations of zinc. The sharpness of the indicator transitions has been investigated by means of photometric titrations and the colour quality has been specified with the aid of the C.I.E. chromaticity systems. Zincon and Eriochrome Blue SE have been found to be the most convenient for visual titrations of zinc. | 18,961,678 |
Spectrographic determination of impurities in ultrapure tungsten and tungsten oxide. | The effects of an external magnetic field and of the diameter of the anode on the spectroscopic line intensity of the impurity elements in ultrapure tungsten and tungsten oxide have been studied. The results obtained are used for the development of a more sensitive method for the determination of these impurities (Mn, Pb, Fe, Ni, Al, Mo, V, Cu, Cr). | 18,961,672 |
3-methyl-2-oxazolidone as a solvent for acid-base titrations. | 3-Methyl-2-oxazolidone has been evaluated as a solvent for the titration of various weak carboxylic acids and phenols. Its high dielectric constant and wide liquid range contribute to its outstanding solvent properties. Tetrabutylammonium hydroxide was the titrant. End-points were determined potentiometrically with a glass-calomel electrode system. FORTRAN computer programs were used to evaluate the results, and relative acid strengths were determined and related to the aqueous acidity. The accuracies obtained are comparable to those for other solvent media. An 800-mV potential span is available in this solvent, which may allow differentiating titrations to be performed. No titrations of acid mixtures were attempted, but it was found possible to distinguish both neutralization steps for salicylic acid and o-phthalic acid. | 18,961,698 |
The analysis of detergents. | A review is made of the analysis of detergents, covering the determination of all classes of component materials. | 18,961,702 |
Atomic-absorption determination of manganese, cobalt and copper in whole blood and serum, with a graphite atomizer. | A new and rapid method is described for the determination of Mn, Co and Cu by atomic absorption with a graphite atomizer and deuterium compensation, on very small samples of whole blood and serum, with no preliminary manipulations. The metal concentrations in blood serum from healthy donors have been found to be Mn 9 +/- 4.3 ng ml ; Co 7.7 +/- 1.9 ng ml and Cu 1.2 +/- 0.16 mug ml . | 18,961,710 |
The use of long-chain alkylamines for preconcentration of traces of molybdenum, tungsten and rhenium in their determination by atomic-absorption spectroscopy-I General studies. | Long-chain alkylamines are used for the preconcentration of traces of molybdenum, tungsten and rhenium as thiocyanate complexes, in their determination by atomic-absorption spectroscopy. General studies of factors, influencing the extraction show that the thiocyanate complexes can be extracted into chloroform containing a low concentration of Amberlite LA1. Detection limits are 0.02 ppm Mo, 0.75 ppm W and 0.34 ppm Re in the final MIBK solution and are improved by a factor of 5-10 over those obtained by using current extraction methods. Serious interelement effects are eliminated and a range of other cations and anions are shown to have little effect on the absorption. | 18,961,721 |
Basicity of nitropyrazoles and their simultaneous spectrophotometric determination. | The protonation constants of some 1-, 3(5)-, 3-, 4- and 5-nitropyrazoles have been determined, and compared with those of nitroimidazoles. The effect of the position of the nitro group in the pyrazole and imidazole ring is discussed. The ortho effects of the nitro group in pyrazole and imidazole are compared and found to have identical values. The effect of the nitro group on protonation constants is greater when the nitro group is close to the pyridine nitrogen atom. This, together with the ability of N-unsubstituted nitropyrazoles to dissociate to give nitropyrazole anions, with an accompanying shift of the spectra to longer wavelengths, permits the simultaneous spectrophotometric determination of nitropyrazoles. | 18,961,738 |
Spectrophotometric determination of tungsten in ores and steel by chloroform extraction of the tungsten-thiocyanate-diantipyrylmethane complex. | A method for determining up to about 6% of tungsten in ores and mill products is described. It is based on the extraction of the yellow tungsten(V)-thiocyanate-diantipyrylmethane ion-association complex into chloroform from a 2.4M sulphuric acid-7.8M hydrochloric acid medium containing ammonium hydrogen fluoride as masking agent for niobium. The molar absorptivity of the complex is 1510 1. mole(-1).mm(-1) at 404 nm, the wavelength of maximum absorption. Moderate amounts of molybdenum and selenium may be present in the sample solution without causing appreciable error in the result. Interference from large amounts is avoided by separating these elements from tungsten by chloroform extraction of their xanthate complexes. Large amounts of copper interfere during the extraction of tungsten because of the precipitation of cuprous thiocyanate. Common ions, including uranium, vanadium, cobalt, titanium, arsenic and tellurium, do not interfere. The proposed method is also applicable to steel. | 18,961,741 |
Spectrophotofluorometric determination of some alkaloids containing a tertiary amine group. | The method developed involves the base-catalysed condensation of mixed anhydrides of organic acids, where a tertiary amine group functions as the basic catalyst. The product of the condensation reaction is highly fluorescent and allows the fluorometric determination of alkaloids containing a tertiary amine group, in the ng ml range. The mixed anhydride system is simple to prepare and the fluorogenic reaction is completed within 15 min at 80 degrees . The reaction is specific for, but does not distinguish between, different tertiary amines. | 18,961,745 |
An evaluation of solvent mediators for ion-selective electrode membranes based on calcium bis(dialkylphosphate) sensors trapped in poly(vinyl chloride) matrices. | This study on several alkan-1-ols, di-n-octylphenyl phosphorate and di-n-nonyl phthalate as solvent materials in ion-selective electrode membranes based on calcium bis(dialkylphosphate) sensors trapped in a PVC matrix indicates that the best electrodes are made with di-n-octylphenyl phosphonate. These are selective for calcium. The liquid alcohols readily exude from the PVC matrix, and solid alcohols are completely unsuitable for membrane fabrication. However, despite a tendency to be exuded, decan-1-ol gives acceptable electrodes responsive to bivalent cations if calcium bis (di-2-ethylhexylphosphate) is used as sensor. Several selectivity coefficients, k(caj), greater than unity were found, but though such values for j = Na or K do not involve complete loss of selectivity towards calcium, a value of K(CaCu) = 13 for a membrane with di-n-nonyl phthalate as mediator and calcium bis(di-n-decylphosphate) as sensor indicates greater selectivity for copper than for calcium. | 18,961,752 |
Utilization of an Hg(2+)-sensitive membrane-electrode in the complexometric determination of Bi(3+), Fe(3+) and Cr(3+). | The paper reports the results obtained in the complexometric determination of Bi(3+), Fe(3+) and Cr(3+) by using an Hg(2+)-sensitive membrane-electrode for the end-point indication. The determination of Bi(3+) and Fe(3+) is performed after addition of mercuric complexonate from which these cations release Hg(2+) by means of which the electrode senses the equivalence point. In the case of Cr(3+) an excess of complexone is added and the surplus is titrated with a standard solution of Hg(2+) in the presence of the Hg(2+)-sensitive membrane-electrode. | 18,961,754 |
Chromatography of aromatic compounds on anion-exchange resins. | Complex mixtures of aromatic compounds can be rapidly separated on anion-exchangers in the acetate form with acetic acid as eluent and determined automatically by recording the absorbance in the ultraviolet. Carboxylates are separated by ion-exchange. Hydrogen bonds between non-disso-ciated acids and the counter-ions influence the distribution coefficients. Hydrogen-bonding with the resin has a marked effect on the sorption of solutes containing phenolic protons. Intramolecular hydrogen-bonding depresses their sorption. Hydrophobic interactions have a predominant influence with hydrocarbons and with phenolic compounds containing non-polar aliphatic substituents. The relative importance of these interactions increases with a decreased ion-exchange capacity of the resin. | 18,961,772 |
Sequential determination of thorium and rare earths with EDTA and kojic acid. | Kojic acid can be used instead of acetylacetone to form a ternary complex with Th-EDTA that is more stable than the corresponding Xylenol Orange ternary complex, thus making it possible to titrate lanthanides with EDTA at pH 5.5 after titration of thorium at pH 2. | 18,961,798 |
Trace characterization of powders by atomic-absorption spectrometry: the state of the art. | A review is made of the progress achieved in the last 15 years in the field of trace characterization of powders by direct atomic-absorption spectrometry. The studies covered include the development of novel atomization devices, modification of existing atomic-absorption spectrometers, and the use of closed-cavity vaporizers. A description is given of the capsule-in-flame and circular-cavity furnace type atomizers designed on this principle, of the procedure employed in powder-sample analysis and of some analytical features of the methods used. In conclusion, various modern analytical methods are compared as to the possibilities they offer for the determination of ultratraces in solids, and suggestions are made concerning the possible role of atomic-absorption spectrometry. | 18,961,816 |
Studies on synthetic inorganic ion exchangers-V: preparation, properties and ion-exchange behaviour of amorphous and crystalline thorium tungstate. | Amorphous and crystalline thorium tungstate have been prepared by mixing 0.1M thorium nitrate and 0.1M sodium tungstate under different conditions. The physico-chemical properties, chemical stability, composition, TGA, DTA, X-ray, infrared absorption and ion-exchange behaviour of thorium-tungstate are reported and discussed. Distribution coefficients of metal ions on thorium tungstate have been determined at pH 2-3 and 5.5-6.5. Selective ion-exchange separations of bismuth and mercury from other metal ions have been achieved on a column of thorium tungstate. | 18,961,820 |
Miniature potassium-sensitive electrodes with neutral carriers in a poly(vinyl chloride) matrix. | A miniature version of the potassium ion-selective electrode with valinomycin or dimethyldibenzo-30-crown-10 in a poly(vinyl chloride) matrix is described. Electrodes having an effective membrane area of <0.2 mm(2) exhibit Nernstian behaviour within a range of activities of the potassium ion of 10(-1)-10(-5)M, a rapid response and good long-term potential stability. | 18,961,826 |
An evaluation of four titrimetric methods for the determination of lead in ores. | Four titrimetric methods for the determination of lead in ores were evaluated. In the absence of bismuth and indium, a method based on EDTA titration of lead, after chloroform extraction of lead diethyldithiocarbamate, yields accurate and more precise results than the other methods evaluated. Interference from indium can be avoided by di-isopropyl ether extraction of its bromide from 6M hydrobromic acid. Interference from bismuth can be eliminated by separating it from lead by chloroform extraction of its xanthate from 2M hydrochloric acid-tartaric acid media. | 18,961,829 |
Trace analysis for chlorinated hydrocarbons in air by quantitative combustion and coulometric chloride determination: application to standardization of vinyl chloride permeation tubes. | Methods for high-temperature combustion of vinyl chloride in air were studied theoretically and two types of gas mixtures were found to give 100% conversion into HCl. The chloride was determined by coulometric titration with silver, in 70% acetic acid. Good agreement between theoretical and experimental results was obtained. Permeation rates of vinyl chloride from fluorinated ethylene propylene permeation tubes were determined gravimetrically and with the coulometric method developed. The standard deviations of the methods were 0.002 and 0.001 microg min respectively for permeation rates of 0.5 microg min when the temperature was controlled to +/- 0.02 degrees . The coulometric mean value was 99.9% of the gravimetric mean; 1 ppm of vinyl chloride in air could be determined coulometrically with a standard deviation of about 0.002 ppm. | 18,961,836 |
Relative sensitivity coefficients for the analysis of steel by spark-source mass-spectrometry. | Quantitative analysis by spark-source mass-spectrometry requires the knowledge of socalled sensitivity coefficients for the elements being determined. Five series of analyses have been carried out on five different steel standard reference materials (NBS-SRM 661-665), using photoplate detection. The relative sensitivity coefficients (S(R)) of Ti, V, Cr, Mn, Co, Ni, Cu, As, Zr, Nb, Mo, Sn, Sb, La, Ta and W were determined vs. iron as an internal standard. The S(R) values were independent of the elemental concentration. A relative standard deviation of about 15% was obtained. The accuracy as confirmed by comparing the results for a pure iron sample with those obtained by neutron-activation analysis was within the same limits. | 18,961,876 |
On the copper(II)-EDTA-par system for visual and photometric end-point detection in iron(III)-EDTA titrations. | The copper(II)-EDTA-PAR system is proposed as indicator for direct EDTA titration of 0.2-20 mg of iron(III) in acetic acid medium. The precision and accuracy have been evaluated by spectrophotometric titration. Microtitrations determine down to 10 mug of iron. A logarithmic concentration diagram has been constructed to present the complex equilibria involved. In an interference study the masking agent ammonium fluoride was found to improve the end-point detection. The method has been applied successfully to practical standard samples and compares favourably with other EDTA titrations of iron. | 18,961,892 |
Metal oxide electrodes as sensors in complexometric titrations. | EDTA titrations of lead and manganese, and of some other ions by using these as indicator ions, have been followed potentiometrically with PbO(2) and MnO(2) electrodes. Explanations are put forward for the anomalies observed in the titration curves. With the MnO(2) electrode, formation of an Mn(III)-EDTA complex is responsible for the diminished potential breaks. With the PbO(2) electrode the decrease in the potential break and the distortion of the curves in acid solution may be due to reaction between electrode coating and titrant. The MnO(2) electrode has been used for titrations of Ba(2+) Ca(2+), Cd(2+) and Cu(2+) with errors < 1%. | 18,961,911 |
Semimicro determination of mercaptans with copper(II). | A rapid and precise titrimetric method for the determination of mercaptans on the semimicro scale is described. Samples dissolved in water, methanol. dimethylformamide or acetonitrile are treated with a measured excess of cupric sulphate. After 1 min, the excess of copper(II) is back-titrated with standard mercaptoacetic acid solution. At the end-point the violet complex first formed changes to a permanent yellow. The method is applicable to a variety of mercaptans and accurate to 0.2%. It is relatively free from interferences. | 18,961,968 |
Accuracy of analysis of steels by use of a spark-source mass spectrometer with electrical detection. | The precision and accuracy of spark-source mass spectrometry with electrical detection has been studied, with five steel standard reference materials (NBS-SRM 661-665). Two different modes of analysis have been evaluated, magnetic scanning with electrical detection of the individual ions in sequence, using the total ion-current as reference, and magnetic switching between masses, with current integration. Measurements of isotope abundances have been used to evaluate the precision. The relative sensitivity coefficients of Ti, V, Cr, Mn, Co, Ni, Cu, As, Zr, Nb, Mo, Sb, La, Ta and W have been determined vs. iron as an internal standard. The accuracy of analyses based on these experimentally measured relative sensitivity coefficients was confirmed by comparing the results for a pure iron sample with those obtained by neutron-activation analysis. | 18,961,984 |
Ion-exchange separation and atomic-absorption determination of fifteen major, minor and trace elements in silicates. | A scheme of ion-exchange separation of fifteen elements (major, minor and trace) determined mainly by atomic-absorption spectrophotometry (Ti by colorimetry) is applied to rock, mineral and ceramic analysis. Mn, Cu, Co, Fe and Zn are separated on an anion-exchanger and Li, Na, K, Mg, Ca, Sr, Ti, Al, Ni and Ba on a cation-exchanger. The method has been tested by analysis of a synthetic mixture of the fifteen ions in the ratios in common rock samples, and of various international standards (100-mg samples). | 18,962,010 |
Acid-base titrations by stepwise addition of equal volumes of titrant with special reference to automatic titrations-IV Photometric titration of an acid. | In Part I of this series, evaluation methods for potentiometric titrations of acids performed by stepwise addition of titrant were introduced. These methods are non-approximative and may therefore in principle be applied to titrations of acids of any strength. This paper demonstrates that photometric titrations performed by stepwise addition of titrant may also be evaluated by the proposed methods. The photometric method is compared with the potentiometric method of monitoring the course of a titration. | 18,962,034 |
Differential pulse polarography of some benzodiazepines and their determination in urine. | A differential pulse polarographic method has been applied to the determination of diazepam, oxazepam, nitrazepam and flurazepam down to 2 x 10(-7)M (0.14 mug/ml). The method can also be used with biological materials such as urine, without prior extraction. Only a 2-ml volume of urine is necessary. | 18,962,046 |
Chemical separation and spectrographic estimation of rare earths and yttrium in PuO(2) and (U,Pu)O(2). | An emission spectrographic method for the estimation of rare-earth impurities in plutonium oxide and the mixed oxide (U,Pu)O(2) (30% PuO(2)-70% UO(2)) has been developed. Rare-earth impurities are separated from the matrix by solvent extraction with tri-n-octylamine in xylene and are estimated after concentration. Thulium is used as internal standard and LiF-AgCl as carrier. The spectra are excited in a d.c. arc. The detection limits lie in the range 0.004-0.1 mug and the coefficient of variation ranges from 5 to 23%. | 18,962,048 |
Anion-exchange behaviour of metals on deae-cellulose in hydrochloric acid-acetic acid media. | The anion-exchange behaviour of 35 metal ion species on a weakly basic cellulosic ion-exchanger (DEAE-cellulose) in mixed hydrochloric acid-acetic acid media has been investigated. The sorption of metal chloro-complexes on DEAE-cellulose is greatly enhanced with increasing concentration of acetic acid. Differences in sorbability of metals allow many useful analytical separations to be conducted on short columns, containing approximately 1 g of DEAE-cellulose(Cl(-)). Procedures for the chromatographic separations of two-, three-, four- and five-component mixtures are given. | 18,962,056 |
Contributions to the basic problems of complexometry-XXVI determination of calcium in the presence of large amounts of magnesium. | Two methods for the determination of calcium in the presence of very large amounts of magnesium are proposed. Both are based on back-titration of excess of EGTA, Thymolphthalexone being used as indicator. In the one method the titrant is a zinc solution, in the other a calcium solution is used, with a small amount of zinc present for end-point indication. Both titrations can be performed either visually or spectrophotometrically. | 18,962,059 |
Rapid determination of nitrate nitrogen in soils. | A simple but effective method for pretreatment of soil samples is suggested. The application of an electrodynamic vibrator or ultrasonic device eliminates the necessity for continuous stirring in direct potentiometric determination of nitrate nitrogen. It also makes the extraction process faster, and the apparatus could easily be used in automatic systems for continuous soil control. | 18,962,068 |
Direct atomic-absorption spectrometric analysis of geological materials-a review. | A review is given of the problems likely to be encountered in the atomization of solid samples of geological materials, and of the applications of this technique. | 18,962,084 |
Spectrophotometric determination of some penicillins with ammonium vanadate. | A spectrophotometric method for determining some penicillins has been developed. A known volume of the penicillin solution-in phosphate buffer of pH 6.8 is boiled with ammonium vanadate solution-in sulphuric acid medium-for 10 min and the absorbance of the colour formed is measured at 750 nm. The excess of vanadate can also be determined volumetrically. The method has been successfully applied for the determination of penicillin G sodium, phenoxymethyl penicillin, ampicillin sodium, phenethicillin potassium, cloxacillin sodium and methicillin sodium. The procedure is also used for analysing some pharmaceutical preparations of these drugs, e.g., injections. The results obtained are in agreement with those of the B P 1973 methods. | 18,962,095 |
High-precision gravimetric coulometry using the silver-perchloric acid coulometer: Titration of arsenious oxide with electrogenerated iodine. | High-precision gravimetric coulometry with a silver-perchloric acid coulometer is evaluated as an alternative to the conventional titrimetric method. The loss of weight (caused by electrolytic dissolution) of a highly pure silver anode in series with the cathode of a conventional constant-current titration system is measured and related to the number of equivalents of substance titrated. The precision of the method is determined by titrations of the Standard Reference Material 83C arsenious oxide (99.99% pure) with electrogenerated iodine, using biamperometric end-point detection. Depending on the size of the sample, an ultimate precision of 25 ppm is obtained. The assay for 0.5-g samples of the SRM material is 99.993(9) +/- 0.002(5)% purity. | 18,962,104 |
Estimation of methionine and its metal complexes by oxidation with chloramine-T and dichloramine-T. | A simple method for the estimation of methionine (HMt) in aqueous solution has been developed, based on its oxidation with chloramine-T and dichloramine-T at room temperature. The direct titration, with visual or potentiometric end-point involves a two-electron change, corresponding to the formation of methionine sulphoxide. Most amino-acids do not interfere, but cysteine, glutathione and thiourea are oxidized under these conditions. A back-titration procedure in which methionine is oxidized in 0.1M sodium hydroxide by excess of chloramine-T with a four-electron change corresponding to the formation of methionine sulphone has also been developed. Methionine is oxidized to the respective nitrile, however, with excess of dichloramine-T. The methods have also been employed in estimating methionine in two of its soluble complexes, [NiMt]ClO(4) and Na[AgMt(2)]. | 18,962,124 |
[Not Available]. | The sample (up to 5 mg) is destroyed by using a wet process in a glass flask of the Kjeldahl type. Aluminium cobalt, tin and iron are determined spectrophotometrically. The following reactions are used: complexation of aluminium by Alizarin Red S and calcium cobalt(II) by tiron tin(IV) by phenylfluorone, iron(III) by tiron. | 18,962,127 |
Analytical application of organic reagents in hydrophobic gel media-IV Selective preconcentration of Cobalt(II) with 1-nitroso-2-naphthol gel. | Cobalt is selectively extracted from solution onto gel beads impregnated with 1-nitroso-2-naphthol. A concentration factor of 67 has been achieved by passing 2 litres of sea water containing 0.05 ppm of cobalt over the beads at a flow-rate of 40 ml/hr. The cobalt is eluted from the beads with methyl isobutyl ketone. | 18,962,134 |
A new ion-exchange test for detection of ketones on the microgram scale. | A test for the detection of certain ketones is based on the reaction with 1-chloro-2,4-dinitrobenzene in the presence of an anion-exchange resin in the OH(-) form, to give a violet colour on the resin bead surface. | 18,962,137 |
Microscopic acid dissociation constants of 3,4-dihydroxyphenylpropionic acid and related compounds, and 3,4-dihydroxyphenylalanine (DOPA). | The dissociation constants of 3,4-dihydroxyphenylpropionic acid and related compounds and of DOPA were determined by potentiometric titration and complementary tristimulus colorimetry at 25 degrees and mu = 0.1 (NaClO(4)) in aqueous solution. The thermodynamic parameters were calculated from the values of the dissociation constants at various temperatures. The dissociation constants and corresponding thermodynamic parameters for the first phenol group of the catechols showed almost the same values as those of the phenol derivatives. In the dissociation of the second phenol group of the catechols, formation of an intramolecular hydrogen bond was indicated. The microscopic acid dissociation constants of 3,4-dihydroxyphenylacetic acid and 3,4-dihydroxyphenylpropionic acid were calculated by two different methods. In the physiological pH-region (pH 7.2-7.4), 3,4-hydroxyphenylpropionic acid is present in the carboxylate form, and the two possible monophenolate anions are present to the extent of about 45% and 40%, respectively, at pH 11.0. The twelve micro-constants for the eight chemical species from DOPA were similarly evaluated. | 18,962,144 |
[Not Available]. | Metal phosphorothioates are titrated in acetone, acetonitrile and dimethylformamide with potassium hydroxide, with potentiometric detection. They can be titrated in the presence of the corresponding phosphorothioic acids in the dimethylformamide. | 18,962,148 |
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