Dosage de l'acidite libre dans les solutions aqueuses concentrees de plutonium(IV)

A method for the determination of free acidity in concentrated aqueous solutions of plutonium (IV) is described. The plutonium-EDTA complex is formed by addition of the calcium-EDTA complex and the neutralization titration with sodium hydroxide is followed potentiometrically, the equivalence point being determined by a graphical method. The relative standard deviation is 1%. Uranium and iron in small amounts do not interfere. The method is applicable to solutions which are ca, 1 N in acid and which contain up to 200 g Pu/l.     

Determination of Hydroxyl Groups in Epoxy Resins by Potentiometric Titration Using a Reaction with Maleic Anhydride

A reaction of maleic anhydride with epoxy–dian resins in methyl ethyl ketene was investigated. It was shown by potentiometric titration that the resulting maleic esters are stable to hydrolysis in acid and weakly acid organic solutions. This reaction can be used for the quantitative determination of hydroxyl groups in epoxy resins. Epoxy groups do not interfere with the formation of maleic esters under the conditions of determination. The optimal reaction conditions were found. The reaction kinetic was investigated, the reaction rate constants were determined at various temperatures, and the activation energy was found. The value of the activation energy indicates that the reaction is characterized by a low potential barrier.     

The determination of mercury in organic compounds

The micro oxygen-flask combustion technique in combination with the sodium diethyldithiocarbamate titration is a rapid and useful method for determination of mercury in organic compounds. Chlorine and bromine do not interfere; iodine does. When the organic compound contains both mercury and chlorine, the chloride ions can be titrated argentometrically in the same absorption solution after the titration of mercury.     

Titration of sulphides and thiols in natural waters

The concentrations of the species present during the procedure of Boulègue for determination of sulphide, thiols, thiosulphate and sulphite in mineral waters by titration with mercury(II) chloride have been calculated and functions suitable for the evaluation of the equivalence points have been derived. It is shown that the halide ions in seawater interfere only in the titration of sulphite.     

Amperometry with Two Polarizable Electrodes. Chelometric Determination of Rare Earths

Abstract

The method of determining rare earths by chelometric EDTA titration with biamperometric end-point indication using two stationary platinum electrodes was studied. The convenient pH range for the determination of lanthanum is 5.0 – 8.0, for yttrium 3.5 – 8.0 and for ytterbium 3.0 – 8.0. Rare earths have been determined in the presence of iron and thorium. Iron and thorium can be titrated at pH 1.5 – 2.0 and rare earths of the lanthanum group can be determined by successive titration at pH 5.0. Large amounts of rare earths of the yttrium group interfere with the determination of iron and thorium.     

The determination of carboxyl groups in polyethylene terephthalate

Three methods for the determination of carboxyl groups in polyethylene terephthalate are investigated, viz. (a) dissolution in hot benzyl alcohol, addition of chloroform, and titration with benzyl alcoholic potassium hydroxide solution to the phenol red end-point, (b) dissolution in a mixture of o-cresol and chloroform, and potentiometric titration with ethanolic potassium hydroxide solution, and (c) dissolution in a mixture of o-cresol, chloroform and acetone, and titration with ethanolic potassium hydroxide solution with HF-indication of the end-pointThe three methods yield the same results when applied to several samples of different carboxyl content. For several reasons the potentiometric method is preferred to the other two methods.     

Determination of formates by oxidation with iodine

A selective determination of formates based on oxidation with iodine at 100° in presence of potassium hydrogen tartrate, and final titration with thiosulphate solution, is described. The error is below 0.5% for 25–90 mg of formic acid. Few other organic acids interfere.     

Amperometric titration of palladium, silver and copper with benzimidazol-2-ylmethanethiol, and its application to non-ferrous materials

A method is described for the determination of mg amounts of palladium, silver and copper by amperometric titration with benzimidazol-2-ylmethanethiol in acetate buifer medium (pH 4-5) at an applied potential of -0.2 V vs. the saturated calomel electrode. Direct titrations are possible in the presence of a number of foreign ions. Copper and palladium interfere mutually and in the determination of silver. Mercury(I), mercury(II) and platinum(IV) also interfere. Silver does not interfere in the determination of copper and palladium if it is first precipitated as chloride. The method has been successfully applied to the analysis of non-ferrous materials.     

Non-aqueous quantitative determination of the carbonyl functional group by constant-current potentiometric titration

A non-aqueous direct titration procedure has been developed for the determination of aldehydes and ketones. It uses two platinum-wire indicating electrodes with a constant current of 0.5 muA. The solvent medium is 0.15M sodium perchlorate in tetrahydrofuran. The titrant is sodium fluorenyl in a mixture of 1,2-dimethoxyethane and tetrahydrofuran. All types of carbonyl compounds react with the sodium fluorenyl, but steric hindrance prevents complete reaction with certain ketones containing bulky groups. The lowest concentration of carbonyl that can be determined with acceptable accuracy and precision is 7.5 x 10(-3)M, the error being < 3% and the precision better than +/-2.5%. Most reducible compounds interfere, e.g., peroxides, acid halides, nitro-compounds, acids, and water, and cannot be differentiated potentiometrically. The method can be extended to other reducible functional groups, e.g., nitro groups and acid chlorides.     

Potentiometric titration of Co(II) in presence of Co(III)

A potentiometric titration for cobalt(II) determination in the presence of Co(III) based on the oxidation of Co(II) with Na₂CrO₄ in ethylenediamine medium and back-titration of the oxidant excess with (NH₄)₂Fe(SO₄)₂ in acid medium is described. The titration is monitored with a Pt indicator electrode and carried out until the greatest jump of potential from one drop of titrant appears. A RSD smaller than 1.5% has been obtained for 50–300 μmol Co(II). The method proposed was applied in the analysis of a new type electroless copper plating solutions containing Co(II)-ethylenediamine complex compounds as reducing agents. Cu(II), Co(III) and Cr(III) do not interfere in the determination of Co(II).     

Coulometric titrations with mercury(I) and (II) determinations of secondary amines and mercaptans

A study of the titration of aliphatic amines and mercaptans with electrolytically generated mercury(II) reagent is reported. Amines were titrated after conversion to their corresponding dithio-carbamic acids by reaction with carbon disulfide. Using this procedure, a 3.10^-4F solution of secondary amine was titrated with an accuracy of better than 1% and a concentration of 3.10^-6F with an accuracy of better than 2%. Primary amines constituted an interference in this procedure but were removed prior to the titration with salicylaldehyde. Tertiary amines were found not to interfere. Comparable titrations with generated silver ion did not give quantitative results.The application of electrolytically generated rnercury(II) reagents for the titration of another organic functional group, sulfhydryl, was also studied. The titration of a sulfhydryl compound (cysteine) was studied briefly. Amounts of cysteine down to 1. 29 mg in 100 ml of solution (1.3.10^-4F) were determined with an accuracy of better than 1%. Smaller amounts of cysteine down to 0.26 mg (2.10^-5F) were determined with about 3% accuracy.     

Determination of photolysis constants of some aliphatic amines in the mixed solvent 80% dimethylsulfoxide/20% water and assessment of titration conditions

The pK_b values of some aliphatic amines in 80% dimethylsulfoxide—20% water are reported. The mixed solvent offers worse titration conditions than water for the determination of these bases. The only advantage of using this solvent for titration of bases is its excellent solvating ability.     

Determination of sulfur in organic compounds using a barium-selective electrode

A procedure was developed for determining sulfur (>1.5 abs %) in sulfur-containing organic compounds. The procedure was based on the combustion of a sample portion in a flask filled with oxygen followed by the potentiometric titration of sulfate ions with barium nitrate in a water-acetone solution. In distinction from analogous procedures, halogens and metals contained in the analyzed compound did not interfere with the determination of sulfur. The error of determination was below 3 rel %.     

Oxidimetric determination of methionine and its metal complexes with chloramine-B and dichloramine-B

Simple, rapid, and reproducible methods for the determination of methionine (HMt) and its metal complexes, [NiMt]ClO₄₊ and Na[AgMt₂], in aqueous solutions have been developed, based on their oxidation with chloramine-B and dichloramine-B at room temperature. The direct titration, with a visual or potentiometric endpoint, involves a two-electron change corresponding to the formation of methionine sulfoxide. Several amino acids and common anions and cations do not interfere under these conditions. In the back-titration procedure methionine and its complexes are oxidized by excess CAB in 0.1 N NaOH medium with a four-electron change corresponding to the formation of methionine sulfone. The amino acid and its complexes are, however, oxidized to the respective nitrile, with excess DCB with an eight-electron change.     

Process monitored spectrophotometric titration coupled with chemometrics for simultaneous determination of mixtures of weak acids

A new spectrophotometric titration method coupled with chemometrics for the simultaneous determination of mixtures of weak acids has been developed. In this method, the titrant is a mixture of sodium hydroxide and an acid-base indicator, and the indicator is used to monitor the titration process. In a process of titration, both the added volume of titrant and the solution acidity at each titration point can be obtained simultaneously from an absorption spectrum by least square algorithm, and then the concentration of each component in the mixture can be obtained from the titration curves by principal component regression. The method only needs the information of absorbance spectra to obtain the analytical results, and is free of volumetric measurements. The analyses are independent of titration end point and do not need the accurate values of dissociation constants of the indicator and the acids. The method has been applied to the simultaneous determination of the mixtures of benzoic acid and salicylic acid, and the mixtures of phenol, o-chlorophenol and p-chlorophenol with satisfactory results.     

Amperometry with two polarisable electrodes-XI Determination of bismuth by EDTA titration

Optimum conditions have been found for a highly selective determination of bismuth via EDTA titration with biamperometric indication of the end-point. The influence of the applied potential, pH and stirring on the accuracy and selectivity of the determination has been studied. In a medium of 0.4M nitric acid only high concentrations of iron(III) and copper(II) interfere with the determination of bismuth. Zirconium, thallium(III) and indium interfere even in small concentrations. The average error of the determination of 5-100 mg of bismuth (when titrated with 0.05M EDTA solution) is +/-0-1 % rel. and for the determination of 0.5-10 mg it is +/-0.3% rel. (0.005M EDTA). The method has been verified by the analysis of a Wood's metal of known composition.     

Photometric titration of iron with ethylenediaminedi(o-hydroxyphenylacetic acid)

Fractional mg quantities of ferric iron in 100 ml of solution can be titrated at PH 3.5 with a solution of ethylenediaminedi(o-hydroxyphenylacetic acid). The end-point is found photo- metrically. Errors are generally under 1%, and a number of metals do not interfere. By scaling down the volume of the solution and the titrant concentration, the titration can be extended to μg quantities of iron, and mg quantities are also accessible by changing to a wave length where the sensitivity is not so great. The titration may be useful in certain applications.     

Determination of bismuth(III) by direct potentiometry and potentiometric titration, with an electrode sensitive to Bi(3+)

A liquid-state ion-exchange electrode containing the chelate bismuth(III) complex with 5-mercapto-3-(naphthyl-2)-1,3,4-thiadiazole-2-thione in tetrachloroethane is applied to the determination of bismuth(III) by direct potentiometry and potentiometric titration. The influence of various interfering cations is discussed. In the presence of potassium cyanide as masking agent, Ni(II), Co(II), Cu(II), Ag(I) and Hg(II) do not interfere in the potentiometric EDTA titration. Satisfactory results have been obtained for the determination of bismuth(III) in Wood's metal and two pharmaceuticals.