Analytical aspects of some organic acids

Summary A direct complexometric titration of iron(III) with EDTA using o- and p-cresotic acids indicators is given. The colour change at the end point is from blue-violet to light yellow or colourless [at low concentrations of iron(III)]. The optimum range of pH and temperature for carrying out the titrations is 1.99 to 4.2 and 35° to 55°C and 1.42 to 4.4 and 30° to 60° C, respectively. Iron(III) may easily and accurately be estimated in macro- and micro-gram quantities with the help of these metal indicators. Be, Mg, Ca, Sr, Ba, Cd, UO₂ and Mn are without any interference in the estimation. Back titration procedures for determination of zirconium and thorium with iron(III) and o- and p-cresotic acids are carried out.Part V: See Z. analyt. Chem. 173, 196 (1960).     

Analytical aspects of some organic acids

Summary Back titrimetric procedures for the estimation of aluminium, zirconium, and thorium have been developed, which involved the adjustment of the concentration of the metallic salts, concentration of EDTA,ph, and temperature, addition of indicator solution (namely, 2-hydroxy3-naphthoic acid and back titration with standard 0.1 M ferric chloride solution. This method is based on the fact that the excess EDTA, which is added to the metal solutions may be back titrated with iron(III), which forms a highly coloured complex with the indicator, when present in slight excess. Quantities of aluminium, zirconium and thorium as small as 10.8, 4.6, 11.6 mg respectively, can be back titrated with in experimental error, when present in a volume of 100 ml.Part IV: See Z. analyt. Chem. 172, 356 (1960).     

Analytical aspects of some organic acids

Summary o-Phenylenedioxydiacetic acid has been found to be a selective reagent for the estimation of zirconium. As little as 2.1 mg of zirconium can be easily estimated. The composition of the precipitate varies somewhat and therefore, direct weighing is not possible. This difficulty is overcome by igniting as oxide. Be²⁺, Ca²⁺, Ba²⁺, Zn²⁺, Hg²⁺, Al³⁺, Ce³⁺, Ti⁴⁺, Th⁴⁺, UO²⁺, Mn²⁺, Fe³⁺, Co²⁺, and Ni²⁺, ions do not interfere. Although V₂O₂ ⁴⁺ and Cr³⁺ ions are not precipitated in neutral or slightly acidic solutions they contaminate the zirconium precipitate, at about 0.30 N HCl concentration. The amount of contamination is so small that it is removed by double precipitation. This method gives satisfactory results even in the presence of small amounts of SO₄ ^2–ions.     

Analytical aspects of some organic acids Part III

Summary m-Phenylenedioxydiacetic acid gives a white precipitate with thorium even in the absence of an electrolyte which is quantitative up toph 4. Be²⁺, Mg²⁺, Ca²⁺, Zn²⁺, Pb²⁺ and Mn²⁺ ions are removed by single precipitation and Al³⁺, UO₂ ²⁺ and trivalent cerite earth ions are removed by double precipitation. Sn²⁺, Sn⁴⁺ and Cr³⁺ ions interfere.Part II: See. Z. analyt. Chem.165, 343 (1959).     

Analytical aspects of organic acids

Summary Phenyl acetic acid has been found to be a selective reagent for the estimation of zirconium. The acid gives a white crystalline precipitate which is quantitative between pH values of 3.00 to 5.40. As the composition of the precipitate varies somewhat, direct weighing is not possible and the compound is ignited to the oxide. The ions Be²⁺, Ca²⁺, Sr²⁺, Zn²⁺, Hg²⁺, Pb²⁺, Mg²⁺, Ni²⁺, and Co²⁺ do not interfere, whereas the ions Fe³⁺, UO₂ ²⁺, Cr³⁺, Ba²⁺, Au⁺, Al³⁺, V₂O₄ ²⁺, Ti⁴⁺, Sn²⁺, and Ba²⁺ cause interferences in the estimation.

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Zusammenfassung Zur gravimetrischen Bestimmung von Zirkonium wird Phenylessigsäure empfohlen. Die weiße, kristalline Fällung ist im pH-Bereich 3,00–5,40 quantitativ. Infolge schwankender Zusammensetzung des Niederschlages ist eine direkte Wägung nicht möglich; er wird daher zum Oxid verglüht. Folgende Ionen stören nicht: Be²⁺, Ca²⁺, Sr²⁺, Zn²⁺, Hg²⁺, Pb²⁺, Mg²⁺, Ni²⁺ und Co²⁺; dagegen verursachen Fe³⁺, UO₂ ²⁺, Cr³⁺, Ba²⁺, Au⁺, Al³⁺, V₂O₄ ²⁺, Ti⁴⁺, Sn²⁺ und Ba²⁺ Störungen bei der Bestim mung.

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Part VI: See Z. analyt. Chem. 175, 29 (1960).     

Dissociation constants of some organic acids

Dissociation constants of di(nonylphenyl)dithiophosphoric acid, di(nonylphenyl)phosphoric acid and 9-phenyltetracosansulphuric acid, determined by two methods, are reported.     

Analytical aspects of some azo dyes from chromotropic acid

Summary Nitroso-SNADNS-4, itself a yellow coloured dye in acid medium forms a reddish-pink colouration with thorium in weakly acid solution. The colour is stable for about 24 hours and to a temperature up to 50C. The thorium complex shows maximum absorbance at the wave length 520 m, while that of the dye occurs at 430 m. The maximum intensity of colour of the thorium complex is shown at aph 2.5. The colour system conforms to Beer's law in a wide range of concentration of thorium and presents a reliable method for the spectrophotometric determination of the metal even in presence of a large number of common ions, the ions interfering are: tin, iron, nickel, cobalt, cerium(IV), zirconium, gold, phosphate and fluoride. The average percentage of deviation of the absorbance index in the determination of thorium is 1.14.Part VI: See Z. analyt. Chem. 167, 105 (1959)     

Analytical aspects of some azo dyes from chromotropic acid

Summary Complexometric titration of thorium with di-sodium versenate solution has been carried out using three dyes: SNADNS, di-SNADNS and nitroso-SNADNS obtained from chromotropic acid. Determinations are suitable with these dyes in the p_H range from 2 to 3, the colour changes at the end point are very distinct with nitroso-SNADNS and di-SNADNS while the colour change with SNADNS at the end point is very difficult to detect. Study of interferences revealed that quite a number of elements like, lead, zinc, mercury, cobalt, nickel etc. do not interfere, whereas heavy interference is caused by iron, zirconium, copper, gold and alkaline earths, Thorium may be separated from them by precipitating it with phthalanilic acid obtained from o-anisidine and the thorium salt on breaking with acid may be determined by versene by the same method. This titrimetric method is expected to become more accurate if the final measurement at the end point is made spectrophotometrically rather than visually.     

Capillary Zone Electrophoresis of some organic acids in milk whey

This paper describes a method for analysing some acids of milk whey by Capillary Zone Electrophoresis. After eliminating the whey proteins by ultrafiltration, the whey underwent electrophoretic separation in the presence of anodic electroosmotic flow. The following analytes were detected: citric, orotic, uric, and hippuric acids. A procedure is described for sample preparation and the operating conditions for electrophoretic capillary separation established. Finally, orotic acid is quantitatively determined.     

Titrimetric determination of some organic acids by xenon trioxide oxidation

Aqueous xenon trioxide in acidic or neutral solutions oxidises carboxylic acids quantitatively to carbon dioxide and water. Micro and semimicro amounts of carboxylic acids may be determined by the iodometric titration of the excess of xenon trioxide remaining in the reaction mixture. The optimum time and temperature for the reaction depend on the structure of the acid ; dicarboxylic and hydroxy-carboxylic acids react faster than corresponding monocarboxylic acids. Oxalic and polyhydroxy acids are oxidised within 20 min at room temperature while acetic, maleic, succinic, malonic acids require 2 hr at 40 degrees . Carboxylic acids in amounts less than 100 mug are determined with a coefficient of variation of 4%, which decreases to 1 % for amounts over 250 mug.