. Can. J. Chem. 61, 2795 (1983.Titrimetric and spectrophotometric methods are developed for the estimation of oxalate at mmole and micromole ranges, respectively. In these methods thallium(II1) is used as the oxidant and the reduced thallium(1) is determined oxidimetrically by potassium bromate in the titrimetric method and by measuring the optical density of thallium (II1)
IntroductionThe unique properties like acidity, reducing capacity, and chelating ability of oxalic acid and oxalates made them a very useful class of compounds in industry as well as in analytical chemistry. Oxalates occur widely in many biological systems. The various spectrophotometric, solubility, kinetic, ion exchange, solvent extraction, potentiometric, polarographic, and other methods for the determination of oxalates were reviewed by Murty and Hams (1). Rao and Aravamudan (2) have surveyed the available methods for the determination of oxalic acid and described a new method utilising the photochemical reaction between iron(II1) and oxalic acid, titrating the iron(I1) formed by sodium vanadate. The advantages claimed by the authors over other methods are (i) no heating is required and (ii) formic acid will not interfere in the method. Riggs and Bricker (3) have extended the same idea and estimated oxalic acid at mg level by titrating the iron(I1) formed using potassium dichromate stating that its interference with organic substances is tolerable. However, they pointed out that an inert atmosphere is necessary to avoid the air oxidation of iron(I1) formed during the reactiop; about this Rao and Aravamudan have not mentioned anything. Rao et al. (4) avoided the use of dichromate because of the induced oxidation of oxalic acid in the presence of iron(II), they preferred sodium vanadate as the oxidant.Riggs and Bricker followed the progress of the reaction with the time of irradiation by estimating iron(I1) formed with dichromate. If the view expressed by Rao et al. regarding the induced oxidation of oxalic acid by dichromate was correct the values reported by these authors were prone to error especially in reporting the interferences.Using the same photochemical reaction Cooley and Kratochvil (5) have described a method for the determination of oxalate using a C 0 2 electrode detector. Later using the same reaction they described another method (6) using a gas chromatographic technique for measuring C02, and claimed that this method is less expensive and rapid and also subject to fewer interferences compared to their first method. They reported obtaining values with an accuracy of about 2%.In the light of the above reports the present authors have attempted to suggest simple and convenient methods for the estimation of oxalic acid in the presence of other organic acids
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