Determination of trace amounts of oxalate in vegetable and water samples using a new kinetic-catalytic reaction system.

This paper describes a new, simple, sensitive, and selective catalytic-kinetic-spectrophotometric method for the determination of trace amounts of oxalate in vegetable and water samples. The method is based upon the catalytic effect of oxalate on the oxidation of crystal violet (CV) by dichromate in sulfuric acid media. The reaction was followed by measuring the decrease in absorbance of CV at 630 nm (lambdamax of CV). The dependence of sensitivity on the reaction variables was studied and discussed. Under the optimum conditions, a fixed time procedure was used to obtain a linear calibration curve in the oxalate concentration ranges of 0.20-5.5 microg mL(-1) of oxalate. The calculated detection limit was 0.050 microg mL(-1). The relative standard deviations for ten replicate determinations of 0.40, 1.8, and 2.5 microg mL(-1) of oxalate were 6.0%, 2.5%, and 1.8%, respectively. The effect of the presence of various species commonly associated with real samples was also investigated. The proposed method was successfully applied for the determination of oxalate in vegetable and spiked water samples.