Flow-Injection Spectrophotometric Determination of Oxalate,Citrate and Tartrate Based on Photochemical Reactions

Abstract

A flow-injection configuration for the spectrophotometric determination of oxalate, citrate and tartrate is proposed. The procedure is based on the photochemical decomposition of the complexes formed between iron(III) and these anions. The iron(II) produced in the photochemical reactions was detected by measuring the absorbance after complexation with ferrozine (λ_max=562 nm). Linear calibration graphs were obtained over the concentration ranges 5.0 × 10^?6 - 1.0 × 10^?4 M, 8 × 10^?6 - 1.8 × 10^?4 M and 1.0 × 10^?6 - 2 × 10^?5 M for oxalate, citrate and tartrate, respectively. The relative standard deviations at the 1x10^?5 M concentration level were within the range 1.29 - 1.47 %. The sampling frequency was about 40 samples h^?1. The usefulness of the method was tested in the determination of oxalate in urine and spinach, of citrate in pharmaceuticals and soft drinks and of tartrate in pharmaceuticals. For the determination of oxalate in urine samples a prior separation of the analyte by precipitation with calcium chloride is recommended.