FLOW-INJECTION SPECTROPHOTOMETRIC DETERMINATION OF OXALATE, CITRATE AND TARTRATE BASED ON PHOTOCHEMICAL-REACTIONS

A flow-injection configuration for the spectrophotometric determinatio n of oxalate, citrate and tartrate is proposed. The procedure is based on the photochemical decomposition of the complexes formed between ir on(III) and these anions. The iron(II) produced in the photochemical r eactions was detected by measuring the absorbance after complexation w ith ferrozine (lambda(max) = 562 nm). Linear calibration graphs were o btained over the concentration ranges 5.0 x 10(-6) - 1.0 x 10(-4) M, 8 x 10(-6) - 1.8 x 10(-4) M and 1.0 x 10(-6) - 2 x 10(-5) M for oxalate , citrate and tartrate, respectively. The relative standard deviations at the 1 x 10(-5) M concentration level were within the range 1.29 - 1.47%. The sampling frequency was about 40 samples h(-1). The usefulne ss of the method was tested in the determination of oxalate in urine a nd spinach, of citrate in pharmaceuticals and soft drinks and of tartr ate in pharmaceuticals. For the determination of oxalate in urine samp les a prior separation of the analyte by precipitation with calcium ch loride is recommended.