INDIRECT SPECTROPHOTOMETRIC DETERMINATION OF COMPLEXING AGENTS BY FLOW-INJECTION ANALYSIS BASED ON REDOX REACTION OF COPPER(II) WITH IRON(II)

An indirect spectrophotometric continuous-flow method is presented for the determination of trace amounts of complexing agents such as EDTA, DTPA, CyDTA, EDTA-OH, NTA, citrate and Pyrophosphate. It is based on the accelerating effect Of complexing agent on the rate of the redox reaction of copper(II) with iron(II) in the presence of neocuproine. In this redox system, a copper(I)-neocuproine complex (lambda(max) = 454 nm) is produced, the concentration of which is proportional to the concentration of the complexing agent. Complexing agents at the 10(-6)-10(-5) mol l-1 level can be determined at a rate of 180 samples h-1. The determination of EDTA, NTA and pyrophosphate in mixtures was also studied.