EFFECT OF ONLINE COMPLEX-FORMATION KINETICS ON THE FLOW-INJECTION ANALYSIS SIGNAL - THE SPECTROPHOTOMETRIC DETERMINATION OF CHROMIUM(VI)

The sensitivity of the flow injection analysis (FIA) method for determination of chromium(VI) using 1,5-diphenylcarbazide (DPC) depends on the concentration of the acid used in confluence with the DPC solution. At low acid concentrations slower on-line reaction kinetics are observed for Cr - DPC complex formation. Hence the chemical contribution to the over-all dispersion value cannot be ignored. This indicates that the best experimental conditions for the static procedure may not always translate directly to the dynamic conditions of FIA. In the present instance the maximum signal is obtained with acid concentrations at or above 0.80 M. Although sulphuric acid may be used, as in the conventional procedure, the best working conditions are achieved using nitric acid.