Introduction of hydrogen peroxide as an oxidant in flow injection analysis: speciation of Cr(III) and Cr(VI)

Hydrogen peroxide was used as an oxidant in Flow Injection Analysis (FIA). The formation of gaseous components during the analysis was suppressed by maintaining the concentration of hydrogen peroxide lower than 0.15% in 0.1 M NaOH. By this method, Cr(III) was oxidised on-line to Cr(VI) which was detected spectrophotometrically at 548 nm by complexation with 1,5-diphenylcarbazide (DPC). Linear responses were found for concentrations <20 mg/l and the sensitivities obtained of the pure species were 0.0225±0.0015 l/mg for Cr(III) and 0.0420±0.0015 l/mg for Cr(VI). For the speciation of Cr(III) and Cr(VI), the analysis of both species was performed by treating them as mutual interferences. Thus, the total amount of chromium species was measured by FIA and the total amount of chromium was measured by Graphite Furnace Atomic Absorption Spectrometry (GFAAS). The speciation was performed at concentrations above 6 mg/l which is suitable for on-line monitoring of e.g. waste waters.