Measurement of ultratrace levels of chromium by adsorptive–catalytic stripping voltammetry in the presence of cupferron

Abstract

An ultrasensitive adsorptive–catalytic stripping (voltammetric and potentiometric) procedure for determining trace levels of chromium in the presence of cupferron is described. The method offers higher sensitivity than previous adsorptive stripping schemes for chromium. Optimum experimental conditions were found to be a 1 × 10^–3 mol l^–1 piperazine-N,N′-bis(ethanesulfonic acid)(PIPES) solution (pH 7.0) containing 1 × 10^–4mol l^–1 cupferron and a preconcentration potential of –0.82 V. A preconcentration time of 1 min results in a detection limit of 1.0 ng l^–1. The relative standard deviation at 100 ng l^–1 is 2.4%(n= 20, for 20 s preconcentration). The stripping potentiometric scheme allows convenient measurements of chromium in the presence of dissolved oxygen. The identical stripping response for chromium(III) and chromium(VI) solutions makes the method applicable to the measurement of the total chromium content. The simultaneous determination of chromium and uranium is illustrated. The merits of the proposed procedure are demonstrated by the analysis of soil and groundwater samples.