Batch square-wave voltammetric and flow-injection amperometric determination of trace amounts of bromofenoxim

Abstract

Two sensitive and rapid methods, batch voltammetric and flow- injection analysis (FIA) with amperometric detection are reported, for trace determination of the herbicide bromofenoxim. Preliminary results on its electrochemical behaviour are presented as well. While bromofenoxim did not exhibit any response at bare solid electrodes, two well-defined voltammetric reduction peaks were obtained at mercury electrodes. Both peaks, with peak potentials at −0.38 V and −0.54 V vs. Ag AgCl in pH 7 Britton-Robinson buffer, appear as a consequence of a reduction of the two nitro groups of bromofenoxim, and show strong adsorption nature. The first peak, at the less negative potential, was found to be more sensitive and was therefore utilised for the voltammetric determination of bromofenoxim. In direct batch voltammetric analysis at a dropping mercury electrode by applying square-wave voltammetry (SWV), linearity between SWV signal and bromofenoxim concentration was found to exist from 0.5 μg/l to 600 μg/l (1.1 × 10 −9 mol/l to 1.3 × 10 −6 mol/l), with an estimated limit of detection of 0.1 μg/1. Dynamic properties and in situ formation of the mercury film coated glassy carbon electrodes were also investigated for the determination of bromofenoxim in flow- injection systems. Employing FIA with amperometric detection at an operating potential of − 0.7 V vs. Ag AgCl , the signal response was linearly dependent on the bromofenoxim concentration within the range from 50 μg/l to 4000 μg/l (1.1 × 10 −7 mol/l to 0.9 × 10 −5 mol/l) and a detection limit (3σ) of 10 μg/l (0.4 ng absolute, 40 μl) was obtained. Optimisation of parameters for the amperometric detection of bromofenoxim and utilisation of the proposed methods are presented and discussed.