Electrodeposition and stripping voltammetry of arsenic(III) and arsenic(V) on a carbon black-polyethylene composite electrode in the presence of iron ions

In this work, a new sensor is proposed for the stripping voltammetric determination (anodic stripping voltammetry-ASV) of total arsenic(V) or arsenic(III). The sensor is based on an Fe-modified carbon composite electrode containing 30 % carbon black-high-pressure polyethylene (CB/PE). The modification with iron is achieved by the addition of Fe(III) or Fe(II) ions to the sample solution and co-electrodeposition of iron and arsenic on the CB/PE electrode. In anodic stripping voltammetry, two peaks are observed: an Fe peak at -0.45 or -0.29 V and a peak at 0.12 +/- 0.07 V which depends on the arsenic concentration and corresponds to the As(0) -> As(III) oxidation, as is the case with other solid electrodes. The optimum conditions proposed for ASV determination of As(V) and As(III) in solutions in the presence of dissolved oxygen are the following: the background electrolyte is 0.005 M HCl containing 0.5-1 mg/ L Fe(III) for As(V) and containing 1.0-1.5 mg/ L Fe(III) for As(III), respectively; E (dep) = -2.3 V; rest period at -0.10 V for 3-5 s before the potential sweep from -0.2 to +0.4 V; scan rate is 120 mV/ s. The detection limit (LOD, t = 120 s) for As(III) and As(V) is 0.16 and 0.8 mu g/ L, respectively. Various hypotheses on the effect of Fe ions and atoms on the electrodeposition and dissolution of arsenic are considered. The new method of determination of As(III) and As(V) differs from known analogues by its simplicity, low cost, and easy accessibility of the electrode material. It allows the voltammetric determination of total arsenic after chemical reduction of all its forms to As(III) or after their oxidation to As(V).