Flow injection method for the determination of arsenic(III) at trace levels in alkaline media

Abstract

A flow injection (FI) method for the determination of trace levels of trivalent arsenicals in environmental samples is reported. The method is applicable to arsenic compounds that can be base hydrolysed to yield arsenious acid, which is then detected electrochemically. By using the constant-current mode of potentiometric stripping analysis (PSA), a method was developed for the determination of arsenious acid in basic media at Ep ≈–475 mV versus Ag/AgCl (3 mol l^–1 NaCl). The method parameters were optimized, including pH, supporting electrolyte, deposition potential, deposition time, stripping current and stripping delay. Additionally, possible electrochemical interferences, including As^V, Bi^III, Cd^II, Cu^II, Hg^II, Pb^II, Sb^III, Se^IV and Sn^II, were studied. A detection limit of 0.21 µg l^–1 was achieved for As^III in aqueous samples (100 µl) over the range 0.10–50 µg l^–1 in the stopped-flow FI manifold. The precision (RSD) of the method at 5 µg l^–1(n= 8) is <5%. The method was applied to the indirect determination of dichloro(2-chlorovinyl)arsine (Lewisite), a chemical warfare agent that is difficult to measure in the environment because it rapidly decomposes to form its geminal diol, 2-chlorovinylarsonous acid (CVAA). CVAA can be base hydrolysed to form arsenious acid for detection by FI–PSA.