A new and sensitive method for the determination of trace arsenic using differential pulse polarography

Abstract

A new and simple differential pulse polarographic method has been developed for the trace determination of arsenic. When selenite was added into solutions of some ions such as copper, lead, cadmium, zinc, and chromium, their differential pulse polarographic peak decreased. A new reduction peak appeared at a more positive potential than the ion present and it was always higher than the corresponding reduction peak of the ion. Thus, we made use of this interference for the trace determination of As(III). By the addition of selenite onto As(III), a new As−Se intermetallic compound peak was formed at about −0.35 V (pH at about 1.0–2.0). The trace arsenic concentration could be determined simply from this peak by the addition of standard arsenic into a polarographic cell. In the presence of large amounts of selenite, 2 × 10−7 mol/L As(III) could be determined from this peak precisely. With the newly established method, the limit of detection was 1 × 10−8 mol/L (S/N = 3). Among the most common cations and anions, only Cd−Se and Pb−Se intermetallic compound peaks had an overlap with the As−Se peak. This interference could be eliminated simply by the addition of EDTA. This method was applied successfully for the determination of arsenic in a digested beer sample.