Selective kinetic-spectrophotometric determination of trace amounts of As(III) based on an induction period

A new, selective, sensitive, and simple kinetic spectrophotometric method is proposed for the determination of As(III) in the presence of As(V) in alloys and water samples. This method is based upon the inhibiting effect of As(III) on the redox reaction between sodium periodate and meta-cresol purple (MCP) in acidic media. The reaction induction period is proportional to the concentration of As(III). The decolorization of MCP is used to monitor the reaction spectrophotometrically at 525 nm. As(III) can be determined in the range of 0.08–3.0 μg mL^-1 under optimum conditions. The detection limit of the method with 3σ criteria is 0.08 μg mL^-1. The relative standard deviations for eight replicate determinations of 0.20, 0.60, and 0.80 μg mL^-1 As(III) are 5.0%, 4.8%, and 1.9%, respectively. The recovery percentage ranges from 96.0% to 103.3%. The influence of various foreign species is also studied; As(V) does not interfere with the As(III) measurement even when present in1000-fold greater than As(III). This method can successfully be used to determine As(III) concentration in synthetic alloys and spiked water samples.