Cathodic Stripping Voltammetric Study for Determination of Inorganic Arsenic Species in Seaweed Gracilaria fisheri

A simple, rapid, selective and sensitive square wave cathodic stripping voltammetry (SWCSV) at a hanging mercury drop electrode (HMDE) for the determination of As(III), As(V) and inorganic As(total) in seaweed was developed. The method was based on the formation of copper-arsenic intermetallic compound in the presence of HCl onto a HMDE at a constant potential of -0.40 V vs. Ag/AgCl in the deposition step, followed by the reduction of deposited compound to arsine at a potential of -0.78 V in the stripping step. In the system, only As(III) was directly measured, whereas inorganic As(total) was measured by reducing As(V) to As(III) using thiosulfate. In the deposition step, the use of 10 mg L-1 Cu(II) and 1 M HCl was recommended for the determination of 2 µg L-1 As(III) under the optimum instrumental variables obtained at 150 s for deposition time and 2000 rpm for stirring speed with the highest deposition efficiency of 16.15 and 88.49%, respectively. In the determination of As(V), two values of the highest reduction efficiency obtained using concentration of 40 mg L-1 thiosulfate, and reducing time at 300 s were 98.15% and 37.89%, respectively. In the measurement, the quantification limits of As(III) and As(V) were 0.46, and 1.62 µg L-1, respectively. The relative standard deviation (n=10) for 2 ug L-1 As(III) and As(V) were 5.20% and 2.57%, respectively. The proposed method was applied to the determination of inorganic arsenic species in seaweed Gracilaria fisheri.