Redox speciation of inorganic arsenic in water and saline samples by adsorptive cathodic stripping voltammetry in the presence of sodium diethyl dithiocarbamate

摘要

This paper describes a new voltammetric procedure for the inorganic speciation of As(III) and As(V) in water samples. The procedure is based on the chemical reduction of arsenate [As(V)] to arsenite [As(HI)] followed by the voltammetric determination of total arsenic as As(III) at the hanging mercury drop electrode (HMDE) by adsorptive cathodic stripping voltammetry (AdCSV) in the presence of sodium diethyl dithiocarbamate (SDDC). The reduction step involved the reaction with a mixture of Na2S2O5 and Na2S2O3 in the concentrations 2.5 and 0.5 mg mL(-1), respectively, and the sample heating at 80 C for 45 min. The linear range for the determination of total arsenic as As(III) in the presence of SDDC was between 5 and 150 mu g L-1 for a deposition time of 60 s (r=0.992). A detection limit of 1.05 mu g L-1 for total As was calculated for the method in water samples using a deposition time of 60 s. The detection limits of 4.2 mu g L-1 and 15.0 mu g L-1 for total As in seawater and dialysis concentrates, respectively, were calculated using a deposition time of 60 s. The relative standard deviations calculated were 2.5 and 4.0% for five measurements of 20 mu g L-1 As(V) as As(III) in water and dialysis concentrates, respectively, after chemical reduction under optimized conditions. The method was applied for the determination of As(III) and total As in samples of dialysis water, mineral water, seawater and dialysis concentrates. Recovery values between 86.0 and 104.0% for AS(III) and As(V) added to the samples prove the satisfactory accuracy and applicability of the procedure for the arsenic monitoring.