An online preconcentration system for speciation analysis of arsenic in seawater by hydride generation flame atomic absorption spectrometry

In this paper, an on-line preconcentration system has been proposed for speciation analysis of inorganic arsenic in seawater. It is based on the selective reaction of As(III) with ammonium pyrrolidine dithiocarbamate (APDC) followed by sorption of the formed complex under a minicolumn containing polytetrafluoroethylene (PTFE). Afterward, arsenic sorbed has been eluted using a 2 mol L-1 hydrochloric acid solution. The preconcentration system was optimized employing multivariate techniques. A two-level full factorial design and a Doehlert matrix were performed to determining the critical conditions of the factors: the acidity of the sample, APDC concentration, and sample flow rate. So, the procedure using the optimized conditions allows the determination of As(III) with limits of detection and quantification of 0.02 and 0.07 mu g L-1. Total arsenic has been determined after reduction of As(V) using thiourea in acid media and the limits achieved were 0.03 and 0.09 mu g L-1, for detection and quantification, respectively. The precision estimated as the relative standard deviation (RSD) was 5.3%, which was calculated using seven replicates of As(III) solution with a concentration of 0.50 mu g L-1. The accuracy of the method was confirmed by the analysis of the certified reference material CASS-4 seawater furnished by the National Research Council of Canada-NRCC. The system proposed was employed for speciation analysis of arsenic in five seawater samples collected from Todos os Santos Bay, Salvador, Brazil. The As(III) contents obtained varied from 0.09 to 0.51 and the total arsenic contents varied from 0.20 to 0.66 mu g L-1. The results are in agreement with other data reported in the literature.