Determination of arsenic(III) and total arsenic(III,V) in water samples by resin suspension graphite furnace atomic absorption spectrometry

A preconcentration method of arsenic(III) using ammonium pyrrolidinedithiocarbamate (APDC) and a finely divided anion-exchange resin is described for the determination by graphite-furnace atomic absorption spectrometry (GFAAS). The method is based on the extraction of the As(III)-APDC complex on the resin phase at pH 1.2, separation of the resin particles by filtration, dispersion of them in 1.0 ml of 0.1 mol l(-1) nitric acid containing 50 mu g of nickel(II), and introduction of the suspension to a graphite furnace. The detection limit of arsenic in a 150-ml sample aliquot was 1.0 ng (6.7 ppt), based on three times the standard deviation of the blank. Total inorganic arsenic(III,V) was extracted similarly after the reduction of As(V) to As(III) with sodium thiosulfate. The interfering ions, such as Cu(II), Pb(II) and Sn(II), could be removed by extraction as the respective APDC complexes at pH 5, where neither As(III) nor As(V) were extracted. Arsenic(III) and total As(III,V) in the filtrate were then extracted at pH 1.2 in the absence or presence of sodium thiosulfate, respectively. The proposed method was applied to the determination of As(III) and total inorganic As(III,V) in hot spring water, seawater, river and tap water samples.