Abstract
A two-step solvent extraction preconcentration procedure in combination with FI-HGAAS is described for the ultra-trace determination of arsenic in environmental samples. Arsenic(III) was quantitatively extracted from natural water sample at pH 1.5 in the presence of 10 % (m/v) thiourea (masking agent) with 10 ml of 0.2 % (m/v) zinc hexamethylenedithiocarbamate in 2,6 dimethyl-4-heptanone (DIBK) and subsequently back-extracted with slight stoichiometry excess of Cu(II) solution. Total arsenic was extracted using the same procedure after reducing the As(V) to As(III) with sodium thiosulphate. The arsenic concentration in the aqueous back-extracts were determined by FI-HGAAS. The concentration of As(V) was then determined by subtracting the concentration of As(III) from that of the total As. The recovery of As from water samples spiked with 100 ng of As(III) and As(V) were 95.5 - 99.7 %. The detection limit (3 σ) was 0.008 μg 1 -1 and the precision (RSD) was 4.5 % (n = 8) at the 0.5 μg 1 -1 level.
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