SPECIATION OF ARSENIC BY THE DETERMINATION OF TOTAL ARSENIC AND ARSENIC(III) IN MARINE SEDIMENT SAMPLES BY ELECTROTHERMAL ATOMIC-ABSORPTION SPECTROMETRY

A method for the determination of arsenic(III) and total arsenic was studied. Arsenic(III) was chelated with 2% sodium diethyldithiocarbamate in water, extracted with isobutyl methyl ketone and determined by electrothermal atomic absorption spectrometry, using palladium as chemical modifier. The effects of pH, extraction time and amounts of reagents required for the extraction were studied. The detection limit of this method was 25 mu g kg(-1). Different modifiers [LaCl3-HNO3, Pd-Mg(NO3)(2)] for the total arsenic determination in slurries of marine sediment samples were also investigated; LaCl3-HNO3 was avoided because a double peak was observed. The detection limit for the determination of total arsenic using Pd-Mg(NO3)(2) as modifier was 44 mu g kg(-1). The precisions obtained for the different amounts of arsenic(III) and total arsenic mere 0.57-2.99 and 0.83-0.45%, respectively. The graphite furnace programmes, accuracy and interferences for both procedures were also studied. The method has been applied to the determination of arsenic(III) and total arsenic in sediment samples from Galicia (North West of Spain).