SPECIATION OF ARSENIC BY ION CHROMATOGRAPHY AND OFF-LINE HYDRIDE GENERATION ELECTROTHERMAL ATOMIC-ABSORPTION SPECTROMETRY

Arsenic species including arsenite (As(III)), arsenate (As(V)), arsenobetaine (AB), monomethylarsenate (MMA), dimethylarsenate (DMA), p-aminophenylarsenate (p-APA) and arsenocholine (AC) have been separated on an anion- and a CAS1 ion-exchange column connected in series. Arsenite co-elutes with arsenobetaine. The mobile phase used was 5 mmol l-1 NH4H2PO4 solution (pH 5.8) at the flow rate of 1 ml min-1. Arsenic species in the fractions that eluted from the columns were determined by hydride generation atomic absorption spectrometry (AAS). A thermal decomposition procedure was introduced to convert the organoarsenicals, such as arsenobetaine and arsenocholine, into As(V), which can be reduced by sodium tetrahydroborate to form arsenic hydride, and then trapped on a palladium-coated graphite tube, followed by AAS detection. Arsenobetaine which co-elutes with As(III) can be determined by substracting the amount of As(III) determined from the total amount of As(III) plus arsenobetaine after thermal decomposition. Detection limits (3sigma signal-to-noise) were 1.6 ng ml-1 for As(III), As(V), MMA and p-APA and 1.9 ng ml-1 for DMA, AB and AC for a 0.1 ml injection. The proposed method has been applied to the determination of arsenic species in spiked lake water and river water.