FIRST-ORDER SPECIATION OF AS USING FLOW-INJECTION HYDRIDE GENERATION ATOMIC-ABSORPTION SPECTROMETRY WITH IN-SITU TRAPPING OF THE ARSINE IN A GRAPHITE-FURNACE

A simple method is described to distinguish between As species that re act with sodium tetrahydroborate (III) to form AsH3 and the naturally occurring As species that are unreactive. Results for this rudimentary or ''first order'' speciation scheme are reported for biological tiss ue, aquatic plant material, urine and natural water samples. Biologica l tissue and aquatic plant samples were briefly solubilized in a mixtu re of 50% nitric acid, no sample preparation was required for the urin e or natural water samples. Organoarsenic species which do not react w ith sodium borohydride under acidic conditions such as arsenobetaine, arsenocholine and tetramethylarsenic, are converted to As(V) by on-lin e photo-oxidation or microwave heating in a mixture of 0.5 M NaOH and 0.05 M K2S2O8. The sample is subsequently acidified, reduced with sodi um borohydride and the generated arsine is trapped in a heated graphit e furnace prior to atomization. The superior detection limit (0.14 ng) of the trapping technique permits the dilution of most types of sampl es, minimizing or eliminating interference effects. Without photolysis or microwave heating a combined result for As(III), As(V), monomethyl arsonic acid (MMA) and dimethylarsinic acid (DMA) is obtained. Results are reported for the first order speciation of As in a suite of certi fied reference materials (CRMs) including National Research Council (N RC) biological tissues and natural water samples, Community Bureau of Reference (BCR) aquatic plant materials and the National Institute of Standards and Technology (NIST) SRM 267ON urine sample. The determinat ion of a non-hydride forming As fraction in untreated urine and natura l water certified reference materials (CRMs) has revealed a species of As previously undetected in NRC seawater CRMs.