Positive ion electrospray mass spectra of arsenobetaine, AB, arsenocholine, AK, monomethylarsonic acid, MMA, dimethylarsinic acid, DMA, tetramethylarsonium TMAs, arsenate, AsV, and arsenite, AsIII, have been obtained. When appropriate, negative ion electrospray mass spectra have been performed. In order to clarify fragmentation pathways MS/MS spectra have also been recorded. Positive ion electrospray mass spectra have been found to be more useful for the identification of the organoarsenic compounds AB, AK, MMA, DMA and TMAs, whereas negative ion electrospray mass spectra is more suitable for the identification of the inorganic compounds AsV and AsIII. © 1997 John Wiley & Sons, Ltd.

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Total digestion of estuarine water samples by dry ashing shows that a significant fraction of dissolved arsenic does not form hydrides with sodium tetrahydroborane (NaBH,) and is therefore not detected by the normal hydride generation-atomic absorption analytical technique. It is also refractory to alkaline digestion with sodium hydroxide. Sequential ultrafiltration suggests a molecular weight below 210 for this new arsenic fraction. The magnitude and molecular weight of this fraction may open new perspectives on the biogeochemica1 cycling of arsenic. Ecological reasons can explain the discrepancy between these findings and previous research.

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