Speciation of submicrogram per liter levels of arsenic in water: On-site species separation integrated with sample collection

Speciation of arsenic is crucial for assessing health implications from arsenic ingestion and for effective removal of arsenic from water. We report a method for the speciation of submicrogram per liter levels of arsenic in water. The method incorporates water sample collection with on-site arsenic species separation. The method is based on selective retention of arsenic species on specific solid- phase cartridges followed by selective elution and hydride generation atomic fluorescence analysis of the arsenic species. The use of a membrane filter, a resin-based strong cation-exchange cartridge, and a silica-based strong anion-exchange cartridge allows for the speciation of particulate arsenic and soluble arsenite, arsenate, monomethylarsonate, and dim ethylarsinate species. Detection limit is on the order of 0.05 mu g/L. The method is suitable for direct water sample collection and on-site separation of arsenic species by flowing a measured volume of water sample through the filter and cartridges connected in serial. A particular advantage of this approach is to maintain the integrity of original arsenic species in the sample. It overcomes the common problem of instability of arsenic species after water sampling and during sample storage and handling. Applications of the method are demonstrated to the speciation of arsenic in well water, raw (untreated) river water, bottled water, and a standard reference material (SRM 1643d). Results agree well with the certified values of the SRM.