A speciation scheme for ultratrace levels of mercury is described in which inorganic and organomercury are selectively reduced by SnCI, and NaBH,, respectlvely. The volatilized elemenltal Hg is determined by cold vapor atomic absorption. The detection limits for inorganic and organomercury species are in the 0.003-0.005 ppb range and both types of mercury can be determined in a I-mL sample In about 3 mln. The procedure is used to determlne the chemlcal forms of Hg In water, tuna, hair, and urine samples. Preservatlon condltlons typically used lor storage of inorganic Hg solutions are shown to cause decomposition of methylmercury.

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