SPECIATION OF MERCURY IN FISH SAMPLES BY SOLVENT-EXTRACTION, METHYL-MERCURY REDUCTION DIRECTLY IN THE ORGANIC MEDIUM AND COLD VAPOR ATOMIC-ABSORPTION SPECTROMETRY

The extraction of CH3Hg+ as bromide from fish samples by chloroform an d its direct determination in an organic medium by cold vapour atomic absorption spectrometry (CVAAS) is proposed. Parameters studied includ e the nature and concentration of the reductant and the acid stirring time. No matrix effect was observed. Inorganic Hg was determined in th e residual aqueous phase by reduction with NaBH4. Spiking studies show ed good recoveries of 102 +/- 2%. The procedure was applied to fish sa mples and the ratio between Hg as CH3Hg+ and total Hg was in the range 88-98%, usually found in the literature. The sum of the organic and i norganic Hg concentrations matched the total Hg value found by CVAAS a fter acid digestion. The detection limit (3sigma) for the total analyt ical procedure was 25 ng of Hg (as CH3Hg+) per gram of wet sample. The proposed procedure was also applied to two proficiency testing materi als and to a standard reference material and the summation of organic and inorganic Hg concentration values were in good agreement with the reference values, according to a student t test for a significance lev el of 99%, n = 5..