DETERMINATION OF ATMOSPHERIC HG BY COLLECTION ON IODATED CARBON, ACID DIGESTION AND CVAFS DETECTION

An established industrial monitoring technique has been refined to allow the accurate determination of total gaseous Hg in air at background levels (1-3 ng . m(-3)). Samples are collected under vacuum through a commercially available iodide-impregnated carbon trap. For analysis, the trap is digested in a 7:3 (v/v) mixture of HNO3 + H2SO4, and an aliquot of the digest analyzed by SnCl2 reduction, dual gold amalgamation, and cold vapor atomic fluorescence spectrometric (CVAFS) detection. The traps exhibit little breakthrough (<5%) under flow rates of up to 1.0 1 . min(-1) for periods up to 10 days. The mean value for the blank on the half traps was found to be 0.40 +/- 0.16 ng (n=20), resulting in a 3 sigma detection limit of 0.07 ng . m(3) (1 week sample at 1.0 L . m(-3)). Replicate field collections show a between-trap RSD of +/- 6.4%, while field intercomparison with gold trapping resulted in 104 +/- 20% recovery in the 1-4 ng/m(3) concentration range.