Analysis of mercury and methyl mercury in waters and sediments


Methyl mercury in sediments was prepared by acid bromide/methyl chloride extraction and analyzed by aqueous phase ethylation, isothermal GC separation, and cold vapor atomic fluorescence (CVAFS) detection using modified EPA draft method 1630. Total mercury in sediments was prepared by cold aqua regia digestion and analyzed by SnCl2 reduction, dual gold amalgamation, and CVAFS detection using modified EPA method 1631.

Modified EPA method 1631 was used for water analysis. Total mercury was determined by BrCl oxidation, SnCL2 reduction, and dual gold amalgamation. All mercury analysis for water samples was performed using CVAFS (Bloom, Crecelius, and Fitzgerald, 1988). Monomethyl mercury (MMHg) was liberated from water through distillation using an all teflon distillation system (Horvat, Bloom, and Liang, 1993).

Distilled samples were analyzed using aqueous phase ethylation purging onto Carbotrap, isothermal GC separation, and CVAFS (Bloom, 1989). To address accuracy and precision, all laboratory analyses followed quality assurance measures with the following minimum frequency: the collection of laboratory duplicates (one per ten samples), method blanks (three per analytical batch), filtration blank (one per ten samples), and laboratory-spike recovery (one per ten samples) or standard reference material (one per ten samples).

Mercury analytical procedures were carried out at Frontier Geosciences. All handling of samples in the laboratory was undertaken in a mercury-free clean air bench. Ultra-clean mercury trace metal protocol was used including the use of rigorously cleaned and tested teflon equipment and sample bottles and pre-screened and laboratory purified reagents. A class-100 clean air station was used and monitored routinely for low levels of total gaseous mercury. Laboratory atmosphere and water supply were also routinely monitored for low levels of mercury. Primary standards used in the laboratory were NIST certified or traceable to NIST certified materials. MMHg standards made from pure powder and calibrated for MMHg against NBS-3133 and cross verified by daily analysis of NRCC DORM-2.

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