Development and complete validation of a method for the determination of dimethyl mercury in air and other media

The rigorous validation of a previously developed research method for the determination of dimethyl mercury ((CH3)2Hg) in environmental samples is presented. During atmospheric analysis, (CH3)2Hg was trapped on Carbotrap™ and analyzed by thermal desorption, isothermal GC separation, and cold vapor atomic fluorescence spectrometry (CVAFS). Water samples were analyzed after direct purging of 100 mL aliquots onto Carbotrap™, while sediment and tissue samples were digested with 10 mL of 25% KOH in methanol at 60 °C and diluted to 40 mL with methanol. An ambient air-spiking manifold, which allowed simultaneous replicate sampling, was constructed in a room controlled for temperature and humidity. (CH3)2Hg was introduced into the feed airflow (0.4 m3 min−1) from a well-calibrated diffusion cell, to obtain a concentration of approximately 5.5 ng m−3 as Hg. Samples were collected onto Carbotrap™ columns, and the total volumes quantified by integrating mass flow meters. Trapping efficiency was investigated over a range of sampler flow rates (0.05-0.25 L min−1), volumes (2-200 L), collection temperatures (15-42 °C) and relative humidity levels (10-70%). Method detection limits (MDLs), analytical precision and accuracy were quantified for all media. Carbotrap™ was found to be the best choice as a sampling media, whereas Tenax™ was found to be inadequate due to high breakthrough (>70%). This study verified that the method is sufficiently precise, accurate and robust for field sampling at mercury contaminated sites. No interferences were observed from elevated levels of potential co-contaminants, Hg0 (125 ng m−3) and H2S (1.27 ppmv).