DETERMINATION OF METHYLMERCURY IN NATURAL-WATER SAMPLES BY STEAM DISTILLATION AND GAS-CHROMATOGRAPHY ATOMIC FLUORESCENCE SPECTROMETRY

Steam distillation was evaluated as a technique for the separation of methylmercury from natural water samples prior to quantification by GC -atomic fluorescence spectrometry. Recoveries of methylmercury chlorid e spikes ranged from similar to 100% in a wide variety of natural fres hwater and estuarine samples to 80% in seawater. The addition of ammon ium pyrrolidine dithiocarbamate (APDC) was found to improve the recove ry of methylmercury chloride spikes in MilliQ water from 73 to 89% and in seawater from 80 to 85%. Codistillation of inorganic mercury was e liminated by addition of APDC to the samples. Precision in MilliQ wate r was 2.0% RSD at 0.2 ng L-1 CH3HgCl (n = 10) and 1.6% RSD at 2.0 ng L -1 CH3HgCl (n = 10). The limit of detection for the method was 0.024 n g.L-1 (3 sigma) for a 50 mL sample. The steam distillation procedure w as tested for and found free of measurable artifactual formation of me thylmercury. The method was compared to nitrogen-assisted distillation and found to give comparable results with the added advantage of hand ling sample sizes up to 100 mL. Compared to previously employed separa tion procedures, steam distillation offers the advantages of robustnes s and a considerably increased sample throughput (at least four sample s per hour) without any compromise in analytical performance.