Mercury sampling/analysis difficulties

The programme to improve the quality of MeHg determinations started in 1987 with a consultation of European experts. From the beginning it was clear that it was essential to examine critically each step of the methods used in mercury speciation analysis. As described below, a series of exercises of increasing difficulty were designed and interlaboratory studies were conducted in 1987-88 (first round-robin with simple solutions), 1988-89 (cleaned and raw extracts) and 1989-90 (extracts and real samples). The certification of... 

The most obvious sources of error in analyses are related to insufficient extraction, low and irreproducible recoveries, insufficient peak resolution in chromatography, and the transformation of mercury species that may lead to artifacts. In the case of solubilized samples such as fish and mussels, speciation analysis was generally successful. However, with solids, techniques to remove or solubilize MeHg are complicated to validate by using spiking or tracer approaches, as it is difficult to prove that complete extrac-tion/separation has been achieved. A classical example of this difficulty is speciation of MeHg in sediments and soils. The only feasible approach adopted in certification of MeHg is to use different analytical approaches - that is, various extraction/sep-aration schemes and detection methods... 

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