Analysis of Methylated Heavy Metals 1421 Methylation Methods

Pure reference standards are a prerequisite for any qualitative or quantitative analysis of an organometallic compound in nature. However, not every organometallic substance is available commercially. For example, different chemical methods can be applied to methylate mercury. Methylmercury derivatives can be produced using HgO and tetramethyltin (Hintelmann and Evans 1997) or by using HgCl2 and MgMeCl (Snell et al. 2000). The main problem with this methylation reaction is the low yield of product. An alternative possibility for the production of methylated mercury is to use methylcobalamin, in analogy to the bacterial pathway for mercury methylation, where cobalamins are involved. The latter chemical reaction results in higher yields of methylated end-products. In addition, the conditions required for this reaction has not to be as exact as those needed for other chemical reactions.

Another example of an organometallic synthesis is the isotopic enrichment of trimethyl lead. In this case, the reaction of lead bromide with methyllithium leads to tetramethyl lead. The desired trimethyl lead iodide can then be derived by adding elementary iodine (Poperchna and Heumann 2005a,b).

The methods discussed in the following sections have also been summarised by Cornelis et al. (2003).

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