Determination of Mercury in Biological Matrices

The problem you are experiencing may not be with Hg as methyl mercury. The nitric acid microwave digestion should destroy all of the methyl mercury and oxidize the Hg to the +2 valence state. Microwave digestions using nitric acid destroy most organic compounds, except aromatic ring structures. For example, no significant amounts of carbohydrates, proteins, or fatty acids have been reported in the literature when using high-pressure liquid chromatography to analyze microwave / nitric acid / digestates of organic samples.

We have found that Hg(+2) at ppb levels in acidic media adsorbs onto plastic containers. Significant loss has been observed within just a few hours of preparation. Low level (ppb) Hg solutions are stable for several days in 5-10% nitric acid solutions using borosilicate glass containers. It is NOT advisable to use plastic containers — even as autosampler containers — for the measurement (assuming an autosampler is used). If you keep the sample digestate away from plastic by using borosilicate glass containers only, you stand a better chance of obtaining good Hg recoveries.

Let me know if you need further help.

Serving you in chemistry,
Paul R. Gaines, Ph.D.
CEO of Inorganic Ventures

DISCLAIMER: Advice offered by the chemists at Inorganic Ventures is intended for the individual posing the question.