Understanding Mercury
Friday, 27 July 2012 17:56

Introduction - Mercury has a history full of fascination and wonder. It is the only metal that is in liquid form at room temperature. The ancient alchemists considered it the original metal and used large quantities of it in their attempts at transmutation. It was used to construct reflecting pools and decorative fountains in the courtyards of kings. In modern times it has been used in thermometers, thermostats, and as parabolic mirrors in telescopes. It was with great disappointment that mankind fully understood the toxicity of such a visually fascinating element. Because of mercury’s tendency to accumulate in organisms it can have very long lasting and slow developing negative health effects. Many States now ban products containing mercury from crossing over State lines. The requirements for mercury removal are getting tighter and detection limits are falling.

Method Summary – For CVAAS an acidified portion of the sample is digested and oxidized at 95°C with permanganate and persulfate solutions. After digestion, excess permanganate is removed via the addition of hydroxylamine hydrochloride. Stannous chloride reduces the mercury to its elemental form. The mercury is then measured via cold vapor atomic absorption.

For CVAFS, the sample is oxidized with a bromine based reagent. Following oxidation, the sample is treated with hydroxylamine hydrochloride and stannous chloride in a similar manner to CVAAS. In the purge and trap method, the mercury is separated from the sample and carried in an inert gas stream, typically argon, to a series of gold traps that help to concentrate the mercury. From there it is introduced into the CVAFS detector. For CVAFS without the purge and trap, the mercury is separated from the sample and carried directly into the detector.

What You Should Know – While proper sampling and storage techniques are important in any analytical process, it is even more important in the case of mercury. With the advent of new sampling and analytical techniques in the mid 1980s, scientists discovered that the previously reported levels of mercury in the environment were biased high, sometimes by as much as three orders of magnitude. It was found that, outside of areas in which mercury was being mined, the highest concentration of the metal was to be found in and around man-made artifacts. Paints, electrical components, lighting fixtures, thermometers, thermostats, and batteries were among the common contributors to ambient contamination. Conditions were often worse in the laboratories performing the analyses due to mercury based reagents and equipment with mercury containing parts being even more prevalent. Lack of knowledge as to the true environmental amounts coupled with mercury’s volatility made unintentional contamination of the analysis unavoidable. The EPA has published method 1669 to give guidance on trace metal sampling. Strict adherence to these guidelines will minimize the amount of contamination caused by the sampling procedure.

Click here for a more detailed Lab Matters PDF on Understanding Mercury

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