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Serving: Arkansas, Louisiana, New Mexico, Oklahoma, Texas, and 66 Tribal Nations

A Comparison of Closed Vessel Microwave Digestion versus Conventional Digestion Procedures for Determination of Mercury in Fish Tissue by CVAA Spectrometry

David C. Stockton and Barbara Schuppener,

U.S. Environmental Protection Agency, Region 6 Lab, Houston, Texas 77099


Many digestion procedures are available for the determination of total mercury in fish tissue. Both conventional open beaker methods and microwave digestion methods have been developed and widely used in the past. Conventional open vessel, water bath methods are inexpensive to implement but time consuming, require numerous reagent additions, and provide opportunity for contamination during digestion. Microwave techniques are rapid, require fewer reagents and lessen possibilities of contamination when closed vessels are used. However, microwaves outfitted with external pressure-controlling devices are more costly to purchase. With a closed vessel utilizing an outer pressure insulator with a compressible inner disc, inner Teflon liner, lid, and o-ring, a laboratory can use a first generation laboratory microwave oven with no additional pressure controlling device to process raw fish tissue with nitric acid and 60-second digestion time. Total mercury can then be determined by cold vapor atomic absorption spectrometry with both acceptable precision and spike recovery.

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