The digestion of a wide range of matrices, from fish to rocks, is possible in a stainless steel pressure vessel fitted with a PTFE container. It is particularly useful for demanding trace element analyses. It was first developed by Professor Tolg, the method being described by Kotz et al. (1972). Pressure vessels are expensive, but digestion times can be as little as 60 s to dissolve fish tissue in nitric acid. An article comparing closed vessel microwave digestion versus conventional digestion procedures for the determination of
Using autoanalysis, ammonium ions are reacted with sodium phenate and sodium hypochlorite to give the indophenol blue colour by the Berthelot reaction (Berthelot, 1859).
Fig. 4.1. Colorimetric reaction converting protein nitrogen to the indophenol blue colour.
mercury in fish tissue by cold vapour AAS using a basic laboratory microwave is given by D.C. Stockton and B. Schuppener at:
http:7www.epa.gov/earth1r6/6lab/mercury.htm Typical vessels are described at the following website:
http://www.berghofusa.com/berghof.htm Digestion systems are supplied by CEM Corporation in the USA:
http://www.cem.com/applctns/AcdDgst.html The UK supplier is CEM (Microwave Technology) Ltd, Unit 2 Middle Slade, Buckingham Industrial Park, Buckingham MK18 1WA, UK Tel. +44 (0) 1280 822873; Fax. +44 (0) 1280 822342. Their HP-500 Plus vessel system can handle 14 soil or plant digestions at a time.
Microwave systems are also used for accelerated Soxhlet extractions with reduced solvent consumption, and microwave muffle furnaces with air-exhaust for rapid ashing.
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