Open microwave-assisted digestion

The common methods used for dissolving samples for metals analysis are digestion in an open flask, digestion in a pressurized, sealed container, and microwave assisted decomposition. Some common solvents used are listed in Table 5.1. 

Microwave assisted wet digestion has attracted considerable attention and has been successfully applied to plant material. Both open and closed vessels have been used, but the most popular approach is the sealed bomb method (Kingston and Jassie, 1988 Sulcek and Povondra, 1989 Matusiewicz, 1991). Karanassios et al. (1991) describe microwave stopped flow digestion systems that can give rapid (ie, less than 5 min) reproducible extractions of elements of environmental concern from plant samples. 

Many different designs for microwave-assisted flow digestion systems have been published [25, 32, 101], which open up new possibilities, primarily in fully automated sample preparation for elemental analysis. 

Dynamic systems for high-pressure microwave treatment were developed much later than open-vessel systems. Operating under a high pressure reduces the flexibility afforded by working at atmospheric pressure. However, some recently developed devices allow microwave-assisted high-pressure digestion and extraction in a dynamic manner [33,34]. 

Magnesium, calcium, iron Foodstuffs Microwave-assisted sample digestion with concentrated nitric acid UV-Vis 5.0- 50.0 mg L 15.0- 150 mg L 2.0- 20.0 mg L 1 Sequential injection system direct [432] sample introduction as a natural suspension or as a slurry open digestion vessel inside a microwave oven... 

Digestion of soil samples for analytical purposes can be carried out in closed vessels (usually assisted by a microwave oven) or open crucibles (either as acid digestion or with a flux—mixture of salts—to open out the minerals). The details vary considerably and depend on the type of soil, the availability of proper equipment, and the analytical technique that will subsequently be used for the measurement, as demonstrated by the examples discussed later. After discussing some specific examples, we will try to derive the general guidelines and insights for the treatment of soil samples for the determination of the uranium content. 

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