Chemical Analysis Using Microwave Irradiation
© G. Whittaker, 1994 & 2007. This work, or extracts from this work may be reproduced only with the written permission of the author.
The field of chemical analysis has so incorporated the use of microwave dielectric heating over recent years that a wide range of commercially available systems are now available for the analytical laboratory. 70 Many of the techniques which were originally designed for analytical use have been used, or have been adapted for use, in synthetic laboratories, and it instructive briefly to review its development. The scale of its use in chemical analysis is such that there are literally hundreds of papers describing a variety of procedures. For more detailed discussions of the subject, a range of reviews and books have been published,71-78, and it is recommended that anyone interested in this subject consults these.
The range of samples for which microwave sample preparation has been applied is vast, and includes biological materials such as food,79 blood,80 and plant and animal tissues,81,82 geological samples such as soil,83 rocks84 and sediments,85 environmental waste, 86 and even metallic materials.87
The chemical treatment of samples in preparation for instrumental analysis is often the rate limiting step for work in the analytical laboratory. The use of microwaves in sample preparation has produced dramatic time savings here as it has in the synthetic laboratory. Although microwave ovens often operate at higher powers than stirrer hotplates, this time saving more than compensates for this, and results in reduced energy demands. 88 The use of high pressure digestion bombs made from inert materials (PTFE, etc.) allows rapid digestion of samples, together with total containment, thus reducing the potential damage and dangers from corrosive acid vapours, particularly HF.
On-line89 and continuous flow systems for microwave sample preparation are available, and represent another advantage of their use, particularly as the use of high pressures are not prohibited.26 The clean and rapid nature of microwave digestion also enables complete automation of the analysis procedure, thus freeing the analyst for less routine work.90
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