FLOW-INJECTION SYSTEMS FOR DIRECTLY COUPLING ONLINE DIGESTIONS WITH ANALYTICAL ATOMIC SPECTROMETRY .2. REACTIONS IN A MICROWAVE FIELD

A flow injection system incorporating a stopped-flow microwave-heated reactor was constructed for the preparation of solutions for subsequent analysis by atomic spectrometric techniques. Slurry samples were injected into the manifold and transported into a glass reactor mounted inside a microwave oven. Nitric acid was flushed into the reactor, which was then sealed and the contents were heated by an appropriate microwave programme so that the pressure was held at 400 lb in-2 for 5 min. During this period the presssure was continuously monitored. After cooling, the reactor was vented and the contents were flushed out into a calibrated flask and diluted to volume. The procedure was evaluated by the determination of some minor elements in cocoa powder (for which the results were compared with those of two other digestion procedures), Horse Kidney (International Atomic Energy Agency Certified Reference Material H-8) and coal [National Institute of Standards and Technology Standard Reference Material 1632b Trace Elements in Coal (Bituminous)]. A comparison of the results showed no significant difference (95% confidence) for the trace element contents of these materials between the flow injection method and other two methods of sample preparation. An analysis of variance showed no indication of sample slurry inhomogeneity. Low recoveries were obtained for the coal material, perhaps owing to incomplete dissolution of the silicate constituents.