Automated Microwave Flow Digestion

The microwave-assisted flow digestion system called AutoFlow is used at pressure levels up to 60 bar and temperatures up to 250° C to perform on-line digestion of organic samples. The slurry of organic samples is pumped through a coil of 8 m Teflon tubing located in a microwave field. Due to the high temperature an effective oxydation of the organic matrix with half concentrated nitric acid is obtained. The Teflon tubes withstand the high pressure level at 250°C because of a patented sophisticated pressure equilibration technique. The residence time of the digestion mixture in the microwave field is controlled by the flow rate of a HPLC pump. 2-3 minutes is enough for a suitable oxydation efficiency. The sample can be either a liquid or a 3 % slurry of solid organic materials in half concentrated nitric acid. Food slurries are prepared by pre mixing in a Büchi-Mixer and final mixing in an Ultradurax. For online element determination ICP-OES or ICP-MS is used.