FLOW-INJECTION MICROWAVE-ASSISTED DISSOLUTION OF SILICATE ROCKS FOR MAGNESIUM DETERMINATION BY FLAME ATOMIC-ABSORPTION SPECTROMETRY

A flow injection system based on on-line microwave-assisted digestion was tested as a tool to-perform silicate rock dissolution in acid medi um (HF + HNO3). A 50 mg portion of the powdered rocks was dispersed wi th the acid mixture add stirred for a few minutes. Using a 3.8 ml min( -1) flow rate, the sample slurry was digested inside a microwave oven for 10 s. A 20 mu l volume of the digested sample slurry was introduce d to an aqueous carrier stream and mixed with a reagent stream contain ing boric acid before introduction into the AAS system. Chemical varia bles were studied and the best conditions mere obtained with 4 M HF 1 M HNO3. Magnesium was selected as a test element, The developed proc edure enables-about ten samples to be analysed per hour (including sam ple preparation) and affords a linear dynamic range from 0.5 to 4 mu g ml(-1) Mg, an RSD of 0.82% (n=5) and a detection limit of 60 ng ml(-1 ). Reference rock samples mere analysed and the results obtained agree d with the certified values.