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 medium (HF + HNO3). A 50 mg portion of the powdered rocks was dispersed with 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 introduced to an aqueous carrier stream and mixed with a reagent stream containing boric acid before introduction into the AAS system. Chemical variables were studied and the best conditions mere obtained with 4 M HF + 1 M HNO3. Magnesium was selected as a test element, The developed procedure enables-about ten samples to be analysed per hour (including sample 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 agreed with the certified values.