Flow Injection Microwave-assisted Dissolution of Silicate Rocks for Magnesium Determination by Flame Atomic Absorption Spectrometry

Abstract

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 and 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 µl volume of the digested sample slurry was introduced into 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 were 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 µg ml^–1 Mg, an RSD of 0.82% (n=5) and a detection limit of 60 ng ml^–1. Reference rock samples were analysed and the results obtained agreed with the certified values.

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