Acid digestion of marine samples for trace element analysis using microwave heating

Abstract

A commercial laboratory microwave-acid digestion system employing two types of closed vessel, (A) completely closed and (B) pressure-relief type, was evaluated for use in sample decomposition prior to the determination of trace elements in marine biological tissue and sediment samples. The decomposition procedure consists in acid digestion in Teflon PFA vessels (with an HNO₃-HClO₄ mixture for marine biological tissues and an HNO₃-HF-HClO₄ mixture for marine sediments) using microwave heating. Subsequent evaporation on a hot-plate was undertaken with the sediment material. The resulting solutions are analysed by flame and graphite furnace atomic absorption spectrometry and by inductively coupled plasma atomic emission spectrometry. Both vessels provide rapid and almost equally satisfactory results for sample dissolution and analysis. Vessel A was judged to be more convenient whereas vessel B is likely to be safer. The sample preparation time was approximately 30 min for the marine biological tissue and 3–4 h for the marine sediment samples (including subsequent evaporation time on a hot-plate following a 30-min microwave digestion).