Accurate Determination of Trace Gallium in Geological Samples by Inductively Coupled Plasma-Mass Spectrometry

There are two problems in the quantitative analysis of trace gallium in geological samples by using Inductively Coupled Plasma-Mass Spectrometry (ICP-MS). Firstly, the usual advantages of having two kinds of digestion methods are irrelevant here because sealed digestion is not appropriate for batch processing samples and an open-system digestion process is a complex procedure. Secondly, the selection of ⁶⁹Ga or ⁷¹Ga and the related interference correction are the main factors leading to low precision. The method based on the characteristic of low content organic matter in normal geology samples and requirements for ICP-MS measurement is improved on and discussed. The four-acid digestion system of HF-HCl-HNO₃-HClO₄ was conducted to dissolve the samples in a semi-hermetic environment. Adjustment of the heating temperature, acid amounts and ratios can speed up the reaction. The samples with low content organic matter are digested completely in the strong acids solution without ashing. ⁷¹Ga with an abundance of 39.9% and an empirical coefficient of 0.005 was selected. The interference of ⁵⁵Mn¹⁶O interference on the ⁷¹Ga peak was corrected by ⁵⁵Mn¹⁸O. The accuracy and precision of gallium is within 3%, and the detection limit is 0.06 μg/g. The improved method simplifies the chemical procedure and reduces the cost which is advantageous for batch processing. Moreover, this method is also suitable for other trace elements and rare earth elements.