Quantification of Cl, Br and I in Geological Materials by NH4F Digestion: Comparison with Rapid Acid Digestion

Abstract

The lack of analytical techniques for halogens in geological materials is mainly due to the loss of analytes during sample preparation. This study describes a rapid bulk rock digestion method (NH₄F digestion) for determination of the abundances of Cl, Br and I in geological materials by SF-ICP-MS. During high temperature (200–240 °C) digestion, NH₃ released from the decomposition of molten NH₄F can effectively prevent the loss of halogens released from geological samples. Chlorine, Br and I were not lost during NH₄F digestion at 220 °C for 0.25–6 h. The limits of quantitation for NH₄F digestion were 2.8, 0.018 and 0.003 μg g^-1 Cl, Br and I, respectively. Most results for halogens in geological reference materials by NH₄F digestion were in agreement with their certified values, confirming that the high-performance rapid bulk rock NH₄F digestion has sufficient digestion capability to extract Cl, Br and I from rocks, sediments and soils. In comparison, results obtained following acid digestion showed that HNO₃ + HF digestion could effectively extract Br and I from soil and sediment samples, and that HNO₃ acid digestion is only suitable to use for the determination of Br and I in soil samples.