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 (NH 4 F 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, NH 3 released from the decomposition of molten NH 4 F can effectively prevent the loss of halogens released from geological samples. Chlorine, Br and I were not lost during NH 4 F digestion at 220 °C for 0.25-6 h. The limits of quantitation for NH 4 F 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 NH 4 F digestion were in agreement with their certified values, confirming that the high-performance rapid bulk rock NH 4 F 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 HNO 3 + HF digestion could effectively extract Br and I from soil and sediment samples, and that HNO 3 acid digestion is only suitable to use for the determination of Br and I in soil samples.

Atomic spectrometry update – a review of advances in environmental analysis

“…Electrothermal digestion with powdered NH 4 F was proposed 114 for the determination of the halogens Br, Cl and I in soils and sediments. During the high-temperature digestion (optimised conditions: 220 °C, 2 h, 400 mg NH 4 F, for 50 mg soil or 100 mg powdered rock/sediment samples), NH 3 released from the decomposition of molten NH 4 F prevented loss of the sample halogens, which were leached from the resultant solid residue with 5% (v/v) aqueous ammonia.…”

“…The analysis of Ti-rich materials using the two digestion methods gave ICP-MS datasets for 36 trace elements that were within ±10% for most elements. The one exception was rutile, for which the closed-vessel acid digestion suffered from the formation of an insoluble precipitate that caused low recoveries of Nb, Ta, Ti and V. He et al 114 employed NH 4 F digestions in the determination of Br, Cl and I in geological materials by SF-ICP-MS. Ammonia released from the decomposition of molten NH 4 F at 200–240 °C in a screw-top PFA vial was effective in preventing the loss of halogens released from geological samples. Analysis of a range of RMs confirmed that the method was capable of extracting Br, Cl and I quantitatively from rocks, sediments and soils, with LOQs of 0.018, 2.8 and 0.003 μg g −1 , respectively.…”