Determination of Mercury in Coal by Isotope Dilution Cold-Vapor Generation Inductively Coupled Plasma Mass Spectrometry

Abstract

A method based on isotope dilution cold-vapor inductively coupled plasma mass spectrometry (ID-CV-ICPMS) has been developed for high-accuracy determinations of mercury in bituminous and sub-bituminous coals. A closed-system digestion process employing a Carius tube is used to completely oxidize the coal matrix and chemically equilibrate the mercury in the sample with a 201Hg isotopic spike. The digestates are diluted with high-purity quartz-distilled water, and the mercury is released as a vapor by reduction with tin(II) chloride. Measurements of 201Hg/202Hg isotope ratios are made using a quadrupole ICPMS system in time-resolved analysis mode. The new method has some significant advantages over existing methods. The instrument detection limit is less than 1 pg/mL. The average blank (n = 17) is 30 pg, which is roughly 1 order of magnitude lower than the equivalent microwave digestion procedure. The detection limit in coal is blank limited and is approximately 40 pg/g. Memory effects are very low. The relative reproducibility of the analytical measurements is approximately 0.5% for mercury concentrations in the range 10-150 ng/g. The method has been used to measure mercury concentrations in six coal reference materials, SRM 1632b (77.4 ng/g), SRM 1632c (94.3 ng/g), BCR 40 (433.2 ng/g), BCR 180 (125.0 ng/g), BCR 181 (135.8 ng/g), and SARM 20 (252.6 ng/g), as well as a coal fly ash, SRM 1633b (143.1 ng/g). The method is equally applicable to other types of fossil fuels including both crude and refined oils.

Evaluating the role of re-adsorption of dissolved Hg2+ during cinnabar dissolution using isotope tracer technique

“…For traditional isotope dilution methods, Hg isotope ratios in the solution are expected to be a known constant (natural abundance of Hg in most cases) [40][41][42][43][44]. However, Hg isotope ratios would change with time when investigating dynamic processes in which isotope tracers were spiked.…”

Certification of NIST Standard Reference Material 1575a pine needles and results of an international laboratory comparison

“…This sample decomposition method has been described in detail elsewhere (Long, et al, 2002) and a brief description is included here. Approximately 0.25 g of sample from each bottle was weighed into a cleaned Carius tube and spiked with a weighed aliquot of 201 Hg followed by the addition of 5 mL of high-purity HNO 3 .…”

Application of chemical vapor generation in ICP-MS: A review

“…Initially, enriched isotope was used as an ideal internal standard for the determination of elements like Cd [80], Te [81] and Tl [82] after vapor generation by ICP-MS. In 2002, Long et al [83] proposed an ID-CV-ICP-MS based method for high accuracy determination of mercury in coals. Using compromised vapor generation conditions for different elements, simultaneous determination of several vapor forming elements were realized by HG/CV-ID-ICP-MS [78].…”