Determination of mercury in coal by isotope dilution cold-vapor generation inductively coupled plasma mass spectrometry.
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.
Long
Stephen E
SE
Analytical Chemistry Division, National Institute of Standards and Technology, Gaithersburg, Maryland 20899, USA. selong@nist.gov
Kelly
W Robert
WR
D003031:Coal / Q000032:analysis*; D015386:Hazardous Substances / Q000032:analysis*; D013058:Mass Spectrometry / Q000295:instrumentation / Q000379:methods / Q000592:standards; D008628:Mercury / Q000032:analysis*; D008629:Mercury Isotopes / Q000032:analysis; D008722:Methods; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity
D003031:Coal; D015386:Hazardous Substances; D008629:Mercury Isotopes; D008628:Mercury