determination of mercury in coal by isotope dilution coldvapor generation inductively coupled plasma mass spectrometry a method based on isotope dilution coldvapor inductively coupled plasma mass spectrometry idcvicpms has been developed for highaccuracy determinations of mercury in bituminous and subbituminous coals a closedsystem 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 highpurity quartzdistilled water and the mercury is released as a vapor by reduction with tinii chloride measurements of 201hg202hg isotope ratios are made using a quadrupole icpms system in timeresolved analysis mode the new method has some significant advantages over existing methods the instrument detection limit is less than 1 pgml 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 pgg memory effects are very low the relative reproducibility of the analytical measurements is approximately 05 for mercury concentrations in the range 10150 ngg the method has been used to measure mercury concentrations in six coal reference materials srm 1632b 774 ngg srm 1632c 943 ngg bcr 40 4332 ngg bcr 180 1250 ngg bcr 181 1358 ngg and sarm 20 2526 ngg as well as a coal fly ash srm 1633b 1431 ngg the method is equally applicable to other types of fossil fuels including both crude and refined oils