Detremination of Mercury Isotopic Profile by Inductively Coupled Plasma Mass Spectrometry: Possibilities and Limitations

A systematic study on the efficiency of inductively coupled plasma quadruple mass spectrometry (ICP–QMS) in determination of stable mercury isotopes profile has been conducted. Two types of effects have been observed: non-specific, which influenced all mercury isotopes, and specific, which applied only to selected isotopes. Non-specific effects were those, for which the sensitivity depended significantly on the type of mercury compound present in the solution: sensitivity decreased almost 2 and 3 times for chloride and phenylmercury PhHg+ ions, respectively, compared to that for mercury in the form of inorganic Hg2+ as a nitrate(V). The influence of platinum and lead was specific for isotopes exposed to isobaric spectral interferences, which meant that determination of the following isotopes: 199Hg, 200Hg, 201Hg and 202Hg was unaffected. In case of 196Hg, 198Hg and 204Hg significant isobaric interferences from 196Pt, 198Pt and 204Pb ions were detected. It has been found that commonly used mathematical correction was not always effective and depended on the concentrations of interferents in the solution. To overcome this problem, proper detection mode (pulse or analogue) for monitoring mercury and interfering ions has been proposed.