Gas chromatography-microwave-induced plasma mass spectrometry (GC-MIP-MS): a multi-element analytical tool for organic geochemistry

Direct interfacing of a high temperature capillary gas chromatograph with a high power microwave-induced plasma (MIP) torch and quadrupole mass spectrometer, produces a GC-MIP-MS instrument capable of providing information about the elemental compositions of a wide range of organic geochemical analytes. Preliminary experiments show that at least carbon, each of the halogens (F, Cl, Br, I), phosphorus, sulphur and many transition elements can be determined quantitatively by GC-MIP-mass chromatography of the elemental masses (e.g. for carbon, m/z 12). Linearit of response (1–250 μg ml−1 chlorotetradecane as 37Cl, r = 0.999) and limits of detection (ca. 1 ng on-column for Cl) appear to be compatible with many organic geochemical requirements, judging from these early studies, but selectivity of the various elemental masses has yet to be investigated. Isobaric interferences experienced with the use of helium as a plasma gas are fewer and different from those encountered with argon inductively-coupled plasmas (ICP), allowing a different and wider range of elements to be determined. For example, the use of a high power (up to 1500 W) helium MIP provides a plasma which is capable of ionising elements such as arsenic and selenium, which are only poorly ionised by ICP ion sources. Furthermore, unlike lower power MIPs, the high power plasma is stable even when liquids are introduced, suggesting that the future development of LC-ICP-MS should be possible, thereby further extending the range of organic geochemical analytes that can be determined and allowing a better quantitative understanding of heterogeneous, multielemental organic matter.