Recent trends in trace element determination and speciation using inductively coupled plasma mass spectrometry

During the past decade, inductively coupled plasma mass spectrometry (ICPMS ) has evolved from a delicate research tool, intended for the well-trained scientist only, into a more robust and well-established analytical techniqu e for trace and ultra-trace element determination, with a few thousand of i nstruments used worldwide. Despite this immense success, it should be reali zed that in its 'standard configuration' - i.e. equipped with a pneumatic n ebulizer for sample introduction and with a quadrupole filter - ICPMS also shows a number of important limitations and disadvantages: (i) the occurren ce of spectral interferences may hamper accurate trace element determinatio n, (ii) solid samples have to be taken into solution prior to analysis and (iii) no information on the 'chemical form' in which an element appears can be obtained. Self-evidently, efforts have been and still are made to overc ome the aforementioned limitations to the largest possible extent. The appl ication of a double focusing sector field mass spectrometer in ICPMS instru mentation offers a higher mass resolution, such that spectral overlap can b e avoided to an important extent. Additionally, in a sector field instrumen t, photons are efficiently eliminated from the ion beam, resulting in very low background intensities, making it also very well-suited for extreme tra ce analysis. Also the combination of the ICP as an ion source and a quadrup ole filter operated in a so-called 'alternate' stability region, an ion tra p or a Fourier transform ion cyclotron resonance mass spectrometer allows h igh(er) mass resolution to be obtained. With modern quadrupole-based instru ments, important types of spectral interferences can be avoided by working under 'cool plasma' conditions or by applying a collision cell. The use of electrothermal vaporization (ETV) or especially laser ablation (LA) for sam ple introduction permits direct analysis of solid samples with sufficient a ccuracy for many purposes. The application range of LA-ICPMS has become ver y wide and the introduction of UV lasers has led to an improved spatial res olution. Solid sampling ETV-ICPMS on the other hand can be used for some sp ecific applications only, but accurate calibration is more straightforward than with LA-ICPMS. Limited multi-element capabilities, resulting from the transient signals observed with ETV or single shot LA, can be avoided by th e use of a time-of-flight (TOF) ICPMS instrument. Finally, when combined wi th a powerful chromatographic separation technique, an ICP-mass spectromete r can be used as a highly sensitive, element-specific multi-element detecto r in elemental speciation studies. Especially liquid (HPLC-ICPMS) and - to a lesser extent - gas (GC-ICPMS) chromatography have already been widely us ed in combination with ICPMS. In speciation work, sample preparation is oft en observed to be troublesome and this aspect is presently receiving consid erable attention. For GC-ICPMS, new sample pretreatment approaches, such as headspace solid phase microextraction (headspace SPME) and the purge-and-t rap technique have been introduced. Also supercritical fluid chromatography (SFC) and capillary electrophoresis (CE) show potential to be of use in co mbination with ICPMS, but so far the application ranges of SFC-ICPMS and CE -ICPMS are rather limited. It is the aim of the present paper to concisely discuss the aforementioned recent 'trends' in ICPMS, using selected real-li fe applications reported in the literature.