Recent trends in trace element determination and speciation using inductively coupled plasma mass spectrometry |
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Authors: | F Vanhaecke and Luc Moens |
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Institution: | (1) Laboratory of Analytical Chemistry, Ghent University, Institute for Nuclear Sciences, Proeftuinstraat 86, B-9000 Ghent, Belgium, BE |
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Abstract: | 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 technique for trace and ultra-trace
element determination, with a few thousand of instruments used worldwide. Despite this immense success, it should be realized
that in its ’standard configuration’– i.e. equipped with a pneumatic nebulizer for sample introduction and with a quadrupole
filter – ICPMS also shows a number of important limitations and disadvantages: (i) the occurrence of spectral interferences
may hamper accurate trace element determination, (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 overcome the aforementioned limitations to the largest possible extent. The application of a double focusing sector
field mass spectrometer in ICPMS instrumentation offers a higher mass resolution, such that spectral overlap can be avoided
to an important extent. Additionally, in a sector field instrument, photons are efficiently eliminated from the ion beam,
resulting in very low background intensities, making it also very well-suited for extreme trace analysis. Also the combination
of the ICP as an ion source and a quadrupole filter operated in a so-called ‘alternate’ stability region, an ion trap or a
Fourier transform ion cyclotron resonance mass spectrometer allows high(er) mass resolution to be obtained. With modern quadrupole-based
instruments, 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 sample introduction permits
direct analysis of solid samples with sufficient accuracy for many purposes. The application range of LA-ICPMS has become
very wide and the introduction of UV lasers has led to an improved spatial resolution. Solid sampling ETV-ICPMS on the other
hand can be used for some specific 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 the use of a time-of-flight (TOF) ICPMS instrument. Finally, when combined with a powerful chromatographic separation technique,
an ICP-mass spectrometer can be used as a highly sensitive, element-specific multi-element detector in elemental speciation
studies. Especially liquid (HPLC-ICPMS) and – to a lesser extent – gas (GC-ICPMS) chromatography have already been widely
used in combination with ICPMS. In speciation work, sample preparation is often observed to be troublesome and this aspect
is presently receiving considerable attention. For GC-ICPMS, new sample pretreatment approaches, such as headspace solid phase
microextraction (headspace SPME) and the purge-and-trap technique have been introduced. Also supercritical fluid chromatography
(SFC) and capillary electrophoresis (CE) show potential to be of use in combination 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-life applications reported in the literature.
Received: 30 November 1998 / Revised: 22 March 1999 / Accepted: 24 March 1999 |
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