Inorganic Mass Spectrometry
In the course of its about one hundred years of development, mass spectrometry has not only been able to contribute towards obtaining important findings about the structure of atomic nuclei, the isotopy of the elements and the exact isotopic masses, but it has developed into a leading analytical method in the field of inorganic analysis for high-tech research and routine applications in a variety of modern application fields (e.g. materials science for the characterization of high-purity metals, semiconductors and insulators, microelectronics, metallurgy, geology and mineralogy, environmental analysis and medicine).
In the past decade, inorganic mass spectrometry has experienced an exemplary development, in particular, due to the extended application of plasma ionization and has thus established itself as a universal high-performance method of trace, ultratrace and precision isotope analysis. Applications of the methods of inorganic mass spectrometry (SSMS, GDMS, LIMS, TIMS, RIMS, SIMS, SNMS, ICP-MS and LA-ICP-MS) comprise the analysis of gaseous, liquid and solid sample materials.
It is thus possible today to carry out ultratrace analyses of extremely small sample quantities (µl to nl sample volumes) down to the sub-fg/ml concentration range in aqueous solutions and precision isotope analyses by ICP-MS. Especially on-line coupling techniques (HPLC-ICP-MS, CE-ICP-MS) for the separation of isobaric interferences and for the determination of element species are becoming increasingly important. The classical methods of direct solid-state analysis are replaced by efficient and fast methods for the analysis of conducting and nonconducting solid samples, e.g. by LA-ICP-MS.
In the past few years, a remarkable further development of inorganic mass spectrometry has taken place primarily in the field of inductively coupled plasma source mass spectrometry (ICP-MS). Proven mass-spectrometric methods such as spark source mass spectrometry (SSMS), laser ionization mass spectrometry (LIMS) and glow discharge mass spectrometry (GDMS) have either been completely replaced for the trace analysis of solids or only occupy special "niches" in inorganic mass spectrometry. Such a development can also be observed in the field of precise isotope analysis, where the ICP-MS methods (especially sector-field instruments with multiple collectors) reach an efficiency which otherwise is only achieved by thermal ionization mass spectrometry (TIMS) with multiple collectors. Nowadays, isotope analyses of aqueous solutions are possible by multicollector ICP-MS with a precision of 0.002 % and better.
One of the essential advantages of ICP-MS is that it can be easily coupled to a large variety of sample introduction systems and separation and enrichment methods for liquid samples (e.g. to HPLC and CE). The results thus obtained with respect to high selectivity, sensitivity and small sample volumes are as remarkable as the successes of ICP-MS with the newly developed sample introduction systems (various high-efficiency nebulizer systems for aqueous solutions or laser ablation for direct trace and isotope analyses of solid samples). Another essential step was the commercial introduction of ICP-MS instruments with gas collision cells for partially reducing or suppressing the interference effects in the mass spectra. As early as 1982/83 J.S. Becker and H.-J. Dietze were concerned with the fundamentals and application of collision cells to increase sensitivity in inorganic mass spectrometry. At that time, a gas target for charge-exchange processes was applied in an ultrasensitive mass spectrometer with laser ion source.
In modern ICP mass spectrometers with collision cell, selective chemical reactions with collision gases lead to an increase in transmission and, consequently, an increase in sensitivity, to the dissociation of disturbing molecular ions and reduction of the background. All these novel developments in inorganic mass spectrometry have been taken into account by the research and development strategies at ZEA-3 and their applications in the ZEA-3 analytical service for the institutes of Research Centre Jülich.