Elemental mass spectrometry for quantitative proteomics

In the last decade mass-spectrometry-based proteomics has become an indispensable analytical tool for molecular biology, cellular biology and, lately, for the emerging systems biology. This review summarises the evolution and great potential of analytical methods based on elemental mass-spectrometric detection for quantitative proteomic analysis.     

Elemental analysis of high-purity solids by mass spectrometry

The applications of mass spectrometry in the determination of trace elements in some of the high-purity solid materials used in modern technology are reviewed.     

Elemental fractionation in laser ablation inductively coupled plasma mass spectrometry

The major challenge to the use of laser ablation sample introduction, combined with inductively coupled plasma mass spectrometry, is the problem of calibration. In the geological analysis of minerals, calibration is complicated by the extraordinarily wide variety of sample matrices which may be encountered. While there is a lack of mineral standards with well characterized concentrations near 1 g/g, the NIST glass reference materials (SRM 610–617) have been demonstrated to be very useful for the analysis of a wide variety of lithophile elements in silicate samples. An internal reference element, for which the concentration is known in the sample, has been widely used to make corrections for the multiplicative effects of volume (or weight) of the sample ablated, instrument drift, and matrix effects. This procedure works extremely well where elements being determined and the internal reference element being used share similar ablation behaviours; i.e., they do not fractionate progressively during the ablation and transport process. In this study, it is demonstrated that, in terms of ablation behaviour, elements fall into several distinct clusters and that the elements within these clusters correlate well with each other during a period of ablation. Thus, elements within a cluster can be determined using an internal reference element from within the same cluster. While a combination of periodic varying properties typifies the clusters, the geochemical classification of elements into lithophile (silicate loving), and chalcophile (sulphide loving) appears to offer the best characterization of the major groups.     

Elemental fractionation in laser ablation inductively coupled plasma mass spectrometry

The major challenge to the use of laser ablation sample introduction, combined with inductively coupled plasma mass spectrometry, is the problem of calibration. In the geological analysis of minerals, calibration is complicated by the extraordinarily wide variety of sample matrices which may be encountered. While there is a lack of mineral standards with well characterized concentrations near 1 microg/g, the NIST glass reference materials (SRM 610-617) have been demonstrated to be very useful for the analysis of a wide variety of lithophile elements in silicate samples. An internal reference element, for which the concentration is known in the sample, has been widely used to make corrections for the multiplicative effects of volume (or weight) of the sample ablated, instrument drift, and matrix effects. This procedure works extremely well where elements being determined and the internal reference element being used share similar ablation behaviours; i.e., they do not fractionate progressively during the ablation and transport process. In this study, it is demonstrated that, in terms of ablation behaviour, elements fall into several distinct clusters and that the elements within these clusters correlate well with each other during a period of ablation. Thus, elements within a cluster can be determined using an internal reference element from within the same cluster. While a combination of periodic varying properties typifies the clusters, the geochemical classification of elements into lithophile (silicate loving), and chalcophile (sulphide loving) appears to offer the best characterization of the major groups.     

Elemental speciation by chromatographic separation with inductively coupled plasma mass spectrometry detection

Separation techniques coupled to inductively coupled plasma mass spectrometry (ICP-MS) is reviewed. ICP-MS technique is described briefly. Coupling of the different separation techniques are described, together with the most common applications used for each technique that has been described in the literature. An overview for the future of separation techniques coupled to ICP-MS with regard to elemental speciation is discussed.     

Elemental speciation by liquid chromatography-inductively coupled plasma mass spectrometry with direct injection nebulization.

A new version of the direct injection nebulizer (DIN) is used to interface liquid chromatographic (LC) separations with element-selective detection using inductively coupled plasma mass spectrometry (ICP-MS). The DIN injects all of the sample into the ICP and has a dead volume of less than 1 microliter. Charged species of arsenic and tin are separated as ion pairs on a micro-scale (1 mm i.d.), packed, reversed-phase column. Detection limits are 0.2-0.6 pg for arsenic and 8-10 pg for tin. For methanol + water eluents, the signal is highest at 25% methanol and stays within 25% of this maximum as the methanol fraction is varied from 20 to 80%. Compared with LC-ICP-MS with conventional nebulizers, the absolute detection limits and chromatographic resolution are substantially superior, and the dependence of analyte signal on solvent composition is somewhat less severe with the DIN.     

Elemental sulfur as a versatile low-mass-range calibration standard for laser desorption ionization mass spectrometry

Facile generation of series of singly charged radical anions (S _n ^−· ; n=1–15) and cations (S _n ^+· ; n=2–11) by direct laser ionization renders elemental sulfur an excellent material for the low-mass-region calibration of time of flight (TOF) mass spectrometers. Upon irradiation by a 337-nm UV laser, elemental sulfur undergoes facile ionization without the need of an additional laser-absorbing matrix. An intense and evenly spaced set of peaks is obtained in both modes.     

Elemental ratio determinations and compound-independent calibration using microsecond pulsed glow discharge time-of-flight mass spectrometry

A new prototype based on a microsecond pulsed glow discharge ion source coupled to a time-of-flight mass spectrometer was recently designed, constructed and analytically evaluated in our laboratory for simultaneous collection of elemental and molecular information, and as a gas-chromatographic detector of compounds of environmental concern. To investigate further the analytical capabilities of such a new setup, its capability for the determination of element ratios in volatile organic halogenated compounds has been explored. Moreover, compound-independent calibration has been carried out with the prototype as well. The results demonstrated that the intensity ratios (analyte to internal standard) were linear with the corresponding ratio of concentrations. Both for chlorine and bromine (measured in the prepeak) and for BrC (measured in the plateau) the slope was 1 and the intercept was 0. Moreover, detection limits were improved by more than 1 order of magnitude as compared with using external calibration. The applicability of the proposed approach has been demonstrated for the straightforward determination of chloroform in drinking and river waters.     

Elemental analysis of freshwater samples collected in the former USSR by inductively coupled plasma mass spectrometry

Approximately 100 freshwater samples (ground water, surface water, etc.) collected in the former USSR were analyzed by inductively coupled plasma mass spectrometry (ICP-MS). Standard water, NBS SRM 1643b, was used for quality control. By using the semi-quantitative analysis mode, analytical data and certified values (or informative values) were in agreement within ±30%. Concentrations of B, Ni, Se, Sr and Ba were found to be higher than global means. Concentration levels of Ag and Pb tended to be lower. For Be, V, Cr, Mn, Co, Cu, Zn, As, Mo, Cd, Tl, and Bi, the concentrations were almost equal to the global levels.     

A double quadrupole for mass spectrometry/mass spectrometry

A double quadrupole mass spectrometer has been constructed to study unimolecular and collision-induced dissociation products from mass-selected ions. The two quadrupoles are closely coupled and the dissociation products sampled from a 2.5-mm interquadrupole region. Spectra obtained on the double quadrupole instrument are compared with published data obtained with triple quadrupole and reversed-sector (MIKE) mass spectrometers. The results indicate that the simple double quadrupole spectrometer is a highly efficient device which is a viable alternative to more complex quadrupole or sector instruments for obtaining dissociation spectra of mass-selected ions.     

Elemental labelling combined with liquid chromatography inductively coupled plasma mass spectrometry for quantification of biomolecules: A review

This article reviews novel quantification concepts where elemental labelling is combined with flow injection inductively coupled plasma mass spectrometry (FI-ICP-MS) or liquid chromatography inductively coupled plasma mass spectrometry (LC–ICP-MS), and employed for quantification of biomolecules such as proteins, peptides and related molecules in challenging sample matrices. In the first sections an overview on general aspects of biomolecule quantification, as well as of labelling will be presented emphasizing the potential, which lies in such methodological approaches. In this context, ICP-MS as detector provides high sensitivity, selectivity and robustness in biological samples and offers the capability for multiplexing and isotope dilution mass spectrometry (IDMS). Fundamental methodology of elemental labelling will be highlighted and analytical, as well as biomedical applications will be presented. A special focus will lie on established applications underlining benefits and bottlenecks of such approaches for the implementation in real life analysis. Key research made in this field will be summarized and a perspective for future developments including sophisticated and innovative applications will given.