Measurement techniques mass spectrometry applications

Most of the mass spectrometry applications for combinatorial chemistry will be described in the following sections of this chapter. Here we will give a short overview of MS techniques utilized for the characterization of resin-bound molecules. The majority of publications in this field describe applications of matrix-assisted laser desorption ionization (MALDI), combined with time-of-flight (TOF) detection. The major difference of MS application for analysis of resin-bound molecules from the above-described NMR and IR applications is that analyte should not be covalently bound to solid support prior to mass measurement. Detachment of compound molecules from resin can be done chemically (for example, by bead exposure to TFA vapors) [30,31] or photochemically, such that cleavage, desorption, and ionization of molecules occur simultaneously upon stimulation by laser radiation [32], Since the... 

Detection techniques of high sensitivity, selectivity, and ease of coupling with sample preparation procedures are of special interest for measuring PGM content in biological and environmental samples. ICP MS, electrothermal atomic absorption spectrometry (ET AAS), adsorptive voltammetry (AV), and neutron activation analysis (NAA) have fotmd the widest applications, both for direct determination of the total metal content in the examined samples and for coupling with instrumental separation techniques. Mass spectrometry coupled with techniques such as electrospray ionization (ESI) and capillary electrophoresis (CE) (e.g., ESI MS", LC ESI MS", LC ICP MS, CE MS", and CE ICP MS) offer powerful potential for speciation analysis of metals. MS is widely used for examination of the distribution of the metals in various materials (elemental analysis) and for elucidation of the... 

All the methods of analysis described above, with the exception of some of the mass spectrometry applications, measure concentrations relative to a standard of known composition or to a calibration curve, drawn on the basis of standards of known composition. The standards used in the construction of calibration curves are either ultra-pure chemical reagents or, where matrix effects are important in some rock samples, well-analysed in-house samples and international reference samples (Govindaraju, 1984 Abbey, 1989). In either case the standards should be analysed using the most precise technique possible. Qearly the accuracy of the final analysis depends upon the accuracy of the standards used in calibration and systematic effbis can easily be introduced. 

Compared with most analytical techniques, mass spectrometry is generally faster, providing both separation of complex mixtures and a fundamental measurement simultaneously. Due to this analytical speed, mass spectrometry is also amenable to high-throughput analysis of very many samples. Therefore, mass spectrometry represents an important approach for analysis of biological exposure [56]. In addition to clinical applications, diagnostics are also needed for food and water safety, bioreactor analysis/sterility assurance, and environmental microbiology. 

Ton-molecule reactions are of great interest and importance in all areas of kinetics where ions are involved in the chemistry of the system. Astrophysics, aeronomy, plasmas, and radiation chemistry are examples of such systems in which ion chemistry plays a dominant role. Mass spectrometry provides the technique of choice for studying ion-neutral reactions, and the phenomena of ion-molecule reactions are of great intrinsic interest to mass spectrometry. However, equal emphasis is deservedly placed on measuring reaction rates for application to other systems. Furthermore, the energy dependence of ion-molecule reaction rates is of fundamental importance in assessing the validity of current theories of ion-molecule reaction rates. Both the practical problem of deducing rate parameters valid for other systems and the desire to provide input to theoretical studies of ion-molecule reactions have served as stimuli for the present work. 

One of the chief reasons for the recent extensive work in this field has been the recognition that ion-molecule reactions are highly relevant to radiation chemistry. The possibility that certain simple reactions, such as the formation of H3+, participate in the mechanism of product formation was appreciated much earlier 14), but wider applicability of this concept required that the generality of such reactions be demonstrated by an independent, unequivocal method. Mass spectrometry has been the predominant means of investigating ion-molecule reactions. The direct identification of reactant and product ions is appealing, at least in part, because of the conceptual simplicity of this approach. However, the neutral products of ion-molecule reactions cannot be determined directly and must be inferred. Gross chemical measurements can serve as an auxiliary technique since they allow identification of un-... 

Johnson SG, Fearey BL (1993) Spectroscopic study of thorium using continuous-wave resonance ionization mass-spectrometry with rrltraviolet ionization. Spectrochim Acta Part B 48 1065-1077 Knoll GF (1989) Radiation Detection and Measurement. J. Wiley and Sons, New York Kuss HM (1992) Applications of microwave digestion technique for elemental analyses. Fresenins J Anal Chem 343 788-793... 

---