Performance of Mass Spectrometers

Vapor pressures of phases in these systems were measured by the Knudsen effusion technique. Use of mass spectrometer-target collection apparatus to perform thermodynamic studies is discussed. The prominent sublimation reactions for these phases below 2000 K was shown to involve formation of elemental plutonium vapor. Thermodynamic properties determined in this study were correlated with corresponding values obtained from theoretical predictions and from previous measurements on analogous intermetallics. 

Michael Story is retired from Thermo Electron Corporation. He was involved in the research, design, and commercialization of mass spectrometers for 37 years, and is a cofounder of the Finnigan Corporation. He was a member of previous NRC committees on commercial aviation security (1988-1993) and chaired the Panel on Test Protocol and Performance Criteria. 

Consider one small molecule, phenylalanine. It is an essential amino acid in our diet and is important in protein synthesis (a component of protein), as well as a precursor to tyrosine and neurotransmitters. Phenylalanine is one of several amino acids that are measured in a variety of clinical methods, which include immunoassay, fluorometry, high performance liquid chromatography (HPLC see Section 4.1.2) and most recently MS/MS (see Chapter 3). Historically, screening labs utilized immunoassays or fluorimetric analysis. Diagnostic metabolic labs used the amino acid analyzer, which was a form of HPLC. Most recently, the tandem mass spectrometer has been used extensively in screening labs to analyze amino acids or in diagnostic labs as a universal detector for GC and LC techniques. Why did MS/MS replace older technological systems The answer to this question lies in the power of mass spectrometer. 

In principle, the analytical results obtained by the GPC spin column/HPLC ESI-MS methodology described in this chapter should be similar to the results obtained using the tandem chromatographic method of GPC/reversed-phase HPLC ESI-MS described in Chapter 3. There are practical advantages for each method. Since each of the chromatographic and mass spectral steps are done serially for the GPC spin column/HPLC ESI-MS methodology, each of the steps can be performed and optimized individually. In the event of mass spectrometer failure, the production of spin column eluate samples can proceed and samples can be stored for future analysis. In contrast, the parallel methodology of tandem GPC/ reversed-phase HPLC ESI-MS requires the simultaneous optimization of multi-... 

Fig. 8.1.1 Simple illustrations of a various mass spectrometers, a The triple-quadrupole tandem mass spectrometer (top panel). The middle set of quadrupoles are part of the collision cell (CC) and do not perform mass separation. MSI and MS2 indicate the first and second quadrupole mass separation devices, respectively. The bold arrow shows the path of ions, b Ion-trap mass spectrometer (middle left). The charged sections of the ion trap are not elliptical as drawn, but rather hyperbolic. The diagram is also two-dimensional, whereas the ion trap is three-dimensional. The ion path is such that ions enter the device and are trapped until a specific voltage ejects these ions, c Time of Flight mass spectrometer with a Reflectron (middle left). Ions are separated by the time it takes to pass through the instrument. The Reflectron improves/focuses the ions, d Hybrid Tandem mass spectrometer (bottom). The diagram shows that a quadrupole instrument can be combined with a different type of mass spectrometer, forming a tandem hybrid instrument...

A few years ago, we began a research program to develop methods of analysis which would involve the use of FAB and a high performance tandem mass spectrometer. The tandem instrument was the first triple sector mass spectrometer to be designed and built by a commercial instrument company (Kratos of Manchester, U.K.). The first mass spectrometer of the combination is a double focussing Kratos MS-50 which is coupled to a low resolution electrostatic analyzer, which serves as the second mass spectrometer U). This FAB MS-MS combination has been used to verify the structures of an unknown cyclic peptide (2), a new amino acid modified by diphtheria toxin (3), and an ornithine-containing lipid (4). A number of methods have also been worked out which rely on this instrumentation. They Include the structural determination of cyclic peptides (5), nucleosides and nucleotides (6), and unsaturated fatty acids (7) and the analysis of mixtures of both anionic (8) and cationic surfactants (9). 

This chapter first presents a review of the rapidly developing range of MC-ICP-MS instrumentation available, then briefly surveys the initial experiments and associated methodologies that have helped to characterize the current and predicted performance of this kind of mass spectrometer, and concludes with a description of the exciting research areas, previously considered to be intractable, that are now developing in the earth sciences, cosmochemistry, oceanography, and the life sciences as a direct consequence of this technique. 

Besides the triple quadrupol instruments, other types of mass spectrometers might be used as well. Examples for these types of instruments are ion traps, time of flight mass spectrometers and also single quadrupol mass analyzers. Due to the characteristic and specific advantages and disadvantages of different instrument types, the overall assay performance (e.g. sensitivity, dynamic range and selectivity) may vary quite a bit from one instrument type to the other. 

The ability to apply customized waveforms to the QIT, together with the fact that ions are trapped and therefore can be subjected to different treatment over a period of time, makes the QIT one of the most versatile of mass spectrometers, rivaled only by the ICR mass spectrometer. This is most strongly evident in tandem mass spectrometry (MS/MS and related techniques), which will be discussed separately. It should be noted here, however, that multiple stage MS/MS experiments (MS/MS/MS.. ., or MS ) experiments are readily performed in ion traps. 

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