The Mass Spectrometer Overview

In its simplest form, the mass spectrometer has five components (Fig. 3.1), and each will be discussed separately in this chapter. The first component of the mass spectrometer is the sample inlet (Section 3.2), which brings the sample from the laboratory environment (1 atm) to the lower 

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FIGURE 3.1 The components of a mass spectrometer. (Adapted from Gross, J. H., Mass Spectrometry  

In its simplest form, the mass spectrometer has five components (Fig. 8.1), and each will be discussed separately in this chapter. The first component of the mass spectrometer is the sample inlet (Section 8.2), which brings the sample from the laboratory enviromnent (1 atm) to the lower pressure of the mass spectrometer. Pressures inside the mass spectrometer range from a few millimeters of mercury in a chemical ionization source to a few micrometers of mercury in the mass analyzer and detector regions of the instrument. The sample inlet leads to the ion source (Section 8.3), where the sample molecules are transformed into gas phase ions. The ions are then accelerated by an electromagnetic field. Next, the mass analyzer (Section 8.4) separates the sample ions based on their mass-to-charge (miz) ratio. The ions then are counted by the detector (Section 8.5), and the signal 418 

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To summarise, a fractionation step allows the isolation of the compounds of interest from the other molecular constituents, particularly from the fatty acids that are well-ionised. To compensate for the low ionisation yield of some compounds, such as TAGs, the solutions may be doped with a cation. Samples are then directly infused into the ion electrospray source of the mass spectrometer. A first spectrum provides an overview of the main molecular compounds present in the solution based on the peaks related to molecular cations. The MS/MS experiment is then performed to elucidate the structure of each high molecular compound. Table 4.2 shows the different methods of sample preparation and analysis of nonvolatile compounds as esters and TAGs from reference beeswax, animal fats and archaeological samples. 

This chapter does not intend to be a comprehensive coverage of all the inorganic chemistry occurring in mass spectrometers nor does it intend to have much experimental detail of the operation of either the mass spectrometers or the ionization sources. That said, there is a need for a cursory overview of some of the mass spec-trometric techniques (including limitations) used in gas-phase chemistry. 

Fig. 2 Schematic overview of a GC/C/IRMS for determination of values. Following headspace injection or enrichment with SPME or purge Trap the analytes were separated hy GC. After separation the target analytes were completely combusted to CO2 and H2O hy using a PT/NiO/CuO catalyst containing combustion oven. Water is removed by a Nafion membrane to prevent formation of C02H (m/z 45) during ionization. Following combustion the CO2 is ionized in the ion source of the mass spectrometer. After ionization the formed isotopologues C02 (m/z 44), C02 (m/z 45) and (m/z...

The aim of this chapter is to provide an overview of the instrumentation currently available for the mass analysis of MALDI ions. It is not intended as an exhaustive treahse on each instrument, and consequently if more detail is required the reader should examine the Usted reference material in detail. In the first sections of the chapter, the use of lasers for MALDI is discussed, and how they are coupled to the mass spectrometer, together with details of vibrational cooling and tandem mass spectrometry of MALDI ions. This is followed by a description of the different mass analyzer designs, with emphasis placed on commercially available instrument configurations. Definitions of aU acronyms, as well as technical descriptions of terms (such as peak centroid and resolving power) are included at the end of the chapter. 

Central to any measurements in mass spectrometry is the ionization of the sample molecules, and transfer of those ions into the vacuum required for operation of the mass spectrometer. The choice of ionization methods available to analytical and organic mass spectrometrists has expanded greatly in the past ten years, and now includes means for the ionization of nonvolatile as well as volatile molecules. Any of several methods might be chosen to address a particular problem, and each might provide satisfactory results. Since there is no single ionization method used exclusively with TLC/MS, this section of the chapter contains an overview of the most common methods of sample molecule ionization in mass spectrometry. 

Usually a quadrupole mass spectrometer is used, but double focusing instruments are also possible. Two modes of operation are employed. Either the mass spectrometer may be set to select a single m/z ratio and monitor a single ion, or the mass spectrum may be scaimed to provide a complete overview of all m/z ratios and ions. 

The advent of ultrafast pump-probe laser techniques62 and their marriage with the TOF method also enables study of internal ion-molecule reactions in clus-ters.21,63-69 The apparatus used in our experiments is a reflectron TOF mass spectrometer coupled with a femtosecond laser system. An overview of the laser system is shown in Figure 4. Femtosecond laser pulses are generated by a colliding pulse mode-locked (CPM) ring dye laser. The cavity consists of a gain jet, a... 

The instruments may be operated in different detection modes depending on the objectives of the work. Table 2.4.1 gives an overview of the distinct modes of quadrupole mass spectrometers in terms of application, content of information and sensitivity. 

This textbook provides an overview of biomedical mass spectrometry with particular emphasis on GC/MS and quantitative methods. In addition, descriptions are provided of the various types of mass spectrometers and ionization techniques that are used for biomedical applications. 

It has been the purpose of this paper to provide an overview of the basic differences and similarities of the various types of Instruments which detect Ionized particles emitted from surfaces by energetic particle bombardment. Since the scope of secondary ion mass spectrometry Is so broad, It is not surprising that no one Instrument has been designed to perform optimally for all types of SIMS analyses. Design aspects of the primary beam, extraction optics, mass spectrometer, detection equipment and vacuum system must be considered to construct an Instrument best suited for a particular purpose. 

High-quality MSI experiments can be performed with almost all modem mass spectrometers provided the tissues have been prepared accordingly and the experiment is well suited to the capabilities of the instrument. The overview provided in Table 4 has been included as a guide to which applications are suited to the different mass analyzers. New developments in mass spectrometers will undoubtedly offer further improvements in sensitivity, speed, mass resolution, spatial resolution, and identification capabilities. Currently, the main factors limiting the broad application of MSI are sample preparation and the efficient analysis of the large, high-dimensionality datasets. 

An impressive diversity of mass analyzers are utilized in modem analytical instrumentation. An overview of the common mass spectrometer analyzers follows, with particular emphasis on linear quadrupole mass analyzers, quadrupole ion traps, and time-of-flight mass analyzers, as they arguably constitute the quantitative MS workhorses of the pharmaceutical industry. The description of alternate analyzer systems should provide a framework in which the utility of these three particular systems provides the most cost-effective analytical mass spectrometer systems for pharmaceutical analysis. 

More exact production methods have been developed during the last decade for clusters in beams but with the drawback that these methods only produce microscopic aunounts of clusters. These developments go back to the classical work on molecular and atomic beams by Ramsey [35] and recent overviews have been given by Scoles [80], de Heer [54] and Haberland [55]. The first modern production of metal and carbon clusters was accomplished by Furstenau and Hillenkamp [81] using the laser microprobe mass spectrometer, LAMMA,... 

The stable carbon isotope ratios of dissolved inorganic carbon (DIC) and benthic foraminiferal calcite generally are determined with isotope ratio gas mass spectrometers calibrated via NBS 19 international standard to the VPDB (Vienna Pee Dee Belemnite) scale. All values are given in 8-notation versus VPDB with an overall precision of measurements including sample preparation usually better than +0.06 and +0.1%o for calcite and DIC carbon isotopes, respectively. Except one single-specimen based dataset (Hill et al. 2004), all stable isotope data from papers referred to in this overview are from species-specific multi-specimens analyses. The number of specimens used for a single analysis depended on size and weight of species but usually varied between 2 and 25. 

One of the methods of studying the composition of macromolecular sedimentary organic matter in more detail is the molecular analysis of pyrolysis products. For this purpose, the pyrolysis products are transferred to a gas chromatographic column and analyzed as described for extractable organic matter in Sect. 4.5.5, with or without the combination with a mass spectrometer. Both flash pyrolysis (Curie-point pyrolysis samples are heated on a magnetic wire by electrical induction almost instantaneously, e.g., to 610°C) or off-line pyrolysis at various heating rates have been applied to geological samples (see Larter and Horsfield 1993 for an overview of various pyrolysis techniques). 

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