Mass spectrometry basic components

Figure 1.2 shows the basic instrumentation for atomic mass spectrometry. The component where the ions are produced and sampled from is the ion source. Unlike optical spectroscopy, the ion sampling interface is in intimate contact with the ion source because the ions must be extracted into the vacuum conditions of the mass spectrometer. The ions are separated with respect to mass by the mass analyser, usually a quadrupole, and literally counted by means of an electron multiplier detector. The ion signal for each... 

The development of a robust analytical method is a complex issue. The residue analyst has available a vast array of techniques to assist in this task, but there are a number of basic rules that should be followed to produce a reliable method. The intention of this article is to provide the analyst with ideas from which a method can be constructed by considering each major component of the analytical method (sample preparation, extraction, sample cleanup, and the determinative step), and to suggest modern techniques that can be used to develop an effective and efficient overall approach. The latter portion emphasizes mass spectrometry (MS) since the current trend for pesticide residue methods is leading to MS becoming the method of choice for simultaneous quantitation and confirmation. This article also serves to update previous publications on similar topics by the authors. ... 

Part V covers spectroscopic methods of analysis. Basic material on the nature of light and its interaction with matter is presented in Chapter 24. Spectroscopic instruments and their components are described in Chapter 25. The various applications of molecular absorption spectrometric methods are covered in some detail in Chapter 26, while Chapter 27 is concerned with molecular fluorescence spectroscopy. Chapter 28 discusses various atomic spectrometric methods, including atomic mass spectrometry, plasma emission spectrometry, and atomic absorption spectroscopy. 

The instruments commercially available to perform mass spectrometry are a reflection of the technique itself, very diversified. No matter what their degree of complexity is, they are all composed of similar basic components that can be described as follows a sample introduction inlet, an ion source, a mass analyser, and a detector. 

Mass spectrometry is a sophisticated instrumental technique that produces, separates, and detects ions in the gas phase. The basic components of a mass spectrometer are shown in Figure 20.9. A sample with a moderately high vapor pressure is introduced in an inlet system, operated under vacuum (10"" to 10 ton) and at high temperarnre (up to 300°C). It vaporizes and is carried to the ionization source. Nonvolatile compounds may be vaporized by means of a spark or other... 

Figure 9.2 The basic components of a mass spectrometer. All mass spectrometers consist of an ion source linked to a mass analyser then to a detector. The important ion sources and mass analysers for biological mass spectrometry are listed. There are many other potential ion sources and mass analysers used generally in mass spectrometry, but only the indicated are of use in the analysis of biological macromolecules and amphiphilic lipids, and also in proteomics FAB fast atom bombardment MALDI matrix-assisted laser desorption and ionization ESI electrospray ionization ToF time of flight FTICR fourier transform ion cyclotron resonance MS/MS tandem mass spectrometry.

Figure 1.2. Basic components of a mass spectrometer. (Reproduced from C. Dass, Principles and Practice of Biological Mass Spectrometry, WUey-Interscience, 2001.)...

Intact protein mass spectrometry allows the molecular mass determination of either proteins or complexes of proteins and covalently bound ligands/other proteins. In a first step, the sample is desalted to detach from buffer components and small ions that would interfere through noncovalent complexes in the gas phase. Next, the isolated protein is ionized, for example, by electrospray ionization (ESI). The acid in the eluent causes protonation of the protein at basic sites, particularly lysine and arginine residues, so that m/z values of multiple species with different charges can be measured in a mass spectrometer. These data are then combined during the deconvolution process to yield the mass of the protein or complex. 

The advent of combined gas chromatography/mass spectrometry has made the characterization of the aliphatic portion of the suberin polymer relatively straightforward. It is important that the initial physical isolation of the suberized tissue be done with care as this step determines the degree of suberin-enrichment in the final fraction (235, 243). Treatment of the tissue with hydrolytic enzymes, such as pectinase and cellulase, may remove a considerable portion of the cell wall carbohydrate. Strongly acidic, basic, or oxidizing conditions should be avoided to prevent chemical changes in the suberin components. The final residue is dried. 

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