An Introduction to Mass Spectrometry

Mass spectrometry (MS) involves formation of ions in a mass spectrometer followed by separation and detection of the ions according to mass and charge. A mass spectrum is a graph that on the x-axis represents the formula weights of the detected ions, and on the y-axis represents the abundance of each detected ion. The x-axis is labeled m/z, where m = mass and z = charge. In examples we shall consider, z equals +1, and hence the x-axis effectively represents the formula weight of each detected ion. The y-axis expresses relative ion abundance, usually as a percentage of the tallest peak or directly as the number of detected ions. The tallest peak is called the base peak. As a typical example, the mass spectfum of propane is shown in Fig. 9.35. 

A The x-axis, in units of m/z, teptesents the foimula weight of the detected ions, /tvfeis the mass (m) to charge (z) ratio. Because z is typicaiiy +1, m/z represents the formuia weight of each ion. 

B The y-axis represents the reiative abundance of each detected ion. 

C The most abundant ion (taiiest peak) is caiied the base peak. The base peak is usuaiiy an easiiy formed fragment of the original compound, in this case it is an ethyi fragment (CjFig, m/z29). 

D One of the higher vaiue m/z peaks may or may not represent the molecular ion (the ion with the formuia weight of the originai compound). When present, the moiecuiarion (m/z 44 in the case of propane) is usuaiiy not the base peak, because ions from the originai moiecuie tend to fragment, resuiting in the other m/z peaks in the spectmm. 

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Beynon, J.H. and Brenton, A.G. (1982). An Introduction to Mass Spectrometry. University of Wales Press, Cardiff. 

Kicman, A.T., Parkin, M.C., and lies, R.K. (2007) An introduction to mass spectrometry based proteomics-detection and characterization of gonadotropins and related molecules. Molecular and Cellular Endocrinology, 260-262,212-227. 

The introductory chapter is brief but provides an ample introduction to mass spectrometry and leaves one comfortable as he/she moves on to the historical and instrumentation chapters that follow. A few of the basic equations are given as part of the review of basic concepts. In these few pages Dr Becker clearly introduces the concepts of atomic mass units relative to carbon, isotopes and isotope abundance. Figures 1.1 and 1.2 go hand in hand in providing the reader with the three major parts of a mass spectrometer (source, ion separation, detection) and show various alternatives for each of these. The subtle use of color in these and subsequent figures adds an attractive benefit for the reader. 

Figure 4.16. MALDI-TOF Mass Spectrometry. (1) The protein sample, embedded in an appropriate matrix, is ionized by the application of a laser beam. (2) An electrical field accelerates the ions formed through the flight tube toward the detector. (3) The lightest ions arrive first. (4) The ionizing laser pulse also triggers a clock that measures the time of flight (TOF) for the ions. [After J. T. Watson, Introduction to Mass Spectrometry, 3d ed. (Lippincott-Raven, 1997), p. 279.]...

Figure 8.47 Schematic diagram of an electron ionization source. (From Watson, J.T. Introduction to Mass Spectrometry, 3rd ed. Lippincott-Raven Publishers Philadelphia, 1997, p. 140.)...

Analytical figures of merit for ICP-MS, Inductively Coupled Plasma Mass Spectrometry An Introduction to ICP Spectrometries for Elemental Analysis, A. Montasser, Ed., Wiley-VCH, 1998, pp. 16-28, chap. 1.4. 

The use of mass spectrometry for the analysis of peptides, proteins, and enzymes has been summarized. This chapter should be read in conjunction with others, including Chapter 45, An Introduction to Biotechnology, and Chapters 1 through 5, which describe specific ionization techniques in detail. 

The mass spectra of mixtures are often too complex to be interpreted unambiguously, thus favouring the separation of the components of mixtures before examination by mass spectrometry. Nevertheless, direct polymer/additive mixture analysis has been reported [22,23], which is greatly aided by tandem MS. Coupling of mass spectrometry and a flowing liquid stream involves vaporisation and solvent stripping before introduction of the solute into an ion source for gas-phase ionisation (Section 1.33.2). Widespread LC-MS interfaces are thermospray (TSP), continuous-flow fast atom bombardment (CF-FAB), electrospray (ESP), etc. Also, supercritical fluids have been linked to mass spectrometry (SFE-MS, SFC-MS). A mass spectrometer may have more than one inlet (total inlet systems). 

The first part of this book is dedicated to a discussion of mass spectrometry (MS) instrumentation. We start with a list of basic definitions and explanations (Chapter 1). Chapter 2 is devoted to the mass spectrometer and its building blocks. In this chapter we describe in relative detail the most common ion sources, mass analyzers, and detectors. Some of the techniques are not extensively used today, but they are often cited in the MS literature, and are important contributions to the history of MS instrumentation. In Chapter 3 we describe both different fragmentation methods and several typical tandem MS analyzer configurations. Chapter 4 is somewhat of an outsider. Separation methods is certainly too vast a topic to do full justice in less than twenty pages. However, some separation methods are used in such close alliance with MS that the two techniques are always referred to as one combined analytical tool, for example, GC-MS and LC-MS. In effect, it is almost impossible to study the MS literature without coming across at least one separation method. Our main goal with Chapter 4 is, therefore, to facilitate an introduction to the MS literature for the reader by providing a short summary of the basic principles of some of the most common separation methods that have been used in conjunction with mass spectrometry. 

Christianini, N., Shawe-Taylor, J. An Introduction to Support Vector Machines and Other Kernel-Based Learning Methods. Cambridge University Press, Cambridge, NY, 2000. Crawford, L. R., Morrison, J. D. Anal. Chem. 40, 1968, 1469-1474. Computer methods in analytical mass spectrometry. Empirical identification of molecular class. 

Liquid membrane enrichment coupled to mass spectrometry. Membrane introduction mass spectrometry (MIMS) is an established method of sample... 

Chernushevich, I. V. Loboda, A. V. Thomson, B. A. An introduction to quadrupole-time-of-flight mass spectrometry. J. Mass Spectrom. 2001, 36, 849-865. 

This chapter has presented an introduction to Tethering with a focus on how mass spectrometry enables the technology to rapidly find inhibitors to drug... 

This chapter reviews the bioanalytical developments by mass spectrometry in the field of targeted anticancer therapy, across the growing family of recent FDA-approved oral TKIs as well as tamoxifen and its active metabolites. The text also provides an introduction to existing pharmacokinetics-pharmacodynamics knowledge in the field of targeted anticancer therapy. 

Hop, C. E. C. A., and Bakhtiar, R. (1997). An introduction to electrospray ionization and matrix-assisted laser desorption/ionization mass spectrometry—essential tools in a modern biotechnology laboratory. Biospectroscopy 3, 259-280. 

Boyd, R.K., Tandem mass spectrometry quadropole and hybrid instruments, Metftodi nzymo/. 193, 154-200, 1990 Jonscher, K.R. and Yates, J.R., 111, The quadrupole ion trap mass spectrometry — a small solution to a big challenge. Anal. Biochem. 244, 1-15, 1997 Chemushevich, I.V., Loboda, A.V., and Thomson, B.A., An introduction to quadrupole-time-of-flight mass spectrometry, J. Mass Spectrom. 36, 849-865, 2001 Ens, W. and Standing, K.G., Hybrid quadrapole/time-of-flight mass spectrometers for analysis of biomolecules. Methods Enzymol. 402,49-78, 2005 Payne, A.H. and GUsh, G.L., Tandem mass spectrometry in quadrupole ion trap and ion cyclotron resonance mass spectrometers. Methods Enzymol. 402, 109-148, 2005. 

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