Basic Principles of Mass Spectrometry

The wide popularity of mass spectrometry is the result of its unique capabilities  

The first step is ionization that converts analyte molecules or atoms into gas-phase ionic species. This step requires the removal or addition of an 

The next step is the separation and mass analysis of the molecular ions and their charged fragments on the basis of their mjz (mass-to-charge) ratios. 

Finally, the ion current due to these mass-separated ions is measured, amplified, and displayed in the form of a mass spectrum. 

The first two steps are carried out under high vacuum, which allows ions to move freely in space without colliding or interacting with other species. Collisions may lead to fragmentation of the molecular ions and may also produce a different species through ion-molecule reactions. These processes will reduce sensitivity, increase ambiguity in the measurement, and decrease resolution. In addition, the atmospheric background will introduce interference. 

INSTRUMENTATION AND TECHNIQUES BASIC PRINCIPLES OF MASS SPECTROMETRY A mass spectrum is produced by ionizing the molecules of a compound 

There are several textbooks which discuss the physical principles involved in mass spectrometry and the fundamental aspects of mass spectrometer design and operation [15-17]. However, it is worthwhile considering briefly the way in which the mass spectra of organic compounds are produced and recorded, together with the instrumentation and techniques most commonly employed in GC-MS. 

In the process the bombarding electron transfers excess energy to the ion which, if sufficient, results in the instability of atomic bonds leading to the formation of fragment ions. Although a variety of atomic and 

Changing either H or V alters the deflection path of the ions. In normal 

The mass resolution of magnetic instruments is expressed as M/AM where AM is the mass difference between mass M and the next higher mass from which it is being separated. An overlap of the two peaks leading to a 10% valley has been selected arbitrarily for a working definition of unit resolution. 

---

II. The Basic Principles of Mass Spectrometry of Organic Compounds. 40... 

This book is divided into three parts. The first section contains introductory chapters on MS and MSI. Chapter I provides an overview of MSI and focuses on current and future trends in the field. The success of a particular MSI experiment depends on the specific MS approach used. Therefore, the second chapter describes the basic principles of mass spectrometry relevant to MSI and includes cross-references to other chapters of this volume for easier navigation. The third chapter reviews the application of MSI to the study of elemental distributions. Following these introductory chapters, there are multiple protocols that describe qualitative and quantitative measurements of endogenous metabolites and xenobiotics as well as their identification and localization. The last section includes protocols for a variety of MSI approaches developed to study peptide and protein distributions. The experimental protocols presented herein encompass most MSI approaches and technologies for samples from a wide range of biological models including plants, invertebrates, and vertebrates. 

Although the basic principle of mass spectrometry (MS) was discovered as early as 1910 by Sir J. J. Thomson, it was not untU the end of World War II that MS was first developed for analyses of gas and hydrocarbon mixtures [1], Almost all of the mass spectrometers at that time were made by researchers or specialists. The first commercial mass spectrometer manufactured by Consolidated Engineering Corporation (CEC) was delivered to the Atlantic Refining Company in 1946 for analysis of hydrocarbon fractions in gasoline boiling range [2]. Since then, the petroleum industry has pioneered the use of MS in chemical research. Many advances in MS were driven by the needs of the petroleum industry for analyzing components in complex mixtures. 

In contrast to IR and NMR spectroscopy, the principle of mass spectrometry (MS) is based on decomposition and reactions of organic molecules on theii way from the ion source to the detector. Consequently, structure-MS correlation is basically a matter of relating reactions to the signals in a mass spectrum. The chemical structure information contained in mass spectra is difficult to extract because of the complicated relationships between MS data and chemical structures. The aim of spectra evaluation can be either the identification of a compound or the interpretation of spectral data in order to elucidate the chemical structure [78-80],... 

The basic principle underlying mass spectrometry was formulated by J. J. Thomson (the discoverer of the electron) early in the century. Working with cathode ray tubes, he was able to separate two types of particles, each with a slightly different mass, from a beam of neon ions, thereby proving the existence of isotopes. (Isotopes are atoms of the same element that have slightly different atomic masses due to the presence of differing numbers of neutrons in the nucleus.) The first mass spectrometers were built in 1919 by F. W. Aston and A. J. Dempster. 

Except for a brief introduction to the principles and basic definitions of mass spectrometry, aspects of instrumentation, sample handling and specific techniques will not be discussed. These and other pertinent de-... 

Figure 1.1. Basic concept of mass spectrometry analysis. (Reproduced from C. Dass, Principles and Practice of Biological Mass Spectrometry, Wiley-Interscience, 2001.)...

The basic principles of fast-atom bombardment (FAB) and liquid-phase secondary ion mass spectrometry (LSIMS) are discussed only briefly here because a fuller description appears in Chapter 4. This chapter focuses on the use of FAB/LSIMS as part of an interface between a liquid chromatograph (LC) and a mass spectrometer (MS), although some theory is presented. 

The result of the Back-to-Basics series is an accumulation of some 50 separate but interrelated expositions of mass spectrometric principles and apparatus. Some areas of mass spectrometry, such as ion cyclotron resonance and ion trap instruments, have not been covered except for passing references. This decision has not been due to any bias by the authors or Micromass but simply reflects the large amount of writing that had to be done and the needs of the greatest proportion of users. 

The abundance of a trace element is often too small to be accurately quantihed using conventional analytical methods such as ion chromatography or mass spectrometry. It is possible, however, to precisely determine very low concentrations of a constituent by measuring its radioactive decay properties. In order to understand how U-Th series radionuclides can provide such low-level tracer information, a brief review of the basic principles of radioactive decay and the application of these radionuclides as geochronological tools is useful. " The U-Th decay series together consist of 36 radionuclides that are isotopes (same atomic number, Z, different atomic mass, M) of 10 distinct elements (Figure 1). Some of these are very short-lived (tj j 1 -nd are thus not directly useful as marine tracers. It is the other radioisotopes with half-lives greater than 1 day that are most useful and are the focus of this chapter. 

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. 

Under the headline of instmmentation we shall mainly discuss the different types of mass analyzers in order to understand their basic principles of operation, their specific properties and their performance characteristics. Of course, this is only one aspect of instmmentation hence topics such as ion detection and vacuum generation will be addressed in brief. As a matter of fact, sample introduction is more closely related to particular ionization methods than to the type of mass analyzer employed, and therefore, this issue is treated in the corresponding chapters on ionization methods. The order of appearance of the mass analyzers in this chapter neither reflects the ever-changing percentage they are employed in mass spectrometry nor does it strictly follow a time line of their invention. Instead, it is attempted to follow a trail of easiest understanding. 

From its very beginnings to the present almost any physical principle ranging from time-of-flight to cyclotron motion has been employed to construct mass-analyzing devices (Fig 4.1). Some of them became extremely successful at the time they were invented, for others it took decades until their potential had fully been recognized. The basic types of mass analyzers employed for analytical mass spectrometry are summarized below (Tab. 4.1). 

The basic principles of absorption spectroscopy are summarised below. These are most obviously applicable to UV and IR spectroscopy and are simply extended to cover NMR spectroscopy. Mass Spectrometry is somewhat different and is not a type of absorption spectroscopy. 

The scope of the use of mass spectrometry in the protein analysis has grown enormously in the past few decades. MS has become an important analytical tool in biological and biochemical research. Its speed, accuracy and sensitivity are unmatched by conventional analytical techniques. The variety of ionization methods permits the analysis of peptide or protein molecules from below 500 Da to as big as 300 Da (Biemann 1990 Lahm and Langen 2000). Basically, a mass spectrometer is an instrument that produces ions and separates them in the gas phase according to their mass-to-charge ratio (m/z). The basic principle of operation is to introduce sample to volatilization and ionization source, and then the molecular fragments from the ionization of the sample are detected by various kinds of detector and the data are analyzed with computer software. 

Before describing the application of Nuclear magnetic resonance (NMR) spectroscopy to potentized homeopathic drugs we would first discuss the basic principles of NMR spectroscopy. This spectroscopy is a powerful tool providing structural information about molecules. Like UV-visible and infra red spectrometry, NMR spectrometry is also a form of absorption spectrometry. Nuclei of some isotopes possess a mechanical spin and the total angular momentum depends on the nuclear spin, or spin number 1. The numerical value of I is related to the mass number and the atomic number and may be 0, Vi, 1 etc. The medium of homeopathic... 

The basic principle of FT/ICR mass spectrometry is that a moving ion in an applied static magnetic field undergoes circular motion, in a plane perpendicular to that field, at a "cyclotron" frequency, U3 ... 

Whereas in LIMS only one laser with defined wavelength (e.g., Nd YAG - 1064 nm) is used for direct vaporization and ionization of solid samples in laser plasma, in resonance ionization mass spectrometry (RIMS) " one or more lasers are tuned precisely to the wavelength required for the excited states and ionization of evaporated atoms in order to get a highly selective ionization of the analyte. The basic principles of resonant ionization were first described by Hurst and coworkers at Oak Ridge National Laboratory as well as by Letokhov et in Russia. The technology... 

---