Key principles in mass spectrometry

TOF mass analysis is based on the simple principle that molecular and fragment ions are separated as a function of ion velocities. Ions are all accelerated with the same electrostatic potential and hence acquire the same total kinetic energy. Accordingly, after acceleration to a constant kinetic energy (equivalent to zV, where is the accelerating electrostatic potential), ions travel at a velocity, v, that is related to m/z according to 

One of the rods has been cut-away in the diagram to illustrate the complex trajectories of analyte ions trapped between the electrodes. For a given potential cycling between opposing rods, a molecular ion with a certain weight m/z will be enabled to follow a zero-field trajectory to the detector. Changes in potential, change the m/z values of detectable analyte ions. 

4 Fourier transform ion cyclotron resonance (FTICR) mass analysers 

Tandem mass analysis, also known as mass spectrometry/mass spectrometry (MS/MS), results from the coupling together of two consecutive mass analysers in a mass spectrometer so as to obtain further information regarding the sample. Typically, there are three stages to tandem mass analysis  

Matrix-assisted laser desorption/ionization Extraction grid (MALDI) 

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While mass spectrometry cannot provide the detailed structural information that is obtained by NMR and X-ray crystallography, it can, in principle, provide valuable information on the formation and stoichiometry of nonco-valent complexes. There are several key questions that need to be addressed before we can decide whether the advantages of mass spectrometry (sensitivity, speed, and specificity) can be successfully applied to the study of nonco-valent interactions. These questions are... 

For detection of carbohydrates in principle, ultraviolet (UV), laser-induced fluorescence, refractive index, electrochemical, amperometric, and mass spec-trometric detection can be used. Mass spectrometry, with its various ionization methods, has traditionally been one of the key techniques for the structural determination of proteins and carbohydrates. Fast-atom bombardment (FAB) and electrospray ionization (ESI) are the two on-line ionization methods used for carbohydrate analysis. The ESI principle has truly revolutionized the modern mass spectrometry of biological molecules, due to its high sensitivity and ability to record large-molecule entities within a relatively smaU-mass scale. 

Time-of-flight mass spectrometry (TOFMS) is probably the simplest method of mass spectrometric measurement by the physical principle. The key features of TOFMS are extreme sensitivity (all ions are detected), practically unlimited mass range and as well as high-speed analysis (recent TOFMS instruments are able to measure hundreds full spectra per second). This all makes TOFMS one of the most desirable methods of mass analysis (Schlag, 1994 Guilhaus, 1995). The general scheme of TOFMS is shown in Scheme 1. 

In VoL 2 of this handbook, the origin of elements has been discussed in detail. Therefore, the present authors will exclude that part, except for some comments on the importance of particular radionucKdes. In this chapter, the principles and instrumentation of accelerator mass spectrometry (AMS), the key player for detection of cosmological radionucKdes in ultra trace scale, will be discussed in detail. Detailed discussion of all the research works carried out to date with cosmogenic radionuclides is out of scope. Only the detection of million-year half-life radionucKdes in ultra trace concentration will be touched, followed by concise description of the required chemistry. Rather than giving a general description, a few of them have been chosen and described in separate sections. Inductively coupled plasma-mass spectrometry (ICP-MS), thermal ionization mass spectrometry (TIMS), secondary ion mass spectrometry (SIMS), or resonant laser ionization mass spectrometer (RIMS), etc. have also been used for detection of cosmogenic radionucKdes. However, these techniques have much lower sensitivity compared to AMS. Brief discussions on these instruments have been appended at the end of this chapter. This chapter ends with a conclusion. 

MicroChannel Plates. One type of array transducer for mass spectrometry is the electrooptical ion detector (EOID) shown in Figure ll-4a. The key clement in the EOID is the microchannel electron multiplier, or microchannel plate, which is referred to in some optical applications as an image intensilier. The design and basic principles of operation of the microchannel plate are illustrated in Figure 1 l-4b. The plate consists of an array of tiny lubes (diameters as small as 6 pm)... 

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