Laser 466 Mass Spectrometry Basics

Secondary Ion Mass Spectrometry Basic Concepts, Instrumental Aspects, Applications and Trends. By A. Benninghoven, F. G. Ruenauer, and H.W.Werner Analytical Applications of Lasers. Edited by Edward H. Piepmeier Applied Geochemical Analysis. By C. O. Ingamells and F. F. Pitard Detectors for Liquid Chromatography. Edited by Edward S.Yeung Inductively Coupled Plasma Emission Spectroscopy Part 1 Methodology, Instrumentation, and Performance Part II Applications and Fundamentals. Edited by J. M. Boumans... 

The general principle of detection of free radicals is based on the spectroscopy (absorption and emission) and mass spectrometry (ionization) or combination of both. An early review has summarized various techniques to detect small free radicals, particularly diatomic and triatomic species.68 Essentially, the spectroscopy of free radicals provides basic knowledge for the detection of radicals, and the spectroscopy of numerous free radicals has been well characterized (see recent reviews2-4). Two experimental techniques are most popular for spectroscopy studies and thus for detection of radicals laser-induced fluorescence (LIF) and resonance-enhanced multiphoton ionization (REMPI). In the photochemistry studies of free radicals, the intense, tunable and narrow-bandwidth lasers are essential for both the detection (via spectroscopy and photoionization) and the photodissociation of free radicals. 

There are at least three possibile ways in which the inhibitor can bind to the active site (1) formation of a sulfide bond to a cysteine residue, with elimination of hydrogen bromide [Eq. (10)], (2) formation of a thiol ester bond with a cysteine residue at the active site [Eq. (11)], and (3) formation of a salt between the carboxyl group of the inhibitor and some basic side chain of the enzyme [Eq. (12)]. To distinguish between these three possibilities, the mass numbers of the enzyme and enzyme-inhibitor complex were measured with matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI). The mass number of the native AMDase was observed as 24766, which is in good agreement with the calculated value, 24734. An aqueous solution of a-bromo-phenylacetic acid was added to the enzyme solution, and the mass spectrum of the complex was measured after 10 minutes. The peak is observed at mass number 24967. If the inhibitor and the enzyme bind to form a sulfide with elimination of HBr, the mass number should be 24868, which is smaller by about one... 

Spengler B (2001) The basics of matrix-assisted laser desorption ionization time-of flight mass spectrometry and post source decay. In James P (ed) (2001) Proteome research Mass spectrometry. Springer, New York, p 33... 

Developments in mass spectrometry technology, together with the availability of extensive DNA and protein sequence databases and software tools for data mining, has made possible rapid and sensitive mass spectrometry-based procedures for protein identification. Two basic types of mass spectrometers are commonly used for this purpose Matrix-assisted laser desorption/ionization (MALDI)-time-of-flight (TOF) mass spectrometry (MS) and electrospray ionization (ESI)-MS. MALDI-TOF instruments are now quite common in biochemistry laboratories and are very simple to use, requiring no special training. ESI instruments, usually coupled to capillary/nanoLC systems, are more complex and require expert operators. We will therefore focus on the use of MALDI-... 

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... 

A CEC instrument basically consists of a system for injection (pressure driven or electrokinetic), a column in which the separation takes place, a detector and a high voltage supply (Fig. 16.1). The most commonly used detector so far has been UV with transmission through the capillary outside of the packed bed. Laser induced fluorescence detection has been employed in several studies. Also, mass-spectrometry has been used. Normally, isocratic CEC is performed, but approaches to gradient CEC have been reported [29]. However, special equipment must be employed in most cases. 

Recently, a lot of new exj)eriniental results in supersonic beams have been produced in this field [8]. The basic setup of a cluster experiment is following. First, the clusters are prepared in a supersonic beam. Second, the clusters are photodis-soeiated bt a polarized laser beam, and, third the photodissociated fragments are ionized and detee.ted by techniques of mass spectrometry. 

Various molecular and quasi-molecular ions can be formed under MALDI conditions. The formation of protonated analyte (A) molecules, [A -F H]+, is generally most important at least for samples containing slightly basic centres, such as the peptides and proteins, MALDI mass spectrometry of which is known to be most facile and reproducible. Therefore, proton transfer from the electronically excited, neutral or ionized, or protonated matrix species is considered to be crucial in the overall MALDI process . Notably, proton transfer can occur already in the condensed phase, followed by desorption of the preformed ions . However, the generation of the [A -F H]+ ions is believed to take place preferably in the so-called plume , that is, in the energized, short-hved and relatively dense vapour phase generated above the solid matrix upon excitation by the laser pulse. The actual proton donor species (be it one or several) in a given case is still a matter of... 

F. and Natusch D. F. S. (1982) Laser microprobe mass spectrometry I basic principles and performance characteristics, Anal Chem 54 26A-41A. 

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.

One would expect that basic free amino groups in enzymes could react with acidic supercritical carbon dioxide to form carbamates. Free amino groups exist in lysine, histidine, and arginine. Kamat et al. [20] obtained direct evidence that carbon dioxide forms carbamates with subtilisin, which is a protease with nine lysine groups. They used laser desorption mass spectrometry (LD-MS) to accurately measure the molecular weight increase when subtilisin was placed in dry ice . Subtilisin s molecular weight increased by 176 atomic mass units the weight of four CO2 molecules. The formation of carbamates was reversible. As the dry ice sublimed under vacuum. 

Fitzgerald MC, Parr GR, Smith LM. Basic matrices for the matrix-assisted laser-desorption ionization mass-spectrometry of proteins and oligonucleotides. Anal Chem 1993 65 3204-3211. 

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