Desorption mass spectrometry

In commercial two-step laser based DI instruments [172] ultra-fast heating of solid samples by pulsed CO2 laser irradiation, which allows desorption of labile compounds without thermal decomposition, is followed by supersonic jet cooling and REMPI. The second laser wavelength excites the analyte to an intermediate energy level and absorption of an additional photon causes ionisation. 

In this Chapter the prospects of laser-based desorption/ionisation (LDI) mass spectrometric techniques for polymer/additive analysis are critically evaluated. 

Principles and Characteristics Analytes with low volatility may be analysed by a variety of desorption techniques e.g. FAB, FD, PD, SIMS, LD). These involve solid samples being bombarded with atoms, ions or photons. Mass spectrometric techniques such as FAB, PD and LD contribute significantly to the characterisation of complex substances [173-175]. In most cases the tech- 

Lasers can be used to achieve a one-step desorption-ionisation process (DLI, direct laser ionisation). The two physical processes involved are laser desorption and ionisation of the desorbed species. The first process depends mainly on the absorbed energy and volatility of the sample, while the second process depends principally on the ionisation potential of the desorbed species. In this case, the desorption laser also acts as the ionisation laser, limiting the ion yield and ultimately, the sensitivity. 

Laser desorption (ionisation) - mass spectrometry (LDMS or one-step LDI-MS) experiments may be manipulated by varying (i) sample presentation (ii) power density, wavelength and pulse duration of the laser desorption technique to ablate the sample and (Hi) mass analyser type combined with a suitable ionisation mode. At variance to MALDI experiments in LDI-MS no matrix is required and no special sample preparation of any kind is necessary. The sample can be subjected to the pulsed desorption laser in a variety of ways. Most commonly, the sample is presented as a solid layer, deposited from solution, on a substrate, which absorbs at the laser wavelength. There is a well-defined threshold, above which successful desorption of neutrals can 

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Laser-desorption mass spectrometry (LDMS) or matrix-assisted laser desorption ionization (MALDI) coupled to a time-of-flight analyzer produces protonated or deprotonated molecular ion clusters for peptides and proteins up to masses of several thousand. 

Beckey, H.D., Principles of Field Ionisation and Field Desorption Mass Spectrometry, Pergamon Press, Oxford, 1977. 

Prokai, L., Field Desorption Mass Spectrometry, Marcel Dekker, New York, 1990. 

Mass Spectrometry. Field desorption mass spectrometry has been used to analy2e PPO (179). Average molecular weight parameters (M and could be determined using either protonated (MH + ) or cation attachment (MNa + ) ions. Good agreement was found between fdms and data supphed by the manufacturer, usually less than 5% difference in all cases up to about 3000 amu. Laser desorption Fourier transform mass spectrometry was used to measure PPG ion and it was claimed that ions up to m/2 9700 (PEG) can be analy2ed by this method (180). 

Other methods of sensitive detection of radiotracers have been developed more recently. Eourier transform nmr can be used to detect (nuclear spin 1/2), which has an efficiency of detection - 20% greater than that of H. This technique is useful for ascertaining the position and distribution of tritium in the labeled compound (14). Eield-desorption mass spectrometry (fdms) and other mass spectral techniques can be appHed to detection of nanogram quantities of radiolabeled tracers, and are weU suited for determining the specific activity of these compounds (15). 

Matrix-assisted laser desorption mass spectrometry (MALDI-MS) is, after electrospray ionization (ESI), the second most commonly used method for ionization of biomolecules in mass spectrometry. Samples are mixed with a UV-absorbing matrix substance and are air-dried on a metal target. Ionization and desorption of intact molecular ions are performed using a UV laser pulse. 

Field desorption mass spectrometry radiopharmacological agents, 6,976 Filter dyes photography, 6, 104 Fissile material criticality... 

Bob Ardrey obtained a first degree in Chemistry from the University of Surrey where he went on to obtain his doctorate stndying the chemistry of trans-2,3-dichloro-l,4-dioxan and the stereochemistry of its reaction prodncts using primarily mass spectrometry and nnclear magnetic resonance spectroscopy. He then carried ont post-doctoral research at King s College, London, into the development of emitters for field-desorption mass spectrometry. 

Tuszynski, W. et al.. The observation of chlorophyll a aggregates with plasma desorption mass spectrometry, in Proceedings of the 5th International Conference of Ion Formation from Organic Solids (IFOS V), Hedin, A., Sundqvist, B.U.R. and Ben-ninghoven. A., Eds., Wiley, Chichester, England, 1989. 

Evans, N. et al.. Applications of high-pressure liquid chromatogrphy and field desorption mass spectrometry in studies of natural porphyrins and chlorophyll derivatives, J. Ghromatogr, 115, 325, 1975. 

Field desorption mass spectrometry [1606], C nuclear magnetic resonance, and fourier-transform infrared spectroscopy [1337] have been used to characterize oil field chemicals, among them, scale inhibitors. Ion... 

P.A. Lyon (ed.), Desorption Mass Spectrometry, American Chemical Society, Washington, DC (1985). 

Automated organic and elemental ion mapping of TLC plates by LMMS techniques, without focus correction, has been reported [802,839]. One of the early TLC-MS scanners used laser desorption combined with Cl detection [807,808]. The use of laser desorption mass spectrometry (LDMS), in connection with TLC separations, allows sampling of a very small area of a spot (ca. 5 im). In this way spot homogeneity can be determined (e.g. in the case of overlapping components), and also leaves the bulk of the material unaffected for further study. An important advantage... 

FD-MS, FDMS Field desorption mass spectrometry GCO Gas chromatography-olfactometry... 

LDMS Laser desorption mass spectrometry desorption/ionisation... 

Beckey, H. D. Principles of Field Ionization and Field Desorption Mass Spectrometry. Oxford Pergamon Press 1977... 

Posthumus, M. A. Kistemaker, P. G. Meuzelaar, H. L. C. Laser desorption-mass spectrometry of polar nonvolatile bio-organic molecules. Anal. Chem. 1978, 50, 985-991. 

MALARIA DETECTION BY LASER DESORPTION MASS SPECTROMETRY... 

Demirev, P. A. Feldman, A. B. Kongkasuriyachai, D. Scholl, P. Sullivan, D. J. Kumar, N. Detection of malaria parasites by laser desorption mass spectrometry. 

Fenyo, D. Chait, B. T. Johnson, T. Lindsey, J. S. Laser desorption mass spectrometry of synthetic multiporphyrin arrays. J. Porph. Phthalocyan. 1997, 1, 93-99. 

Spengler, B. Kirsch, D. Kaufmann, R. Metastable decay of peptides and proteins in matrix-assisted laser-desorption mass spectrometry. Rapid Comm. Mass Spectrom. 1991, 5,198-202. 

Mass spectral data have also been employed for biological studies aimed at determining the distribution of quinolizidine alkaloids within a plant. For instance, the analysis of stem sections of Lupinus polyphyllus and Cytisus scoparius by laser desorption mass spectrometry led to the conclusion that these alkaloids are restricted to the epidermis and probably also to the neighboring one or two subepidermal cell layers <1984MI230>. 

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