Scanning Laser Microprobe Mass Spectrometry

Spengler and Hubert (2002) describe a confocal laser scanning microscope used in conjunction with a TOF mass spectrometer, and also possessing ion imaging 

The output of a Nd YLF laser is focussed by a series of lenses to a spot size of 0.5 pm upon a sample which may be positioned by an x-y-z stepping motor stage and scanned by a computer-controlled high frequency x-y-z piezo stage. Ions are accelerated and transmitted through the central bore of the objective into a time-of-flight (TOF) mass spectrometer. The laser scans an area of 100 x 100 pm with a minimum step size of 0.25 pm. TOF mass spectra of each pixel are evaluated with respect to several ion signals and transformed into two-dimensional ion distribution plots. 

In non-highly focussed laser desorption ionisation, employing spot sizes in the range of 50-200 pm in diameter, the surface is deformed by an ablation volume of about 1 pm3 per pixel per laser pulse. But this ablated volume is spread over a large desorption area leading to ablation depths of the order of a few nanometres. In laser microprobing, the same ablation volume leads to ablation crater depths in the micrometer range. 

Kerridge, D.H. (2000) Proc. Molten State Chemistry, 1, 85. 

Ferraro, J.R. and Basilo, L.J. (1978, 1979) Fourier Transform Infrared Spectroscopy Application to Chemical Systems, New York Academic Press, Vols 1 and 2. 

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Characterization thus involves analytical electron microscopy, ordinary microprobe analysis or other techniques for localizing elements or chemical compounds (Scanning Auger Spectroscopy, Raman Microprobe, Laser Microprobe Mass Spectrometry). It also requires, in most cases, some physical separation of the catalyst for separate analysis (e.g., near surface parts and center of pellets, by peeling or progressive abrasion pellets present at various heights in the catalyst bed, etc.). 

Optical microscopy (OM), polarized light microscopy (PLM), phase contrast microscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), and scanning transmission electron microscopy (STEM) are the methods normally used for identification and quantification of the trace amounts of asbestos fibers that are encountered in the environment and lung tissue. Energy-dispersive X-ray spectrometry (EDXS) is used in both SEM and TEM for chemical analysis of individual particles, while selected-area electron diffraction (SAED) pattern analysis in TEM can provide details of the cell unit of individual particles of mass down to 10 g. It helps to differentiate between antigorite and chrysotile. Secondary ion mass spectrometry, laser microprobe mass spectrometry (EMMS), electron probe X-ray microanalysis (EPXMA), and X-ray photoelectron spectroscopy (XPS) are also analytical techniques used for asbestos chemical characterization. 

Eeckhaoudt S, Van Vaeck L, Gjjbels R and Van Grieken R (1994) Laser microprobe mass spectrometry in biology and biomedicine. Scanning Electron Microscopy supplement 8 335- 358. 

XRD, X-ray diffraction XRF, X-ray fluorescence AAS, atomic absorption spectrometry ICP-AES, inductively coupled plasma-atomic emission spectrometry ICP-MS, Inductively coupled plasma/mass spectroscopy IC, ion chromatography EPMA, electron probe microanalysis SEM, scanning electron microscope ESEM, environmental scanning electron microscope HRTEM, high-resolution transmission electron microscopy LAMMA, laser microprobe mass analysis XPS, X-ray photo-electron spectroscopy RLMP, Raman laser microprobe analysis SHRIMP, sensitive high resolution ion microprobe. PIXE, proton-induced X-ray emission FTIR, Fourier transform infrared. 

Figure 3 Third dimension in pyrolysis mass spectrometry approaches (A) linear programmed thermal degradation mass spectrometry [LPTDMS - third dimension = temperature] (B) collisionally activated dissociation of parent ions coupled with scanning of product ions using tandem mass spectrometry [MS/ MS - third dimension = spectrum of product ions] (C) laser microprobe mass analyser [LAMMA - third dimension = spatial resolution].

Bouschen W, Spengler B (2007) Artifacts of MALDI sample preparation investigated by high-resolution scanning microprobe matrix-assisted laser desorption/ionization (SMALDI) imagine mass spectrometry. Int 1 Mass Spectrom 266 129-137. doi 10.1016/j. ijms.2007.07.017... 

Spengler, B. and Hubert, M. (2002) Scanning Microprobe Matrix-Assisted Laser Desorption Ionization (SMALDI) mass spectrometry instrumentation for sub-micrometer resolved LDI and MALDl surface analysis. J. Am. Soc. Mass Spectrom., 13, 735-748. 

Bouschen, W., Schulz, O., Eikel, D., and Spengler, B. (2010) Matrix vapor deposition/recrystallization and dedicated spray preparation for high-resolution scanning microprobe matrix-assisted laser desorption/ionization imaging mass spectrometry (SMALDl-MS) of tissue and single cells. Rapid Commun. Mass Spectrom., 24, 355-354. 

Impurity inclusions and surface defects are a cause of many difficulties to the polymer producer and user. Equipment used for studying these phenomena discussed in Chapter 4 include electron microprobe x-ray emission/spectroscopy, NMR micro-imaging, various forms of surface infrared spectroscopy, e.g., diffusion reflection FTIR, ATR, also photoacoustic spectroscopy and x-ray diffraction - infrared microscopy of individual polymer fibres. Newer techniques such as scanning electron microscopy (SECM), transmission electron microscopy, time of flight secondary ion mass spectrometry (TOFSIMS), laser induced photoelectron ionisation with laser desorption, atomic force microscopy and microthermal analysis are discussed. 

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