Microprobe mass spectrometry

Principles and Characteristics Laser microprobe mass spectrometry (LMMS, LAMMS), sometimes called laser probe microanalysis (LPA or LPMA) and often also referred to as laser microprobe mass analysis (LAMMA , Leybold Heraeus) [317] or laser ionisation mass analysis (LIMA , Cambridge Mass Spectrome-try/Kratos) [318], both being registered trademarks, is part of the wider laser ionisation mass spectrometry (LIMS) family. In the original laser microprobe analyser, emitted light was dispersed in a polychro-mator. Improved sensitivity may be obtained by secondary excitation of ablated species with an electric spark. In the mass spectrometric version of the laser microprobe, ions formed in the microplasma 

For any true microspectrochemical analysis a microscope and a dispersing instrument are needed. An essential feature of a laser microscope is that the objectives for both the observation of the specimen and for focusing the laser radiation must be suitable for ablation, vaporisation, and excitation of the material. The defining attribute of LMMS is the use of a high power pulsed UV laser ultimately focused down to the dil action-limited spot (0.5 ixm at 266 nm) to vaporise, atomise, and ionise a microvolume of a solid specimen in a one-step procedure. Laser microprobe mass analysers are typically equipped with Nd YAG lasers (1064 and 266 nm 5-15 ns pulses) or excimer lasers (XeF, 351 nm XeCl, 308 nm KrF, 248 nm with about 7-30 nm pulses). Power densities of up to 10 Wcm 2 are quite common organic compounds require attenuation to about 10 -10 W cm . By adjusting the laser power, desorption and ionisation can, to some extent, be selected over ablation and dissociation in the microplasma. 

The information contained in these spectra differs as a result of the incomparability of the time domains for sampling and analysis of the laser-generated ions. ToF LMMS registers only the prompt ions whereas FT LMMS detects a different fraction of the initial ion population, namely including the ions from post-laser DI. FT LMMS data thus give access to ions formed during and after the laser pulse [326, 327]. 

After Van Vaeck et a/. [329]. FromL. Van VaeckeraZ., m Surface Characterization. A User s Sourcebook (D. Brune etal., eds.). Copyright 1997 Wiley-VCH, Weinheim. Reproduced with permission. 

ToF LMMS for PET. A clear distinction between ToF and FT LMMS is mandatory, as summarised in Table 3.26. 

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R. W. Odom and B. Schueler. Laser Microprobe Mass Spectrometry Ion and Neutral Analysis, in Lasers and Mass Spectrometry (D. M. Lubman, ed.) Oxford University Press, Oxford, 1990. Presents a useful discussion of LIMS instrumental issues, including the post-ablation ionization technique. Several anal)n ical applications are presented. 

Laser Ionization Mass Spectrometry Laser Microprobe Mass Analysis Laser Microprobe Mass Spectrometry Laser Ionization Mass Analysis Nonresonant Multi-Photon Ionization... 

KF Karl Fischer (coulometry) LMMS Laser microprobe mass spectrometry... 

LASER MICROPROBE MASS SPECTROMETRY 3.3.1 Operating Principle... 

Infrared and ultraviolet probes for surface analysis are then considered.The applications of IR spectroscopy and Raman microscopy are discussed, and a brief account is also given of laser-microprobe mass spectrometry (LAMMA). 

Van Vaeck, L. Struyf, H. Van Roy, W. Adams, F. Organic and inorganic analysis with laser microprobe mass spectrometry. Mass Spectrom Rev. 1994,13,189-208. 

Hara, K., T. Kikuchi, K. Furuya, M. Hayashi, and Y. Fujii, Characterization of Antarctic Aerosol Particles Using Laser Microprobe Mass Spectrometry, Environ. Sci, Technol., 30, 385-391 (1996). 

Linton, R. W., Williams, P., Evans, C. A. Natusch, D. R. S. 1977. Determination of the surface predominance of toxic trace elements in airborne particles by ion microprobe mass spectrometry and Auger electron spectroscopy. Analytical Chemistry, 49, 1514-1521. 

Today the population is becoming increasingly exposed to ultrafine particles (< 20 nm, e.g., Aerosil, 2) in bodycare and household products. Ion microscopy studies revealed that such particles can, for example, penetrate the horny layer of the skin and can result in unexpected interactions. SIMS and Fourier transform laser microprobe mass spectrometry (FT LMMS) have been applied to study 2 stimulated interaction in thin layers of dermatological gels as a result of UV irradiation.175 For future studies of distribution of ultrafine particles LA-ICP-MS will be employed. 

C.-U. Ro and R. W. Linton, New directions in microprobe mass spectrometry molecular microanalysis using neural networks. Microbeam Anal., 1(2), 1992, 75-87. 

Simons, D. S. Laser microprobe mass spectrometry, in Springer Series in Chemical Physics 36 (eds. Benninghoven, A.), et al., p. 158, Berlin, Heidelberg, New York, Tokyo, Springer 1984... 

Very few of these studies were directed at elemental analysis. They concentrated on analysis of molecular ions and on study of the structure and reactivity of cluster ions. Another area of investigation, laser microprobe mass spectrometry using FT-ICR mass analysis [84], has most often been concerned with organic impurities on and in materials. However, it can be used to detect elemental ions produced by the laser desorption process. 

Among the other soft ionization techniques is laser microprobe mass spectrometry (LAMMA) in which a laser pulse is used to vaporize a small amount of sample, as discussed in a 1982 review (108). Of interest to us is the application to the study of some cobalamins (109). (M + H) and (M - H) ions were observed in the positive and negative ion modes, respectively. However, there were few other high-mass fragments that could be used to impart structural information. 

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.). 

Hara K., Kikuchi T., Furuya K., Hayaffii M., and Fujii Y. (1996) Characterization of Antarctic aerosol particles using laser microprobe mass spectrometry. Environ. Sci. Technol. 30, 385-391. 

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

Microprobe techniques, and their detection limits (given in mgkg ), that have been applied to Al localization include energy dispersive (electron probe) X-ray microanalysis (20), wavelength-dispersive X-ray microanalysis, electron energy loss spectrometry (500), proton probe nuclear microscopy (10), resonance ionization mass spectrometry (3), secondary ion mass spectrometry (1), laser microprobe mass spectrometry (1) and micropartide-induced X-ray emission (Yokel 2000). 

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