LASER IONISATION MASS SPECTROMETRY

The technique is referred to by several acronyms including LAMMA (Laser Microprobe Mass Analysis), LIMA (Laser Ionisation Mass Analysis), and LIMS (Laser Ionisation Mass Spectrometry). It provides a sensitive elemental and/or molecular detection capability which can be used for materials such as semiconductor devices, integrated optical components, alloys, ceramic composites as well as biological materials. The unique microanalytical capabilities that the technique provides in comparison with SIMS, AES and EPMA are that it provides a rapid, sensitive, elemental survey microanalysis, that it is able to analyse electrically insulating materials and that it has the potential for providing molecular or chemical bonding information from the analytical volume. 

Microprobe laser desorption laser ionisation mass spectrometry (/xL2MS) is used to provide spatial resolution and identification of organic molecules across a meteorite sample. Tracking the chemical composition across the surface of the meteorite requires a full mass spectrum to be measured every 10 p,m across the surface. The molecules must be desorbed from the surface with minimal disruption to their chemical structure to prevent fragmentation so that the mass spectrum consists principally of parent ions. Ideally, the conventional electron bombardment ionisation technique can be replaced with an ionisation that is selective to the carbonaceous species of interest to simplify the mass spectrum. Most information will be obtained if small samples are used so that sensitivity levels should be lower than attomolar (10—18 M) fewer than 1000 molecules can be detected and above all it must be certain that the molecules came from the sample and are not introduced by the instrument itself. 

The results are reported of a study of plate-out in PVC extrusion carried out using several analytical techniques, including DSC, SEM-EDX, FTIR spectroscopy and laser ionisation mass spectrometry. A special die and calibrator unit developed to investigate plate-out are illustrated and the reproducibility of the method evaluated. The effects of water content and anti-plate-out additives, such as alumina and silica, on plate-out are discussed and mechanisms explaining the formation of plate-out are proposed. 11 refs. 

LIMS laser ionisation mass spectrometry lipid, lipidic neutral fat, e.g. the ester of fatty acids (monocarbonic acids) with glycerine fatty... 

An example of this is shown in Figure 15 for a poly(methyl methacrylate)/polystyrene laminate. Data from a 6 x 6 array of pyrolysis measurements were used to reconstruct images based upon the ion yield of the respective monomers. Unlike similar methods of chemical imaging (e.g. secondary ion mass spectrometry and laser ionisation mass spectrometry), the sample is examined under ambient conditions rather than high vacuum [167]. Three-dimensional tomographic imaging may also be considered by using the probe to ablate the surface. 

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... 

LDMS Laser desorption mass spectrometry desorption/ionisation... 

Experimental considerations Sample preparation and data evaluation are similar to membrane osmometry. Since there is no lower cut-off as in membrane osmometry, the method is very sensitive to low molar mass impurities like residual solvent and monomers. As a consequence, the method is more suitable for oligomers and short polymers with molar masses up to (M)n 50kg/mol. Today, vapour pressure osmometry faces strong competition from mass spectrometry techniques such as matrix-assisted laser desorption ionisation mass spectrometry (MALDI-MS) [20,21]. Nevertheless, vapour pressure osmometry still has advantages in cases where fragmentation issues or molar mass-dependent desorption and ionization probabilities come into play. 

Mass spectrometry is used to identify unknown compounds by means of their fragmentation pattern after electron impact. This pattern provides structural information. Mixtures of compounds must be separated by chromatography beforehand, e.g. gas chromatography/mass spectrometry (GC-MS) because fragments of different compounds may be superposed, thus making spectral interpretation complicated or impossible. To obtain complementary information about complex mixtures as a whole, it may be advantageous to have only one peak for each compound that corresponds to its molecular mass ([M]+). Even for thermally labile, nonvolatile compounds, this can be achieved by so-called soft desorption/ionisation techniques that evaporate and ionise the analytes without fragmentation, e.g. matrix-assisted laser desorption/ionisation mass spectrometry (MALDI-MS). 

Besides the well-established chromatographic/mass spectrometric or spectroscopic methods there is always a need for complementary methods for the study of organic materials from art objects. The application of laser desorption/ionisation mass spectrometry (LDI-MS) methods to such materials has been reported only sporadically [12, 45 48] however, it is apparently increasing in importance. After GALDI-MS had been applied to triterpenoid resins, as described in Section 5.2, this relatively simple method was evaluated for a wider range of binders and other organic substances used for the production or conservation of artwork. Reference substances as well as original samples from works of art were analysed. 

J.J. Boon, and T. Learner, Analytical Mass Spectrometry of Artists Acrylic Emulsion Paints by Direct Temperature Resolved Mass Spectrometry and Laser Desorption Ionisation Mass Spectrometry, J. Anal. Appl. Pyrol., 64, 327 344 (2002). 

Bunch, J., Clench, M. R., and Richards, D. S. (2004). Determination of pharmaceutical compounds in skin by imaging matrix-assisted laser desorption/ionisation mass spectrometry. Rapid Commun. Mass Spectrom. 18 3051-3060. 

Prideaux, B., Clench, M. R., Carolan, V. A., Morton, J., and Rajan-Sithamparanadarajah, B. (2005). Imaging matrix assisted laser desorption ionisation—mass spectrometry for the investigation of dermal absorption of chlorpyrifos. In Proceedings of the 53rd ASMS Conference on Mass Spectrometry and Allied Topics, San Antonio, TX. 

D. S. Ashton, C. R. Beddell, D. J. Cooper, and A. C. Lines, Determination of carbohydrate heterogeneity in the humanised antibody CAMPATH 1H by liquid chromatography and matrix-assisted laser desorption ionisation mass spectrometry, Anal. Chim. Acta, 306 (1995) 43 18. 

Ramendik [16] pointed to the possibilities of the creation and development of theoretical foundations based on mathematical modelling in elemental mass spectrometry after the creation of a plasma. For laser plasma mass spectrometry of geological RMs and a quasi-equilibrium approach based on atomisation and ionisation temperatures without relying on reference RMs materials, he claims to be able to arrive at average uncertainties for 40 elements totalling 20% [17]. This may not be ideal but it is a suitable accuracy for solving many practical analytical problems. 

MALDI-MS Matrix-assisted laser desorption/ionisation mass spectrometry... 

The two additives have heen identified hy matrix assisted laser desorption ionisation mass spectrometry (MALDI-MS) and attenuated total reflection infrared spectroscopy (ATR). 

Schrader, M., Jurgens, M., Hess, R., Schuiz-Knappe, P., Raida, M., Foessmann, W. G. (1997). Matrix-assisted laser desorption/ionisation mass spectrometry guided purification of human guanylin from blood ultrafiltrate. J. Chromatogr. A 776, 139-145. 

A recently introduced technique for the separation of larger molecules is matrix-assisted faser Resorption-ionisation mass spectrometry (MALDI-MS). Developed by Karas et al. [4, 5] in 1988, it has been successfully used to determine the mass of biomolecules up to 500.000 Da. This method is based on the principle that the dissolved specimen is mixed with a matrix, and then crystallizes. After drying, a laser pulse is directed onto the solid matrix to photo-excite the matrix material,resulting in desorption and soft ionisation of the analyte.The molar mass is then determined by the lime ef ilight (TOF). 

Kolarich D, Altmann F N-glycan analysis by matrix assisted laser desorption/ionisation mass spectrometry of electrophoretically separated non-mammalian proteins. Application to peanut allergen Ara h 1 and olive pollen alleigen Ole e 1. Anal Biochem 2000 285 64-75. 

Orsnes, H. andZenobi, R. (2001) Interfaces for on-line sample delivery for matrix-assisted laser desorption ionisation mass spectrometry. Chem. Soc. Rev. 30, 104-112. 

Larhrib, H. Wells, M.H. Rubinstein, M.H., et al. Characterization of PEGs using matrix-assisted laser desorption/ ionisation mass spectrometry and other related techniques. Int. J. Pharm. 1997, 14, 187-198. 

Laser Excited Atomic Fluorescence Spectrometry (LEAFS) (40, 41, 46-48), Thermal Ionisation Mass Spectrometry (TIMS) (6, 42, 43, 45, 49-53), Electrothermal Atomization Atomic Absorption Spectrometry (ETA-AAS) (24, 28, 54, 55), Differential Pulse Anodic Stripping Voltammetry (DPASV) (27, 49, 56, 57),... 

Since the 1980s a revolution in the use of mass spectrometry for biological analyses has occurred and continues today. A major reason for this development was the introduction of new ionisation techniques such as fast atom bombardment (FAB), plasma desorption (PD) and thermospray (TSP) permitting the production of gas phase ions from charged and polar biopolymers [7—10). It has reached a first culmination with the recent award of the 2002 Nobel prizes in chemistry to two scientists pioneering the development of electrospray-ionisation and laser desorption mass spectrometry, John Fenn and Kuichi Tanaka [11, 12]. 

Hunt, S. M., Sheil, M. M., and Derrick, P. J., Comparison of Electrospray Ionisation Mass Spectrometry with Matrix-assisted Laser Desorption Ionisation Mass Spectrometry and Size Exclusion Chromatography for the Characterisation of Polyester Resins, Eur. Mass Spectrom., 4, 475, 1998. 

Montaudo, G., Montaudo, M. S., Puglisi, C., Samperi, F., and Sepulchre, M., End-group Gharacterization of Poly(methylphenylsilane) by Alkali Metal Salts Doped MALDI-TOE Mass Spectra, Macromol. Chem. Phys., 197, 2615,1996. Weidner, St. and Kiihn, G., Chemical End-group Derivatization of Polyfethyl-eneglycol)-Investigation by Matrix-assisted Laser Desorption/Ionisation Mass Spectrometry, Rapid Comm. Mass. Spectrom., 10, 942,1996. 

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