Matrix Assisted Laser Desorption/Ionisation

MALDl Matrix-assisted laser desorption/ionisation MD Molecular dynamics... 

MALDI-TOF MS Matrix-Assisted Laser Desorption Ionisation... 

Fast atom bombardment (FAB) Plasma desorption (PD) Liquid secondary-ion mass spectrometry (LSIMS) Thermospray (TSP)/plasmaspray (PSP) Electrohydrodynamic ionisation (EHI) Multiphoton ionisation (MPI) Atmospheric pressure chemical ionisation (APCI) Electrospray ionisation (ESI) Ion spray (ISP) Matrix-assisted laser desorption/ionisation (MALDI) Atmospheric pressure photoionisation (APPI) Triple quadrupole (QQQ) Four sector (EBEB) Hybrid (EBQQ) Hybrid (EB-ToF, Q-ToF) Tandem ToF-ToF Photomultiplier... 

Matrix-assisted laser desorption ionisation (MALDI) MH+ (M - H) ToF, IT, FTMS Polar and some nonpolar biopolymers, synthetic polymers >250000... 

As evident from Scheme 7.13, most modern ionisation techniques have been used for TLC-MS, and no single ionisation method is used exclusively with TLC-MS. Various ionisation methods may be applied that avoid the need to evaporate the sample into an El or Cl source these are based in particular on sputtering (FAB, SIMS) or laser desorption. Several sputtering methods of ionisation do not require the use of a liquid matrix, e.g. TLC-SIMS [797], Recent developments include the use of matrix-assisted laser desorption ionisation (MALDI) and surface-assisted laser desorption ionisation (SALDI). It is obvious that TLC-MS is complemented with TLC-MS11 [800] and TLC-HRMS techniques. Table 7.82 lists the general characteristics of TLC-MS. 

Figure 3.14. Schematic diagram of the scanning microprobe matrix-assisted laser desorption ionisation (SMALDI) mass spectrometer. (Spengler and Hubert 2002.)...

SMALDI scanning microprobe matrix-assisted laser desorption ionisation... 

Saenz, A. J. Petersen, C. E. Valentine, N. Gantt, S. L. Karman, K. H. Kingsley, M. T. Wahl, K. L. Reproducibility of matrix-assisted laser desorption/ionisation time-of-flight mass spectrometry for replicate bacterial culture analysis. Rapid Comm. Mass Spectrom. 1999,13,1585-1585. 

Bright, J. J. Claydon, M. A. Soufian, M. Gordon, D. B. Rapid typing of bacteria using matrix-assisted laser desorption ionisation time-of-flight mass spectrometry and pattern recognition software. J. Microbiol. Meth. 2002, 48,127-138. 

Domin, M. A. Welham, K. J. Ashton, D. S. The effect of solvent and matrix combinations on the analysis of bacteria by matrix-assisted laser desorption/ ionisation time-of-flight mass spectrometry. Rapid Comm. Mass Spectrom. 1999, 13, 222-226. 

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. 

Other types of atmospheric pressure ionisation detectors are available including APPI (photon ionisation) and MALDI (matrix-assisted laser desorption ionisation). More conventional detection systems for LC include UV absorption, fluorescence and evaporative light scattering. Developments in column packings,... 

S.T. Hsiao, M.C. Tseng, Y.R. Chen and G.R. Her, Analysis of polymer additives by matrix-assisted laser desorption ionisation/time of flight mass spectrometer using delayed extraction and collision induced dissociation, J. Chinese Chem. Soc., 48 (2001) 1017-1027. 

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). 

M.J. Dale, R. Knochenmuss, and R. Zenobi, Two phase Matrix assisted Laser Desorption/ Ionisation Matrix Selection and Sample Pretreatment for Complex Anionic Analytes, Rapid Commun. Mass Spectrom., 11, 136 142 (1997). 

F. Hihenkamp and M. Karas. Matrix-Assisted Laser Desorption/Ionisation, an Experience. hit. J. Mass Spectrom., 200(2000) 71-77. 

For the quick characterisation of polydisperse surfactants with relative high molecular weight distributions matrix-assisted laser desorption/ionisation (MALDI)-time of flight (TOF)-MS represented an interesting alternative since low mass compounds did not interfere with the mass spectrometric detection of the compounds of interest. For example, the mass spectrum of C12-APG (Fig. 2.7.8) exhibited equally spaced signals with Am/z 162 corresponding to sodiated adduct ions of the mono- (m/z 371) to heptaglucosides (m/z 1343) [7]. 

Matrix assisted laser desorption ionisation (MALDI) and ESI-MS spectra of non-ionic surfactant blends of AE obtained after positive ionisation were compared [28]. Both the ionisation procedures, which produce [M + Na]+ ion clusters, were very useful for this purpose, but the ESI spectra generated were more complex, whereas MALDI ionisation led to simpler spectra that can be interpreted more easily [28]. 

For the characterisation of the biodegradation intermediates of C12-LAS, metabolised in pure culture by an a-proteobacterium, Cook and co-workers [23] used matrix-assisted laser desorption/ionisation (MALDI)-time of flight (TOF)-MS as a complementary tool to HPLC with diode array detection and 1H-nuclear magnetic resonance. The dominating signal in the spectrum at m/z 271 and 293 were assigned to the ions [M - H] and [M - 2H + Na]- of C6-SPC. Of minor intensity were the ions with m/z 285 and 299, interpreted to be the deprotonated molecular ions of C7- and C8-SPC, respectively. 

While fast atom bombardment (FAB) [66] and TSI [25] built up the basis for a substance-specific analysis of the low-volatile surfactants within the late 1980s and early 1990s, these techniques nowadays have been replaced successfully by the API methods [22], ESI and APCI, and matrix assisted laser desorption ionisation (MALDI). In the analyses of anionic surfactants, the negative ionisation mode can be applied in FIA-MS and LC-MS providing a more selective determination for these types of compounds than other analytical approaches. Application of positive ionisation to anionics of ethoxylate type compounds led to the abstraction of the anionic moiety in the molecule while the alkyl or alkylaryl ethoxylate moiety is ionised in the form of AE or APEO ions. Identification of most anionic surfactants by MS-MS was observed to be more complicated than the identification of non-ionic surfactants. Product ion spectra often suffer from a reduced number of negative product ions and, in addition, product ions that are observed are less characteristic than positively generated product ions of non-ionics. The most important obstacle in the identification and quantification of surfactants and their metabolites, however, is the lack of commercially available standards. The problems with identification will be aggravated by an absence of universally applicable product ion libraries. 

Martin, R. L. Branda, E. L. Analysis of high mass peptides using a novel matrix-assisted laser desorption/ ionisation quadrupole ion trap time-of-flight mass spectrometer. Rapid Commun. Mass Spectrom. 2003, 17, 1358-1365. 

Ferret, C., Pezet, R., and Tabacchi, R., Fractionation of grape tannins and analysis by matrix-assisted laser desorption/ionisation time-of-flight mass spectrometry, Phytochem. Anal, 14, 202,... 

Fig. 4.5.8 Examples for structures and molecular masses of 2-aminobenzamide (2-AB)-labelled oligosaccharide moieties derived from serum transferrin. Values below the oligosaccharide structures indicate the expected masses (in Da) by matrix-assisted laser desorption ionisation - time of flight analysis.

Below we report methodological studies based upon HPLC, GC/FID, GC-MS, LC-MS, matrix-assisted laser desorption ionisation coupled with time-of-flight mass spectrometry (MALDI-ToF/MS), CE, proton nuclear magnetic resonance ( I INMR), RIA and enzymatic colorimetric techniques. 

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. 

Owen, S. J., Meier, F. S., Brombacher, S., and Volmer, D. A. (2003). Increasing sensitivity and decreasing spot size using an inexpensive, removable hydrophobic coating for matrix-assisted laser desorption/ionisation plates. Rapid Commun. Mass Spectrom. 17 2439-2449. 

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. 

C. S. Creaser, J. C. Reynolds, and D. J. Harvey, Structural analysis of oligosaccharides by atmospheric pressure matrix-assisted laser desorption/ionisation quadrupole ion trap mass spectrometry, Rapid Commun. Mass Spectrom., 16 (2002) 176-194. 

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