MALDI matrices

El = electron ionization Cl = chemical ionization ES = electrospray APCI = atmospheric-pressure chemical ionization MALDI = matrix-assisted laser desorption ionization PT = plasma torch (isotope ratios) TI = thermal (surface) ionization (isotope ratios). 

MALDI. matrix-assisted laser desorption ionization... 

MALDI = matrix assisted laser desorption, ftms = Fourier transform mass spectrometry TOF = time of flight. 

MALDI Matrix Assisted Laser Desorption Ionization... 

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,... 

Figure 2.1 Mass spectrometric approach. Dl, direct inlet GC, gas chromatography HPLC, high performance liquid chromatography CZE, capillary zone electrophoresis El, electron ionization Cl, chemical ionization ESI, electrospray ionization DESI, desorption electrospray ionization APCI, atmospheric pressure chemical ionization MALDI, matrix assisted laser desorption ionization B, magnetic analyzer E, electrostatic analyzer...

Other MS based analytical approaches have occasionally been applied to ancient resin samples, in particular for paint varnishes. Such techniques include FABS (fast atom bombardment mass spectrometry) [35], MALDI (matrix assisted laser desorption-ionization mass spectrometry) and GALDI (graphite assisted laser desorption-ionization mass spectrometry) [36 38]. 

Also for MALDI, there is a special case worth mentioning. Surface-enhanced laser desorption/ionization (SELDI) is a technique that utilizes special sample plates [196, 197]. These have different modified surfaces, for example, hydrophobic, anionic, or antibody treated. Which type of surface to select depends on the application. After application of analyte the surface is washed according to a protocol leaving only the desired components on the target. Finally, a MALDI matrix is applied before analysis in the spectrometer. See Chapter 12 for an application example of SELDI. 

Name two commonly used MALDI matrix compounds. (3,5-dimethoxy-4-hydroxy-3-phenylacrylic acid, 2,5-dihydroxybenzoic acid... among others). 

Proteins and other large biomolecules can be analyzed using MALDI (matrix-assisted laser desorption and ionization) with TOF... 

MALDI matrix spectra are characterized by strong molecular and/or quasi-molecular ion signals accompanied by series of matrix (Ma) cluster ions and some more abundant fragment ions. [32] In positive-ion MALDI, [Man-hH]" cluster ions predominate, while [Ma -H] cluster ions are preferably formed in negative-ion MALDI. The principal ion series may be accompanied by [Ma H-alkali] ions and some fragments of minor intensity, e.g., [Ma H-H-H20]. In particular with aprotic matrices, radical ions may predominate. In addition, a continuous background is... 

For example, our preliminary MALDI MS studies employed a somewhat unconventional sample preparation approach in which the protein deposition step preceded the matrix deposition step. (In the conventional approach, the protein is co-deposited with the MALDI matrix solution.). .. Thus, in the first/next/colleclively group of experiments, we will explore different sample preparation methods to determine if other protocols also lead to an inverse relationship between surface-protein binding affinity and the MALDI ion signal. 

In the last years, ILs have been applied as matrices for matrix-assisted laser desorption/ionization (MALDI) MS [42], thus expanding the use of MALDI. In Ref. 38 the suitability of alkylammonium- and alkylimidazolium salts of a-cyano-4-hydroxycinnamic acid was investigated as a MALDI matrix and at the same time as the additive of BGE. The alkylammonium salt produced better separation of phenolic compounds than the alkylimidazolium salt. The investigation suggests that it is possible to synthesize ILs suitable for electrophoretic analysis as well as for online MALDI-MS analysis. 

Figure 14.1 Schematic view of a mass spectrometer. Its basic parts are ion source, mass analyzer, and detector. Selected principles realized in modern mass spectrometers are assigned El—electron impact. Cl—chemical ionization, FAB—fast atom bombardment, ESI—electrospray ionization, MALDI—matrix-assisted laser desorption/ionization. Different combinations of ion formation with mass separation can be realized.

Figure 14.7 MALDI spectra of the MALDI matrix DHB (upper) and the ionic liquid matrix formed by equimolar mixture of DHB and triethylamine (lower). The triethylammonium-cation is the only signal in the spectrum of the ILM, the signal corresponding to DHB (as well as adducts and fragments thereof) are suppressed in the ILM. (From Tholey, A. and Heinzle, E., Anal. Bioanal. Chem., 386, 24, 2006. With permission from Springer, Heidelberg, Germany.)...

In 1974, Comarisov and Marshall60 developed Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS). This technique allows mass spectrometric measurements at ultrahigh mass resolution (R = 100000-1000000), which is higher than that of any other type of mass spectrometer and has the highest mass accuracy at attomole detection limits. FTICR-MS is applied today together with soft ionization techniques, such as nano ESI (electrospray ionization) or MALDI (matrix assisted laser/desorption ionization) sources. 

MALDI Matrix-assisted Laser desorption/ionisation... 

Whether using FAB-MS, LSIMS, or MALDI, matrix ions might interfere with the... 

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