MALDI interface

FT-ICR mass spectrometers take advantage of ion-cyclotron resonance to select and detect ions. This analyzer can be used with both ESI and MALDI interfaces. Their particular advantages are their sensitivity, extreme mass resolution, and mass accuracy. The latter allows for the determination of the empirical formulae of compounds under 1000 Da. As far as we know, this analyzer has not been applied to flavonoids. 

Matrix-assisted laser desorption ionization is another ionization mode used for MS analysis. Enzymatically digested peptides have been studied using a 90-well microchip constmcted in a MALDI plate format (see Figure 7.41). Peptide digestion was initiated in the MALDI interface where the peptide hormone, adreno-corticotropin (ACTH) was mixed with the enzyme carboxypeptidase Y. The mixing process was self-activated in the vacuum conditions. Subsequent TOF MS analysis produced kinetic information of the peptide digestion reaction [820]. 

Most of the currently applied LC-MALDI interfaces use off-line spot deposition and a number of commercial instruments are available (Mukhopadhyay 2005). Compared to on-line techniques, this interface type is technically less demanding but only careful adjustment guarantees optimal performance. 

Next to conventional (vacuum) MALDI, atmospheric-pressure MALDI interfaces have been described, especially to enable MS-MS on MALDI-generated ions by ion-trap and (J-TOF instmments [145-146]. Atmospheric-pressure MALDI sources are commercially available from all major instrument manufacturers. First results on-line LC-atmospheric-pressure MALDI were reported as well [147]. 

Atmospheric pressure chemical ionization (APCI) Matrix-assisted laser desorption (MALDI) Interfaces to HPLC... 

In addition, since ions are analyzed in packets, TOF MS has a natural compatibility with the pulsed ion release of MALDI interfaces. If there is interest in a given m/z value, the pulsing frequencies can be adjusted to increase the duty cycle and the sensitivity by about one order of magnitude (lower micromolar range). 

In one of the most complete microfluidic systems developed for mass spectrometry applications to date, Gustafsson et al. [12] developed a MALDI interface for compact disk (CD)-based microfluidics, a technology in which reactions and separations are powered by centrifugal forces on a spinning device (CD Lab-on-a-Chip). Figure 3b demmistrates the operation of an individual analysis region (each CD contains 96 such regions). The sample is loaded (A) and then washed and eluted from a reversed-phase colunm (B). Finally, the sample is co-crystaUized with... 

Many excellent reviews on the development, instrumentation and applications of LC-MS can be found in the literature [560-563]. Niessen [440] has recently reviewed interface technology and application of mass analysers in LC-MS. Column selection and operating conditions for LC-MS have been reviewed [564]. A guide to LC-MS has recently appeared [565]. Voress [535] has described electrospray instrumentation, Niessen [562] reviewed API, and others [566,567] have reviewed LC-PB-MS. For thermospray ionisation in MS, see refs [568,569]. Nielen and Buytenhuys [570] have discussed the potentials of LC-ESI-ToFMS and LC-MALDI-ToFMS. Miniaturisation (reduction of column i.d.) in LC-MS was recently critically evaluated [571]. LC-MS/MS was also reviewed [572]. Various books on LC-MS have appeared [164,433,434,573-575], some dealing specifically with selected ionisation modes, such as CF-FAB-MS [576] or API-MS [577],... 

The introduction and eventual commercialization of matrix-assisted laser desorption/ionization (MALDI) and electrospray (ESI) allowed biomarker status to be extended to proteins in 1996.15"17 With a few exceptions, ESI has been used in conjunction with extractions and high-pressure liquid chromatography (UPLC) interfaced with mass spectrometry. MALDI, on the other hand, has been widely adapted for rapid analysis of intact organisms, supported by bioinformatics.1819... 

Chen, H.S., Rejtar, T., Andreev, V., Moskovets, E., Karger, B.L. (2005). High-speed, high-resolution monolithic capillary LC-MALDI MS using an off-line continuous deposition interface for proteomic analysis. Anal. Chem. 77, 2323-2331. 

To resolve the linear oligomer fractions, Weidner et al. (2004) proposed an alternative approach. He used the combination of LCCC and MALDI-TOF to identify the different functionalities. Weidner performed a separation according to chemical composition by LCCC, and used a spray interface (LC-Transform from LabConnections) to deposit the chromatographic fractions on a MALDI-TOF target. In the second step, each individual... 

Shimma S, Furuta M, Ichimura K. Direct MS/MS analysis in mammalian tissue sections using MALDI-QIT-TOFMS and chemical inkjet technology. Surf. Interface Anal. 2006 38 1712-1714. 

Sinz, A., Kalkhof, S., and Ihling, C. (2005) Mapping protein interfaces by a trifunctional cross-linker combined with MALDI-TOF and ESI-FTICR mass spectrometry. /. Am. Soc. Mass Spectrom. 16(12), 1921-1931. 

Offline-surface mediated approach Collect effluent from multiple LCs on surface place surface in MS interface use fast, surface-mediated ionization methods such as MALDI, DESI, etc. to sample effluents... 

The mass-selective instability mode of operation permits the selection and trapping of all ions created over a specified period with subsequent ejection to the detector.26 Ions with different m/z values can be confined within the ion trap and scanned singly by application of voltages that destabilize the orbits of the ions and eject them to the detector. Ion trap instruments interface readily with liquid chromatography, ESI,15 and MALDI.27 The motions of the ions and the dampening gas (e.g., helium) concentrate around the middle of the ion trap, thereby diminishing ion loss through collisions with electrodes. 

Time-of-flight mass spectrometers are interfaced with MALDI and electrospray ion sources. For proteomic applications they are most often interfaced with MALDI (Fig. 3). All ions from the ion source are accelerated to the same energy and then are left to drift in a field-free region. 

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