Matrix-assisted laser desorption/ionization atmospheric pressure-MALDI

DGE a AC AMS APCI API AP-MALDI APPI ASAP BIRD c CAD CE CF CF-FAB Cl CID cw CZE Da DAPCI DART DC DE DESI DIOS DTIMS EC ECD El ELDI EM ESI ETD eV f FAB FAIMS FD FI FT FTICR two-dimensional gel electrophoresis atto, 10 18 alternating current accelerator mass spectrometry atmospheric pressure chemical ionization atmospheric pressure ionization atmospheric pressure matrix-assisted laser desorption/ionization atmospheric pressure photoionization atmospheric-pressure solids analysis probe blackbody infrared radiative dissociation centi, 10-2 collision-activated dissociation capillary electrophoresis continuous flow continuous flow fast atom bombardment chemical ionization collision-induced dissociation continuous wave capillary zone electrophoresis dalton desorption atmospheric pressure chemical ionization direct analysis in real time direct current delayed extraction desorption electrospray ionization desorption/ionization on silicon drift tube ion mobility spectrometry electrochromatography electron capture dissociation electron ionization electrospray-assisted laser desorption/ionization electron multiplier electrospray ionization electron transfer dissociation electron volt femto, 1CT15 fast atom bombardment field asymmetric waveform ion mobility spectrometry field desorption field ionization Fourier transform Fourier transform ion cyclotron resonance... 

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). 

Moyor, S. C. Marzilli, L. A. Woods, A. S. Laiko, V. V. Doroshenko, V. M. Cotter, R. J. Atmospheric pressure matrix-assisted laser desorption/ionization (AP MALDI) on a quadrupole ion trap mass spectrometer. Int. I. Mass Spectrom. 2003, 226,133-150. 

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...

In contrast to the other ion sources, the MALDI source may operate under high vacuum or under atmospheric pressure. In the latter case the acronym AP-MALDI (atmospheric pressure matrix assisted laser desorption ionization) is used. 

Atmospheric pressure matrix-assisted laser desorption/ ionization AP- MALDI Photon induced desorption/ ionization Nonvolatile molecular ions Soft method Large molecules... 

Analytes must be liberated from their associated solvent molecules as well as be ionized to allow mass separation. Several ionization methods enable ion production from the condensed phase and have been used for the coupling of CE to MS. Among them, atmospheric pressure ionization (API) methods, matrix-assisted laser desorption/ionization (MALDI), and inductively coupled plasma (ICP) ionization are mainly used. API techniques are undoubtedly the most widespread ionization sources and cover different analyte polarity ranges. 

Figure A.3A.1 Flow chart illustrating the selection of a suitable ionization technique for the mass spectrometric analysis of a sample. Abbreviations APCI, atmospheric pressure chemical ionization Cl, chemical ionization El, electron impact FAB, fast atom bombardment MALDI, matrix-assisted laser desorption/ionization.

In direct introduction the sample can be introduced via a sample probe or plate through a vacuum lock, and can subsequently be ionized via El, Cl or matrix-assisted laser desorption ionization (MALDI see Section 2.4). Alternatively, the sample can be introduced as a liquid stream into an ion source at atmospheric pressure, after which it is subjected to electrospray ionization (ESI see Section 2.3). Direct injection does not offer any form of sample separation. 

Technological advances of ion-trap mass spectrometers are the ultrahigh-resolution Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) and the recently released technique, the Orbitrap Fourier transform mass spectrometry (Hu et al., 2005), which enable the determination of molecular formulae with a high mass resolution and mass accuracy in mixtures. Today these ion-trap mass spectrometers are most frequently coupled with atmospheric pressure ionization (API) techniques such as electrospray ionization (ESI) (e.g., Fievre et al., 1997 Qian et al., 2001 Kujawinski et al., 2002 Llewelyn et al., 2002 Stenson et al., 2002,2003 Fard et al., 2003) or matrix-assisted laser desorption/ionization (MALDI) (e.g., Solouki et al.,... 

Strege summarized the technique of high-performance liquid chromatography-electrospray ionization mass spectrometry (HPLC-ESI-MS) in dereplication of natural products. In contrast to earlier electron impact ionization (El), ESI technique is applicable to virtually any ion in solution with a soft ionization process. A comparison of ESI with fast atom bombardment (FAB), matrix assisted laser desorption ionization (MALDI), atmospheric pressure chemical ionization (APCI) and other techniques demonstrates its superior sensitivity, compatibility and reliability when coupled with HPLC [51]. 

Earlier methods of ionization applied to carotenoids, including electron impact (El), chemical ionization (Cl), a particle beam interface with El or Cl, and continuous-flow fast atom bombardment (CF-FAB), have been comprehensively reviewed elsewhere (van Breemen, 1996, 1997 Pajkovic and van Breemen, 2005). These techniques have generally been replaced by softer ionization techniques like electrospray ionization (ESI) and atmospheric pressure chemical ionization (APCI), and more recently atmospheric pressure photoionization (APPI). It should be noted that ESI, APCI, and APPI can be used as ionization methods with a direct infusion of an analyte in solution (i.e. not interfaced with an HPLC system), or as the interface between the HPEC and the MS. In contrast, matrix-assisted laser desorption ionization (MALDI) cannot be used directly with HPEC. 

A variety of MS formats are widely accepted and applied in the pharmaceutical industry. The specific MS application is often defined by the sample introduction technique. The pharmaceutical applications highlighted in this article feature two types of sample introduction techniques dynamic and static. Dynamic sample introduction involves the use of high-performance liquid chromatography (HPLC) on-line with MS. The resulting liquid chromatography/mass spectrometry (LC/MS) format provides unique and enabling capabilities for pharmaceutical analysis. The electrospray ionization (ESI) and atmospheric pressure chemical ionization (APCI) modes are the most widely used. Static sample introduction techniques primarily use matrix-assisted laser desorption/ionization (MALDI). ... 

Fig. 1 Schematic representation of a mass spectrometer depicting its main components and the different modes used. Abbreviations DIP direct insertion probe DEP direct exposure probe GC gas chromatography LC liquid chromatography CE capillary chromatography TEC thin-layer chromatography FEE field-flow fractionation APCI atmospheric pressure ionization El electron impact Cl chemical ionization FAB fast-atom bombardment PD plasma desorption MALDI matrix-assisted laser desorption ionization ED laser desorption TSP thermospray ESI electron spray ionization HSI hypherthermal surface ionization Q quadropole QQQ triple quadropole TOE time-of-fiight FTMS Fourier transform mass spectrometer IT ion trap EM electrom multiplier PM photomultiplier ICR ion cyclotron resonance.

Atmospheric pressure chemical ionization (APCI) Matrix-assisted laser desorption ionization (MALDI) Direct analysis in real time (DART)... 

Typically, MALDl has been performed under low pressure conditions (ca 10 Torr). In recent years, intermediate pressure (IP, 10 to 1 Torr) [10,12-14] and atmospheric pressure (AP) MALDl [15,16] systems have been developed to analyze more labile molecules and for tissue analysis [10]. Atmospheric pressure matrix-assisted laser desorption/ionization (AP-MALDl) offers the ability to couple a MALDl source to most commercial instruments, including quadrupole ion traps, because the source uses existing ion optics and vacuum transfer lines of commercial instruments to introduce the ions generated by MALDL A brief discussion of IP-MALDI with ion trap technology is presented, but the primary focus is on the instrumentation aspect of ion trap technology, in particular linear ion trap technology, for direct tissue analysis and imaging MS studies. 

Mass spectrometry is an analytical technique that can determine precisely the atomic or the molecular weight of atoms or molecules once they have been ionized. There are four key elements in mass spectrometer the sample introduction, the source where ionization occurs, the mass analyzer, and the detector. Mass spectrometry can analyze many different types of samples that range from solid, liquid, or gases. First, the molecules have to be ionized either under vacuum or at atmospheric pressure. Depending on the ionization technique, either molecular ions (M ) with an odd electron number or protonated ions ([M + H] with an even electron number are formed in the positive mode and M , M or ([M - H] in the negative mode. Ionization techniques are often classified into soft ionization, where little or no fragmentation occurs, and hard ionization, where fragmentation is extensive. Electrospray ionization (ESI) and matrix-assisted laser desorption ionization (MALDI) are... 

The successful on-line interfacing of several ion sources has made them dominant players in quantitative analyses using mass spectrometry. These include electron ionization (El) and chemical ionization (Cl) both coupled to GC, and the atmospheric pressure ionization (API) methods of atmospheric pressure chemical ionization (APCI) atmospheric pressure photoionization (APPI), and electrospray ionization (ESI) coupled to LC. In addition, matrix assisted laser desorption ionization (MALDI) is seeing increased application in off-line LC/MS applications. 

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