Atmospheric-Pressure MALDI

Atmospheric-pressure MALDI (AP-MALDI) is conceptually similar to normal MALDI except that it is performed ontside the source vacuum at atmospheric pressure [63,64]. Similar to other AP ion sources (e.g., ESI), orthogonal acceleration TOP, quadrupole ion trap, Unear ion trap (LIT), and FT-ICR instruments are ideal MS systems for conpUng with AP-MALDI. Ion gnides made of 

Surface-enhanced laser desorption/lonization (SELDI) is a novel alternative to conventional MALDI for the analysis of target compounds in a mixture [65,66]. It is a unique sample preparation platform that combines the concepts of liquid chromatography separation and MALDI analysis in one. In this approach, an analyte or a group of analytes are captured on a solid-phase chip via adsorption, partition, electrostatic interaction or affinity chromatography. A matrix is added to the solid surface next, and analyzed as usual by MALDI-TOF approach. 

Hydrophobic Cation exchange Anion exchange Metal affinity 

A new technique, known as material-enhanced laser desorption/ionization (MELDI), has become available for profiling proteins in complex mixtures [67], It uses derivatized carrier materials, such as cellulose, silica, poly(glycidyl methylacrylate/divinylbenzene), or diamond powder, to bind proteins from the sample. The carrier particles are derivatized with iminodiacetic acid (IDA) and loaded with ions to form [carrier-IDA-Cu +] complex, which is then added to the protein sample. The protein-bound carrier materials are spotted on the MALDI target, mixed with a MALDI matrix and analyzed by MALDI-TOF-MS. 

In atmospheric pressure MALDI (AP-MALDI) the MALDI process takes place under atmospheric pressure in dry nitrogen gas. The desorbed ions are then transferred into the vacuum of the mass analyzer by means of an atmospheric pressure ionization (API) interface which is typically provided by an electrospray ionization (ESI, Chap. 11) source. AP-MALDI was first presented in combination with an orthogonal acceleration TOE (oaTOF, Chap. 4.2.6) analyzer whae the original ESI ion source was modified to accommodate a sinple MALDI target plus laser instead of the ESI spray capillary [208]. AP-MALDI has also been adapted to a quadrupole ion trap (QIT, Chap. 4.5) [209] where an inproved design was realized by extending the heated transfer capillary of a Finnigan LCQ ion trap instru 

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Atmospheric pressure ionisation Atmospheric pressure MALDI Atmospheric pressure photo-ionisation Atmospheric pressure spray ionisation... 

Pribil, P. Patton, E. Black, G. Doroshenko, V. M. Fenselau, C. Rapid characterization of Bacillus spores targeting species-unique peptides produced with an atmospheric-pressure MALDI source. J. Mass Spectrom. 2005, 40,464-474. 

Atmospheric pressure MALDI (AP-MALDI) was introduced in 1998 by Laiko et al. [198, 199]. The advantage with the AP version of MALDI is the possibility of coupling... 

P. V. Tan, V. V. Laiko, and V. M. Doroshenko. Atmospheric Pressure MALDI with Pulsed Dynamic Focusing for High-Efficiency Transmission of Ions into a Mass Spectrometer. Anal. Chem., 76(2004) 2462-2469. 

Atmospheric pressure ionization mass spectrometers, 13 468 Atmospheric pressure chemical ionization (APCI) liquid chromatography, 4 625 Atmospheric Pressure MALDI, 15 658 Atmospheric stability, of organic semiconductors, 22 210... 

C. Fenselau, MALDI MS and Strategies for Protein Analysis, Anal. Chem. 1997,69, 661 A R. W. Nelson, D. Nedelkov, and K. A. Tubbs, Biomolecular Interaction Analysis Mass Spectrometery, AnaL Chem. 2000, 72, 405A J. J. Thomas, R. Bakhtiar, and G. Siuzdak, Mass Spectrometry in Viral Proteomics, Acc. Chem. Res. 2000,33, 179 A. P. Snyder, Interpreting Protein Mass Spectra (Washington, DC American Chemical Society, 2000) S. C. Moyer and R. J. Cotter, Atmospheric Pressure MALDI, Anal. Chem. 2002, 74, 469A. 

In 2000, various developments in the field of MALDI led to the advent of new methods such as the atmospheric pressure MALDI (AP-MALDI) source. This method combines the atmospheric pressure (AP) source and MALDI [45-47]. Indeed, this source produces ions of analytes under normal atmospheric pressure conditions from analyte-doped matrix microcrystals by irradiating these crystals with laser pulses. 

Tan, P.V., Laiko, V.V., Doroshenko, V.M. (2004) Atmospheric pressure MALDI with pulsed dynamic focusing for high-efficiency transmission of ions into a mass spectrometer. Anal. Chem. 76,2462-2469. 

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]. 

J.M. Daniel, V.V. Laiko, V.M. Doroshenko, R. Zenobi, Interfacing LC with atmospheric-pressure MALDI-MS, Anal. Bioanal. Chem., 383 (2005) 895. 

S.C. Moyer, R.J. Cotter, A.S. Woods, Fragmentation of phosphopeptides by atmospheric-pressure MALDI and ESI ion trap mass spectrometry, J. Am. Soc. Mass Spectrom., 13(2002)274. 

Moyer S, Cotter R Atmospheric pressure MALDI. Anal Chem 2002 74 469A-76A. 

Wei, H. Nolkrantz, K. Powell, D.H. Woods, J.H. Ko, M.-C. Kennedy, R.T. Electrospray Sample Deposition for Matrix-Assisted Laser Desorption/lonization (MALDI) and Atmospheric Pressure MALDI Mass Spectrometry With Attomole Detection Limits, Rapid Commun. Mass Spectrom. 18, 1193-1200 (2004). 

Moyer, S.C. and Cotter, R.J., Atmospheric pressure MALDI, Anal. Chem., 74(17), 469A, 2002. 

The rapid vaporization of macromolecules from biological samples prevents, or minimizes, their dissociation and fragmentation and thus provides a way to obtain molecular and structural information. Also, MALDI provides a way of producing different types of cationized molecular ions with LP, NaL CuL and Ag+, in addition to the protonated species usually formed in atmospheric pressure ionization processes. The most serious drawbacks of using MALDI are the price of a suitable laser and the complexity and limited applicability to certain types of solid samples. Although early studies were made with MALDI-MS with the ion source region under vacuum, the demonstration of atmospheric pressure MALDI with MS encouraged the development of MALDI-IMS. 

Some examples of studies with MALDI and IMS include the use of MALDI to generate sodiated parent ions of a number of oligosaccharides without fragmentation and cationized forms of bradykinin. Cross sections of the ions were obtained and compared with predictions made by molecular mechanics or molecular dynamics calculations. Comparison of MALDI/IM/TOF-MS with MALDI/IM/MS analysis yielded results similar to that by nanoelectrospray MS. Dipeptides and biogenic amines were analyzed with a system that consisted of an atmospheric pressure MALDI source, an IMS, and an orthogonal TOF-MS, and sensitivity was improved when a localized CD source was added. ... 

Doroshenko, V.M. Laiko, V.V. Taranenko, N.I. Berkout, V.D. Lee, H.S. Recent developments in atmospheric pressure MALDI mass spectrometry. Int. J. Mass Spectwm. 

M. Cui, M. A. McCooeye, C. Fraser, and Z. Mester, Quantitation of lysergic acid diethyl amide in urine using atmospheric pressure MALDI ion trap mass spectrometry. Anal Chem. 76, 7143-7148 (2004). 

In atmospheric pressure MALDI (ap-MALDI), the sample is ionized outside the vacuum system and ions are captured through a small orifice, usually into an ion-trap mass spectrometer. Its advantage appears to be a considerable amount of rapid collisional cooling of the ions by the high atmospheric pressure, leading to stabilization of sensitive compounds. On the other hand, some compounds, such as carbohydrates, appear to suffer increased fragmentation under these conditions. 

Trimpin, S., Inutan, E.D., Herath, T.N., and McEwen, C.N. (2010) Laserspray ionization, a new atmospheric pressure MALDI method for producing highly charged gas-phase ions of peptides and proteins directly from solid solutions. Mol. Cell. Proteomics, 9, 352-357. 

Atmospheric pressure MALDI-Fourier transform mass spectrometry. 

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