Matrix-assisted laser-desorption ionization plate

The most discriminating technique for proving the identity and purity of analyte peak of a chromatogram, especially for analyzing biological samples and natural products, is by using online LC-UV/MS or GC-MS/FTIR methods [15]. Alternatively, one could use a combination of TLC and MS, where direct determination on the TLC plates is made by matrix-assisted laser desorption ionization mass spectrometry (MALDI MS) [16]. 

A CE run can also be spotted on a matrix assisted laser desorption ionization (MALDI) plate by using a probot microfraction collector by LC Packings. The matrix solution, 2 mg/mL... 

Matrix assisted laser desorption ionization time-of-flight (MALDI-TOE) mass spectrometry was carried out with a PerSeptive Biosystems Voyager-DE-RP MALDl-TOF mass spectrometer. A 337-nm UV nitrogen laser producing 3-ns pulses was used in the reflectron mode. The samples were prepared by mixing 10 pi of a 0.1 M HAc solution of the sample with 20 pi of a solution of 3 mg/1 a-cyano-4-hydroxy cinnamic acid in wafer. One pi of that solution was loaded on the gold-sample plate. 

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. 

J. Guittard, X. P. L. Hronowski, and C. E. Costello, Direct matrix-assisted laser desorption/ ionization mass spectrometric analysis of glycosphingolipids on thin layer chromatographic plates and transfer membranes, Rapid Commun. Mass Spectrom., 13 (1999) 1838-1849. 

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]. 

Matrix Assisted Laser Desorption Ionization-Mass Spectrometry (MALDI-MS) Mass spectra of native and denatured antibodies were obtained with a PerSeptive Biosystems (Farmingham, MA.) Voyager Elite mass spectrometer operated in the linear mode with a Laser Sciences Inc., 337 nm nitrogen laser. hAB-1 was denatured by boiling the sample in 1.0 M guanidine-HCl, 50 mM Tris pH 7.5 buffer. Native and denatured samples were diluted with 20 mM Tris, 10 mM octylglucoside (Tris/OG) pH 6.8 buffer prior to MALDl-MS analysis. Proteins were spotted on the sample plate as a sandwich between two layers of the matrix. The bottom layer consisted of 100 mM sinapinic acid in acetonitrile and the top layer consisted of 50 mM sinapinic acid in 30% acetonitrile / 70% H2O / 0.07% TFA. The m/z scale of the instrument was calibrated using a Hewlett-Packard protein standard mixture. 

Matrix-assisted laser desorption ionization (MALDI) is a frequently used ionization technique, but it is rarely used as an on-line detector. The sample stream is applied to a target plate, and it is allowed to cocrystallize with the matrix, which is subsequently desorbed, ionized with a laser, and analyzed in the MS. There has been attempts of combining FFF and MALDI, and for biomolecules, MALDI is a good ion source, due to the soft ionization with high efficiency and simple mass spectra, even for heavier molecules because the majority carry only single charge. 

AJ Nicola, AI Gusev, DM Hercules. Direct quantitative analysis from thin-layer chromatography plates using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. Appl Spectrosc 50 1479—1482, 1996. 

MALDI MCPs MO MPI MWNT matrix-assisted laser desorption/ionization multi-channel plates molecular orbital multi-photon ionization multiwalled carbon nanotube... 

FiCURE 4.3 Matrix-assisted laser desorption ionization source, (a) Gas phase ions are formed when the nitrogen laser produces photons at 337 nm that strike the solid matrix-analyte sample. The ions above the sample plate are accelerated to 25,000 eV of kinetic energy and fly through a stainless steel tube (not shown) for TOP m/z analysis, (b) Three commonly used matrix molecules for MALDI of peptides and proteins. 

Another new teehnology that shows promise as a high-throughput screening tool is FlashQuant. FlashQuant is a triple quadrupole MS/MS system that has a high-speed matrix-assisted laser desorption/ionization (MALDI) source. The MALDI souree ean provide for the very rapid assay of samples on a plate format. Beeause there is no ehromatography, the sample assay speed is about 6 s/sample (10 samples/min) this is 10—20 times a typical HPLC—MS/MS assay speed. The teehnique has potential for use in early in vitro assays that have simple matriees. At this time, it is too early to state whether or not this technique will be useful for EDM sereens. 

Moskovets, E., Chen, H.S., Pashkova, A., Rejtar, T., Andreev, V., and Karger, B.L. (2003) Closely spaced external standard a universal method of achieving 5 ppm mass accuracy over the entire MALDI plate in axial matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. Rapid Commun. 

A., Meisen, I., Vukelic, Z., Peter-Katalinic,)., Hfllenkamp, F., and Berkenkamp, S. (2005) Analysis of gangliosides directly from thin-layer chromatography plates by infrared matrix-assisted laser desorption/ ionization orthqional time-of-flight mass spectrometry with a glycerol matrix. Anal. Chem., 77, 4098-4107. 

Analysis of native milk oligosaccharides directly from thin-layer chromatography plates by matrix-assisted laser desorption/ionization orthogonal-time-of- flight mass spectrometry with a glycerol matrix. J. 

Amantonico, A., Urban, P.L., Zenobi, R. (2009) Facile Analysis of Metabolites by Capillary Electrophoresis Coupled to Matrix-assisted Laser Desorption/Ionization Mass Spectrometry Using Target Plates with Polysilazane Nanocoating and Grooves. Analyst 134 1536-1540. 

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