Desorption ionization cationization

The ProteinChip System from Ciphergen Biosystems uses patented SELDI (Surface-Enhanced Laser Desorption/Ionization) ProteinChip technology to rapidly perform the separation, detection, and analysis of proteins at the femtomole level directly from biological samples. ProteinChip Systems use ProteinChip Arrays which contain chemically (cationic, anionic, hydrophobic, hydrophilic, etc.) or biochemically (antibody, receptor, DNA, etc.) treated surfaces for specific interaction with proteins of interest. Selected washes create on-chip, high-resolution protein maps. This protein mass profile, or reten-tate map of the proteins bound to each of the ProteinChip Array surfaces, is quantitatively detected in minutes by the ProteinChip Reader. 

Several original papers must be mentioned that deal with mass spectrometric techniques which the numerous reviews do not comprise. Kaufmann and coworkers268,288 studied the mass spectrometric analysis of carotenoids and some of their fatty acid esters using matrix-assisted laser desorption/ionization (MALDI) mass spectrometry and its post-source-decay (PSD) variant. Some advantages concerning the thermal instability and limited solubility were discussed, but the fragmentation paths of the carotenoid cations were found to be essentially the same as those observed with conventional techniques. 

Rashidezadeh, H. Hung, K. Baochuan, G. Probing Polystyrene Cationization in Matrix-Assisted Laser/Desorption Ionization. Eur. Mass Spectrom. 1998,4,429-433. 

Keki, S., Deak, G., and Zsuga, M., Fragmentation study of rutin, a naturally occurring flavone glycoside cationized with different alkali metal ions, using post-source decay matrix-assisted laser desorption/ionization mass spectrometry, J. Mass Spectrom., 36, 1312, 2001. 

In initial work, a total of 17 different ILs were evaluated by the solvation parameter model [8]. Ten of these ILs were comprised of imidazolium or pyrolidinium cations paired with different anions. Many of these compounds represent the traditional class of IL solvents that have been used extensively in organic synthesis reactions or in other analytical uses. The remaining seven ILs consisted of substituted ammonium cations that have proven to be successful analyte matrices in matrix-assisted laser desorption ionization (MALDI) mass spectrometry [11]. 

E. Botek, J. L. Debrun, B. Hakim, and L. Morin-Allory, Attachment of alkali cations on beta-D-glucopyranose Matrix-assisted laser desorption/ionization time-of-flight studies and ah initio calculations, Rapid Commun. Mass Spectrom, 15 (2001) 273-276. 

The. V-pixvl function, when substituted with electron-donating groups, has also proved useful since the stabilized cations derived from this function are readily detected by mass spectrometry at the femtomolar level by either laser desorption ionization or MALDI techniques <2005EPP1506959, 2005SL2453>. The readily available sulfoxide derivatives also function as efficient mass-tags in mass spectrometry applications <2005CC3466>. 

Figure 10. Laser desorption/ionization time-of-flight mass spectra of La Li-BINOL complex in anionic (top) and cationic (bottom) modes.

MALDI-MS refers to matrix-assisted laser desorption-ionization mass spectroscopy, It is also called MALFI-TOF, because the mass spectrometer is a time-of-flight version. In this technique, the polymer is mixed with a molar excess of a salt, for cationization, and deposited on a probe surface. A UV laser is pulsed... 

Tn 1922 Adam (I) published the third paper in his extraordinary series on surface film structure. He observed that fatty acid monolayers greatly expanded on alkaline subphases. He also suggested that fatty acid anions desorbed or dissolved from the monolayer into the alkaline subphase. In 1933 he and Miller (2) showed that the composition of the subphase buffer significantly affected the monolayer thus palmitic and stearic acid monolayers were more condensed on 2N sodium hydroxide than on 2N potassium hydroxide. The expansion, desorption, and cation selectivity of ionizing monolayers are the subjects of this investigation. 

The almost endless possibilities of mass spectrometry have been increased by yet another hopeful variant SELDI (surface-enhanced laser desorption ionization). SELDI combines protein chips with a UV-MALDl-TOF. The chips are solid aluminum strips coated with cationic or anionic ion exchangers, with hydrophile or hydrophobic molecules. Chips with activated surfaces are also available. These bind proteins covalently via their amino groups and enable you to coat chips with antibodies or receptors as you need them. Every chip has eight coated holes with a diameter of 1 mm. You apply the sample into the holes. Part of the pro-teins/peptides is adsorbed. The remainder is washed off. The adsorbed proteins/peptides are transferred into matrix and can then be analyzed in the mass spectrometer (Figure 7.8). What can SELDI do better than MALDI ... 

T. J. R M. Naven and D. J. Harvey, Cationic derivatization of oligosaccharides with Girard s T reagent for improved performance in matrix-assisted laser desorption/ionization and electrospray mass spectrometry. Rap. Commun. Mass. Spectrom., 10 (1996) 829—834. 

Scrivens, J. H., Jackson, A. T, Yates, H. T., Green, M. R., Critchley, G., Brown, J., Bateman, R. H., Bowers, M. T., and Gidden, J., The effect of the variation of cation in the matrix-assisted laser desorption/ionization-collision induced dissociation (MALDI-CID) spectra of oligomeric systems, Int J. Mass Spectrom. Ion Processes, 165/166, 363, 1997. 

Knochenmuss, R., Lehmann, E., and Zenobi, R., Polymer Cationization in Matrix-assisted Laser Desorption/Ionization, Eur. Mass. Spectrom., 4, 421, 1998. 

Lloyd, P. M., Scrivener, E., Maloney, D. R., Haddleton, D. M., and Derrick, P. J., Cation Attachment to Synthetic Polymers in Matrix-Assisted Laser Desorption/ Ionization Mass Spectrometry, Polymer Preprint, 847, 1996. 

King, R. C., Goldschmidt, R., Xiong, Y., and Owens, K. G., Mechanistic Studies of the Cationization of Synthetic Polymers by Alkaly Metals in the Matrix-assisted Laser Desorption/Ionization Experiment. 43rd ASMS Conf. Mass Spectrom., Atlanta, GA, 1237, 1995. 

---