MALDI-MS identification

Basic Protocol 3 MALDI-MS Identification of Flavonol Glycosides 11.5.3... 

Bhaisare ML, Abdelhamid HN, Wu B-S, Wu H-F. Rapid and direct MALDI-MS identification of pathogenic bacteria from blood using ionic liquid-modified magnetic nanoparticles (Fe304 Si02). J Mater Chem B. 2014 2(29) 4671-83. doi 10.1039/C4TB00528G. 

Applications MALDI-ToFMS is at its best as a rapid screening technique for quick identification of known additives. However, this screening is rendered slightly more complicated by the fact that MALDI-ToFMS spectra of pure additives and of additives in the presence of excess macromolecules are not always identical (matrix effect) [55]. For unknown additives, the relation MALDI-ToFMS spectrum-chemical structure is not easily established, and the use of FD or MALDI-MS/MS is then needed. As MALDI-MS shows a sensitivity difference for the various additives, it cannot easily quantify them unless the analytes are very similar. For differentiation of additives with the same mass number (e.g. Tinuvin 315 and Cyasorb UV3638 with m/z = 368) high resolution is required, as provided by delayed extraction MALDI-ToFMS. 

Each of the subsystems can, apart from the others, make a significant diagnostic contribution. For example, the instrumental cell isolation and sample handling component could be used with DNA-based or other non-MS systems for detection and/or identification. As another example, the principles underlying pattern drift compensation can apply to MALDI MS and even non-MS detection systems such as capillary GC of fatty acid methyl esters. 

The focus of this chapter is the development of a technique often called wholecell matrix-assisted laser desorption ionization (MALDI) time-of-flight (TOF) mass spectrometry (MS) or whole-cell MALDI-TOF MS. Some groups prefer to use terms such as intact or unprocessed rather than whole, but the intended meaning is the same regardless of which word is used. As noted in the first chapter of this book, there are many different methods for the analysis of bacteria. However, for the analysis of intact or unprocessed bacteria, whole-cell MALDI-TOF MS is the most commonly used approach. This method is very rapid. MALDI-TOF MS analysis of whole cells takes only minutes because the samples can be analyzed directly after collection from a bacterial culture suspension. Direct MALDI MS analysis of fungi or viruses is similar in approach1,2 but is not covered in this chapter. MALDI-TOF MS of whole cells was developed with very rapid identification or differentiation of bacteria in mind. The name (whole cell) should not be taken to imply that the cells are literally intact or whole. Rather, it should be taken to mean that the cells that have not been treated or processed in any way specifically for the removal or isolation of any cellular components from any others. In whole-cell analysis the cells have been manipulated only as necessary to... 

In developing algorithms for automated identification of bacterial samples using MALDI MS, it is important to consider only those reproducible peaks... 

Approximately 90% to 95% of whole-cell MALDI MS profiles are representative of the ribosomal proteins abundant in rapid growth whole cells. Although the identification of proteins, from whole bacterial cells, by MALDI-TOF MS analysis is ambiguous, at best, due to the low-mass accuracy and resolving power, several researchers realized that many of the observed... 

Stony Brook synthesized a photoreactive benzophenone containing inhibitor (39, Fig. 14) which efficiently labeled the active site of the enzyme. The photoinhibition was prevented by adding native Ras to the reaction mixture. That competition indicated that the labeling was specific at the active site. Peptide mapping of the labeled enzyme by HPLC, Edman sequencing and MALDI-MS allowed the identification of key amino acids in the substrate binding, as Asp-110 and Asp-112 in the a-subunit [126]. 

The literature contains numerous references to the use of MS/MS in the determination of new neuropeptides in identified cells of invertebrates (Bulau et al., 2004, for a recent example) and this technique is now being applied to in situ analysis of vertebrate tissues (Fournier et al., 2003). MS/MS is also used for studies of neuropeptide processing (Nilsson et al., 2001), pharmacokinetics of synthetic peptides (Mock et al., 2002), nonpeptide drug metabolism (Kamel et al., 2003), identification of peptides purified by immunoaffinity (Suresh Babu et al., 2004), and MALDI/MS/MS techniques adaptable to brain dialysis (Bogan and Agnes, 2004). 

G. Ekstrand, R. Kange, P. Andersson, S. Wallenberg A CD microlaboratory for improved protein identification by MALDI MS, in Proceedings of the 50th ASMS Conference on Mass Spectrometry and Allied Topics, Orlando, 2002, ThPA 004, 1558.pdf, available at www.gyros.com. 

Since its introduction some 20 years ago, MALDI-MS has been established as a standard technique for a large variety of applications within the field of bioanalyt-ical mass spectrometry, ranging from protein identification to enzyme activity screening. Quantitative analysis has long been a challenge, but, with the use of isotopically labelled standards, it is steadily obtaining more attention. 

MALDI-MS was developed for the analysis of nonvolatile samples and was heralded as an exciting new MS technique for the identification of materials with special use in the identification of polymers. It has fulfilled this promise to only a limited extent. While it has become a well-used and essential tool for biochemists in exploring mainly nucleic acids and proteins, it has been only sparsely employed by synthetic polymer chemists. This is because of lack of congruency between the requirements of MALDI-MS and most synthetic polymers. 

Classical MALDI-MS requires that the material should be soluble in a suitable solvent. A suitable solvent means a solvent that is sufficiently volatile to allow it to be evaporated prior to the procedure. Further, such a solvent should dissolve both the polymer and the matrix material. Finally, an ideal solvent will allow a decent level of polymer solubility, preferably a solubility of several percentage and greater. For most synthetic polymers, these qualifications are only approximately attained. Thus, traditional MALDI-MS has not achieved its possible position as a general use modern characterization tool for synthetic polymers. By comparison, MALDI-MS is extremely useful for many biopolymers where the polymers are soluble in water. It is also useful in the identification of synthetic polymers, such as PEO where the solubility requirements are fulfilled. Thus, for PEO we have determined the molecular weight distribution of a series of compounds with the separations in ion fragment mass 44 Da corresponding to CH2-CH2 units. 

Hofmann, S., Gluckmaim, M., Kausche, S., Schmidt, A., Corvey, C., Lichtenfels, R., Huber, C., Albrecht, C., Karas, M., and Herr, W., Rapid and sensitive identification of major histocompatibility complex class 1-associated tumor peptides by nano-LC MALDI MS/MS, Molecular and Cellular Proteomics 4(12), 1888-1897, 2005. 

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