MALDI-MS

Advances in methods used in the structural characterisation of redox-active polymers will aid in developing structure/property relationships and in guiding synthetic efforts. MALDI-MS analysis has proved to be a powerful structural characterisation tool for biopolymers. The application of MALDI-MS to synthetic polymers has been primarily limited to polar or polarisable polymers that can be protonated or can form salt/metal adducts. Electron transfer matrices for MALDI-MS of small, non-polar, redox-active analytes have been evaluated and it was found that anthracene and terthiophene are effective MALDI matrices for these analytes and assist in producing analyte molecular ions (not protonated molecules). Thus, non-polar, redox-active polymers might also be similarly ionised. 

Combined MALDI-MS and ion exclusion chromatographic techniques. In most of these techniques described in the literature the MALDI is not directly coupled off-line with the ion exclusion column. An exception is that of the work of Esser and co-workers [281], in which the two units are interfaced via a robotic interface. This technique was applied to studies of PS, PMMA, and butyl(methacrylate-methylmethacrylate) copolymers. Mehl and co-workers [282] combined ion exclusion with MALDI-MS to provide accurate molecular weight determinations on polyether and polyester polyurethane soft blocks. 

Other applications in which the two techniques are not connected in line mainly include the determination of molecular weights of copolymers of MMA, butyl acrylate styrene, and maleic anhydride [283, 284], cyclic PS [285-288], thiophene-phenylene copolymers [289], methacryloxypropyltrimethoxy silane [290], various copolymers [291], PEG [287], polyetherimide photooxidation products [292], polyester-polyurethane [293], biodegradable polymers [294], and polyethylene-propylene oxide-ethylene oxide triblock polymers [295]. 

Theoretical studies using ToF MALDI MS have been reported by various workers [326-330]. 

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Matrix-assisted laser desorption mass spectrometry (MALDI-MS) is, after electrospray ionization (ESI), the second most commonly used method for ionization of biomolecules in mass spectrometry. Samples are mixed with a UV-absorbing matrix substance and are air-dried on a metal target. Ionization and desorption of intact molecular ions are performed using a UV laser pulse. 

Hapten density, and also the common positions where haptens are bound, can also be estimated by cyanogen bromide or enzymatic cleavage of the protein and either MALDI-MS or separation of the components by reversed-phase ion-pair chromatography and electrospray or electrospray time-of-flight (TOF) analysis. 

The extraordinary complexity of human genes and their products has encouraged the development of extremely high-resolution analytical methods.75 Capillary electrophoresis is competitive with slab gel methods, with resolution up to the order of about 1,000 base pairs for sequencing, sizing, and detection of mutation. Reversed phase HPLC is useful for restriction digest mapping and MALDI-MS up to about 1000 base pairs. 

Dai, Y., Whittal R.M., and Li, L., Two-layer sample preparation a method for MALDI-MS analysis of complex peptide and protein mixtures, Anal. Chem., 71, 1087, 1999. 

Principles and Characteristics Problems connected with sample preparation, ionisation and detector efficiency can lead to errors in the quantitation of mass averages and MWD in the case of ESI-MS and MALDI-MS. Coupling of SEC with MS makes it possible to overcome these difficulties. SEC-MS has developed since the early 1990s. Two methods are currently outstanding on-line SEC-ESI-MS (QMS or FTMS) and semi on-line SEC-MALDI-ToFMS [709],... 

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. 

Figure 9.8 UV MALDI-MS spectrum of a mixture of polymer additives. After Jackson et al. [57]. Reprinted from A.T. Jackson et al., Rapid Communications in Mass Spectrometry, 10, 1449-1458 (1996). Copyright 1996 John Wiley Sons, Ltd. Reproduced with permission...

Bundy, J. Fenselau, C. Lectin-based affinity capture for MALDI-MS analysis of bacteria. Anal. Chem. 1999, 71,1460-1463. 

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... 

Most often proteins are the bacterial biopolymers studied using MALDI MS either from fractions or whole cells. They are not the only isolated cellular biopolymers studied by MALDI, nor the first. Very soon after the introduction of MALDI there were a few reports of the analysis of bacterial RNA or DNA from bacterial fractions. One of the first applications of MALDI to bacteria fractions involved analysis of RNA isolated from E. coli,4 Other studies included analysis of PCR-amplified DNA,5 6 DNA related to repair mechanisms7 and posttranscriptional modification of bacterial RNA.8 While most MALDI studies involve the use of UV lasers, IR MALDI has been reported for the analysis of double stranded DNA from restriction enzyme digested DNA plasmids, also isolated from E. coli.9... 

Harris, W. A. Reilly, J. R On-probe digestion of bacterial proteins for MALDI-MS. Anal. Chem. 2002, 74, 4410 1416. 

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