Matrix Assisted Laser Desorption Ionisation Mass Spectroscopy

2 Matrix Assisted Laser Desorption Ionisation Mass Spectroscopy 

Theoretical studies on matrix assisted laser desorption ionisation (MALDI) have been carried out by several workers [64-70]. 

In most of the combined MALDI-MS and ion exclusion chromatographic 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 [71], in which the two units are interfaced via a robotic interface. This technique was applied to studies of PS, polymethylmethacrylate (PMMA), and butyl(methacrylate-methylmethacrylate) copolymers. Mehl and co-workers [72] combined ion exclusion with MALDI-MS to provide accurate molecular weight determinations on polyether and polyester PU soft blocks. 

Dry MALDI sample preparation methods have recently been introduced to help 

The key to MALDI experiments is the matrix. In each experiment the matrix has four vital roles that must be accomplished to produce ions intimacy, absorption, desorption, and ionisation. 

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Dwyer [7] combined SEC and matrix assisted laser desorption ionisation - mass spectroscopy (MALDI-MS) to provide an insight into the structure and MWD of polymers. He showed that there are a number of factors that can influence results. 

The two additives have heen identified hy matrix assisted laser desorption ionisation mass spectrometry (MALDI-MS) and attenuated total reflection infrared spectroscopy (ATR). 

Instrumentation used for polymer oxidative stability (Chapter 11) includes, thermogravimetric analysis, differential scanning calorimetry, evolved gas analysis, infrared spectroscopy and ESR spectroscopy, matrix assisted laser desorption/ionisation mass spectrometry and imaging chemiluminescence is included. 

Matrix-assisted laser desorption/ionisation - time-of-flight - mass spectroscopy... 

Li, C.-Z., Herod, A.A., John, R, Johnson, C.A.F., Parker, J.E., Smith, G.P, Humphrey, R, Chapman, J.R., Rahman, M.,Kinghorn,R.R.F.,Kandiyoti,R. (1994) Characterisation of kerogens by matrix assisted laser desorption ionisation (MALDI) mass spectroscopy. Rapid Commun. Mass Spectrom., 8,823-828. 

Frequently, in work carried out to attempt to elucidate the microstructure of polymers and copolymers, it is found necessary to employ not one physical analytical technique, but a range of such techniques. The literature abounds in examples of this need. Judging by the number of papers published, three of the most useful and commonly used techniques are combinations of Fourier transform infrared spectroscopy (FTIR) or infrared (IR) spectroscopy and matrix assisted laser desorption-ionisation time-of-flight (MALDI-TOF) mass spectrometry with nuclear magnetic resonance spectroscopy or photon magnetic resonance spectroscopy. 

Kassalainen and Williams [135] coupled thermal field flow fractionation (ThFFF) and matrix-assisted laser desorption/ionisation time-of-flight mass spectroscopy (MALDI-ToF-MS) to yield a powerful combination of techniques for the analysis of polydisperse PS. ThFFF high selectivity and sensitivity to chemical composition were used to separate polydisperse polymers and polymer mixtures into the narrow polydispersity and homogeneous chemical composition fractions essential for MAT.DT-ToF-MS analyses. On the other hand, because it is possible to measure directly using MALDI-ToF-MS, it alleviates the need for polymer standards for ThFFF. Kassalainen and Williams [135] address the coupling of ThFFF and MALDI-ToF-MS and identify compatibility issues. Optimum conditions were determined and developed to maximise the capabilities of the combined technique. Depending on the polymer and the method of matrix-assisted laser desorption/ionisation (MALDI) sample deposition, fractions from 1-10 ThFFF runs were combined for MALDI-ToF-MS analysis. Binary solvents are used to enhance ThFFF retention and resolution of low (<15 kDa) polymers, and methods developed to allow routine MALDI-ToF-MS analyses of PS polymers up to 575 kDa. Overall, the compatibility of the two techniques was extended from several kilodaltons to several hundred kDa. Polymer... 

Montaudo and co-workers [10] studied the distribution of polymethyl acrylate-polybutylene adipate. Matrix assisted laser desorption ionisation - time of flight mass spectroscopy (MALDI) allows desorption and ionisation of very large molecules, even in complex mixtures. However, molar mass estimates provided by MALDI-ToE for synthetic polymers agree with the values obtained by conventional techniques only in the case of samples with a narrow molar mass distribution (MMD). However, when polydisperse polymer samples are fractionated by analytical SEC, they yield fractions with very narrow distributions which, when analysed by MALDI, are found to give mass spectra with molar mass values in excellent agreement with those obtained by conventional techniques. 

An review is given of the use of matrix-assisted laser desorption/ionisation time-of flight (MALDI TOF) mass spectroscopy to determine MWDs and structures of synthetic organic polymers, including the ion desorption mechanism, synthetic polymer analysis, molecular weight analysis, and its use in calibration of GPC profiles. 30 refs. 

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