Mass spectroscopy desorption/ionisation

Mass spectroscopy [electron ionisation (El), chemical ionisation (Cl), electrospray ionisation (ESI), fast atom bombardment (FAB), matrix-associated laser desorption ionisation (MALDI), inductively coupled plasma-mass spectrmetry (ICP-MS, cf and ), etc]... 

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

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. 

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. 

A variety of laser techniques have been applied for direct analysis of additives in polymers. Table 3.1 shows the relation between various induced phenomena and proposed analytical methods, broadly classitied as laser spectroscopy and laser mass spectrometry. Some specific features for lasers are multiphoton absorption spectroscopy (based on the frequency dependency), multiphoton ionisation spectroscopy (with resonance enhancement) and laser mass spectrometries (laser wavelength and intensity dependency desorption/ionisation). 

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... 

Matrix Assisted Laser Desorption Ionisation Mass Spectroscopy... 

H.D. Beckey, Principles of Field Ionisation and Field Desorption Mass Spectroscopy, Pergamon Press, New York, NY, USA, 1977. 

Lattimer and co-workers [30] have applied mass spectroscopy to the determination of antioxidants and antiozonants in rubber vulcanisates. Direct thermal desorption was used with three different ionisation methods (electron impact, Cl, field ionisation (FI)). The vulcanisates were also examined by direct fast atom bombardment mass spectroscopy (FAB-MS) as a means for surface desorption/ionisation. Rubber extracts were examined directly by these four ionisation methods. Of the various vaporisation/ ionisation methods, it appears that FI is the most efficient for identifying organic additives in the rubber vulcanisates. 

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. 

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. 

---