Matrix-assisted laser desorption molecular-weight distribution

The molecular weights and molecular weight distributions (MWD) of phenolic oligomers have been evaluated using gel permeation chromatography (GPC),23,24 NMR spectroscopy,25 vapor pressure osmometry (VPO),26 intrinsic viscosity,27 and more recently matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS).28... 

For the quick characterisation of polydisperse surfactants with relative high molecular weight distributions matrix-assisted laser desorption/ionisation (MALDI)-time of flight (TOF)-MS represented an interesting alternative since low mass compounds did not interfere with the mass spectrometric detection of the compounds of interest. For example, the mass spectrum of C12-APG (Fig. 2.7.8) exhibited equally spaced signals with Am/z 162 corresponding to sodiated adduct ions of the mono- (m/z 371) to heptaglucosides (m/z 1343) [7]. 

Matrix-Assisted Laser Desorption/lonization Time-of-liight Mass Spectrometry (MALDI-TOF MS, PerSeptive Biosystems Voyager-DE STR) was used to characterize the molecular weight distribution and the number average molecular weight (M ) of the poly(methacrylic acid) (PMAA) degradation products as described elsewhere [25]. 

Finally, another method commonly used to characterize these copolymeric materials is that of matrix-assisted laser desorption ionization-time of flight (MALDI-TOF) mass spectrometry. When using this technique, it is possible to investigate the molecular weight distributions, end groups, and polymer constitution of low-molecular-weight samples [63], MALDI-TOF may also provide vital... 

Cryoscopy and ebulioscopy can be used for the measurement of Mn for polymers in a similar way to the application on smaller molecules, and the procedure is used mainly when Mn < 2 10. I LDI-MS (matrix-assisted laser desorption ionization-mass spectroscopy) allows the measurement of both Mn and M , as well as the molecular weight distribution, which indicates the variation of w, (weight fraction of the component i ), as a function of M,. 

O Conner, P. B., Duursma, M. C., van Rooij, G. J., Heeren, R. M. A., and Boon, J. J., "Correction of Time-of-Flight Shifted Polymeric Molecular Weight Distributions in Matrix-Assisted Laser Desorption/Ionization Fomier Transform Mass Spectrometry," Anal. Chem., 69, 2751-2755,1997. 

Spickermann, J., Martin, K., Rader, H. J., Mullen, K., Schlaad, H., Muller, A. H. E., and Kruger, R.-R, Quantitative Analysis of Broad Molecular Weight Distributions Obtained by Matrix-assisted Laser Desorption/Ionization Time-of-flight Mass Spectrometry, Eur. Mass Spectrom., 2, 161, 1996. 

Guo, B., Chen, H., and Liu, R. X., Observation of Varying Molecular Weight Distributions in Matrix-assisted Laser Desorption/Ionization lime-of-Flight Analysis of Polymethyl Methacrylate, Rapid Comm. Mass. Spectrom., 11, 781,... 

Vitalini, D., Mineo, P, and Scamporrino, E., Further Application of a Procedure for Molecular Weight and Molecular Weight Distribution Measurement of Polydisperse Polymers from Their Matrix-Assisted Laser Desorption/Ionization Time-of-Flight Mass Spectra, Macromolecules, 30, 5285,1997. 

Zammit, M. D., Davis, T. R, and Haddleton, D. M., Determination of the Propagation Rate Coefficient (kp) and Termination Mode in the Free-Radical Polymerization of Methyl Methacrylate, Employing Matrix-Assisted Laser Desorption Ionization Time-of-Flight Mass Spectrometry for Molecular Weight Distribution Anal5 is, Macromolecules, 29, 492, 1996. 

In recent years, the technology of mass spectroscopy has been well developed. The matrix-assisted Laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) can be applied to measure the molecular weights of macromolecules (up to one million Dalton) due to its high sensitivity and its wide response range. In combinatiOTi with the distribution of fragment lengths, it can be used to characterize those bio- and synthetic macromolecules with complicated molecular architectures. 

J.J. (1997) Correction of time-of-flight shifted polymeric molecular weight distributions in matrix-assisted laser desorption/ionization Fourier transform mass spectrometry. Anal. Chem., 69,... 

Matrix assisted laser desorption ionization (MALDI) is a frequently used ionization technique, but it is rarely used as an online detector. The sample stream is appUed to a target plate, and it is allowed to cocrystallize with the matrix, which is subsequently desorbed, ionized with a lasCT, and analyzed in the MS. MALDI/TOF has been successfully used to determine molecular weight distributions of fractions collected after thermal FFF separation of polydis-pCTse polymers. MALDI is a good ion source, due to the soft ionization with high effrciency and simple mass spectra, even for heavier molecules, since the m ority carry only a single charge. 

Laser desorption generates high mass ions by irradiating a solid with a pulsed laser beam. In the case of matrix-assisted laser desorption, a solid mixture of an analyte is dissolved in a suitable matrix compound and the laser pulse desorbs and indirectly ionizes the analyte molecules. The selection of appropriate MALDI matrix, cationization salt, sample concentration, and sample preparation technique are critical success factors for obtaining a reliable mass spectrum that influence the polymer distribution. An alternative technique used to eliminate matrix and cationization salt effects is direct LDI, which is generally used for polymer samples with relatively low molecular weights. 

The use of matrix-assisted laser desorption ionization/time of flight (MALDI-TOF) to characterize low-molecular-weight copolymers has also been reported by the Penczek research group. They used MALDI-TOF to obtain a precise characterization of the molecular weight distribution of polymer (both PCL and PLA) obtained... 

H. Schlaad, A.H.E. Muller Quantitative analysis of broad molecular weight distributions obtained by matrix-assisted laser desorption/ionisa-tion thiie-of-flight mass spectrometry. Eur. Mass Spectrom. 2, 161 (1996)... 

Among them, MS has become a valuable tool in studying polymer structure, composition, molecular weight distribution (MWD), and other important physical quantities [2-5]. Different MS techniques have been employed, with different degree of applicability and success, in providing comprehensive quantitative information on the sample analyzed. Traditional approaches such as ionization techniques [2, 5-10] or modern ones such as matrix-assisted laser desorption ionization (MALDl) MS [4, 11-13] are used to obtain structural and compositional information. 

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