Molecular weight distribution methods mass spectrometry

ESI mass spectra of mixtures are difficult to interpret, because each component produces ions with many different charge states. The most direct and reliable method to solve this problem is to use high-resolution MS and calculate the charge states by measuring the spacing of the isotope peaks. ESI mass spectrometry of (polymeric) mixtures with broad molecular weight distribution benefits from a prior separation that reduces the polydispersity of the analyte. 

Field ionization mass spectrometry (FIMS) was applied to the different compound classes by Boduszynski et al. (1980). The FIMS molecular weight envelopes shown in Fig. 8 illustrate the similar but wide molecular weight distribution for each compound class. Furthermore, the FIMS molecular weight of about 1000 are considerably lower than those obtained by other methods in which intermolecular association may influence measured values. This is evident in Table IX by the comparison of VPO... 

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... 

MALDI mass spectrometry is an established technique in the biopolymer area, particularly useful for low-molecular-weight polymers. Not only does MALDI-MS provide a polymer molecular weight distribution, but for low-molecular-weight polymers the method can provide useful information regarding end-groups incorporated into the polymer from initiators or chain-transfer agents [56]. In many instances this fimctionaUty has a substantial impact on polymer performance. 

When new polymers are synthesized, their molecular characterization becomes imperative. NRL should continue to explore the newer methods of molecular characterization, including, for example, such methods as laser desorption mass spectrometry, which has been used to obtain molecular weight distributions for samples with molecules having molecular weights up to 10 grams per mole (g/mol). 

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