MALDI-MS of Synthetic Polymers

The most important parameters that can be determined by MALDI are number-average molecular weight (MJ, weight-average molecular weight (M ), and the molecular weight distribution expressed as polydispersity PD) [119,182]  

Example Polystyrenes ranging from PS 2200 to PS 12500 form [M-t-metal] ions with Ag and Cu ions when silver or copper(I) salts are admixed to the sample preparation. In case of PS 12500, both metal ions were found to effect cationi- 

In addition, the determination of a polymer s endgroup(s) [183,184] and the analysis of random and block-copolymers [185,186] can be achieved by MALDI. However, care has to be taken when judging the MALDI spectra because of the mass-dependent desorption and detection characteristics of the experiment. In case of higher polydispersity (PD 1.1) high-mass ions are underestimated from MALDI spectra [106,182]. The current practice to deal with such samples is to fractionate them by gel permeation chromatography (GPQ [181] or size-exclusion chromatography (SEC) prior to MALDI analysis [182,187]. 

MALDI is the method of choice for the analysis of synthetic polymers because it usually provides solely intact and singly charged [62] quasimolecular ions over an essentially unlimited mass range. [22,23] While polar polymers such as poly(methylmethacrylate) (PMMA), [83,120] polyethylene glycol (PEG), [120,121] and others [79,122,123] readily form [M+H] or [M+alkali] ions, nonpolar polymers like polystyrene (PS) [99,100,105,106] or non-functionalized polymers like polyethylene (PE) [102,103] can only be cationized by transition metal ions in their l-t oxidation state. [99,100] The formation of evenly spaced oligomer ion series can also be employed to establish an internal mass calibration of a spectrum. [122] 

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