DEGRADATION AND SELECTIVE DESORPTION OF POLYMER CAN CAUSE UNCERTAINTYIN MALDI (MATRIX-ASSISTED LASER-DESORPTION IONIZATION) MEASUREMENTS

This paper compares the analysis of the molecular weight distribution of a poly(methyl methacrylate) (PMMA) sample by gel permeation chromat ography (GPC) and by matrix-assisted laser desorption ionisation (MALD I) mass spectrometry. The results show that the MALDI technique may be producing MW distributions that are not representative of the sample as a whole. It is evident that the laser radiation used in MALDI cause s degradation of the polymer structure, and this results in a MW distr ibution erroneously skewed towards lower MW. In addition, there is pre ferential desorption of lower molecular weight species, which results in the progressive skewing of the MW distribution towards higher MW wi th successive laser pulses. It is also shown that the matrix used in t he MALDI analysis is important in obtaining well-resolved mass spectra .