Determination of molecular mass distribution of silicone oils by supercritical fluid chromatography, matrix-assisted laser desorption ionization time-of-flight mass spectrometry and their off-line combination

Silicone oil samples were characterized by supercritical fluid chromatograp hy (SFC), matrix-assisted laser desorption ionization-time-of-flight mass s pectrometry (MALDI-TOF MS), and their off-line combination. SFC was used to separate samples of silicone oils on micropacked capillary columns. The fr actions for the identification studies were obtained from SFC runs at defin ed time intervals, when the restrictor was pulled out from the chromatograp hic flame ionization detector (FID) and inserted into a,glass vial with ace tone. MALDI-TOF MS was used for the identification of individual oligomers in the fractions separated. The molecular mass distributions determined bas ed on SFC and MALDI-TOF MS measurements were compared. From this comparison , it follows that the results are in good agreement. However, certain diffe rences were observed: MALDI-TOF MS was capable of detecting somewhat larger oligomers than the SFC-FID, but the lower molecular mass oligomers were no t present in the MALDI spectra. Differences in the region of lower molecula r masses can be explained by evaporation of the more volatile low molecular mass oligomers resulting from heating of the sample during the MALDI-TOF M S measurements as a result of the absorption of the laser shot energy. The fact that no high mass discrimination effects of the MALDI-TOF MS measureme nts, compared with SFC, were observed is very promising for further applica tions of MALDI-TOF MS in characterizing synthetic polymers of moderate poly dispersity. Copyright (C) 2001 John Wiley & Sons, Ltd.