David J. Heiler

Comparative studies of poly(dimethyl siloxanes) using automated GPC-MALDI-TOF MS and on-line GPC-ESI-TOF MS

In this study we compare on-line gel permeation chromatography (GPC) electrospray ionization (ESI) time-of-flight (TOF) mass spectrometry (MS) to automated GPC matrix assisted laser desorption ionization (MALDI) TOF MS for poly (dimethylsiloxane) (PDMS) analysis. Average mass values for a hydroxyl-terminated PDMS (OH-PDMS) sample were obtained and compared to traditional GPC that was calibrated with narrow polystyrene standards, by direct ESI and MALDI MS analysis, by a summation of mass spectra of all GPC fractions, and also by the recalibration method determined by both mass spectrometric methods. Quantitatively, the difference noted here between these hyphenated techniques is that GPC-ESI-TOF MS effectively reports the low-mass oligomers and underestimates the high-mass oligomers, while GPC-MALDI-TOF MS effectively reports the high-mass oligomers and underestimates the low-mass oligomers. In the GPC-ESI-TOF MS experiments, ion current suppression was observed in the high molecular weight region. The suppression effect was confirmed by repeatable sample runs and by injecting different PDMS samples. Higher chromatographic resolution was observed for GPC-ESI-TOF MS compared to GPC-MALDI-TOF MS. In fact, truly mono-disperse oligomers were observed in the low molecular weight range from GPC-ESI MS experiments.

Characterization of silicone rubber extracts using gel- permeation chromatography, matrix-assisted laser desorption/ionization mass spectrometry, electrospray ionization mass spectrometry, Fourier transform infrared spectroscopy and gas chromatography/mass spectrometry

Extracts from a silicone rubber product were characterized by gel-permeation chromatography (GPC), matrix-assisted laser desorption/ionization time-of-flight (MALDI-ToF) mass spectrometry, Fourier transform infrared spectroscopy (FT-IR), electrospray time-of-flight (ESI-ToF) mass spectrometry and gas chromatography/mass spectrometry (GC/MS). The extracted sample was determined to be a complex mixture with a molecular weight ranging from 200 to 210,000 Da as determined from GPC measurements. GPC fractions of the extract sample were further analyzed by MALDI-ToF mass spectrometry, ESI-ToF mass spectrometry, FT-IR spectroscopy and GC/MS. The extracted products were determined to be macrocyclic poly(dimethylsiloxane) oligomers. Two additives known as bis(2-ethylhexyl) adipate and bis(2-ethylhexyl) phthalate were observed in the extract.