QUANTITATIVE TIME-OF-FLIGHT SECONDARY ION MASS-SPECTROMETRY OF A PERFLUORINATED POLYETHER

Quantitative determination of the molecular weight and composition of submicrogram quantities of a perfluorinated polyether (PFPE) supported on Ag and Si substrates was made from empirical relationships derived from the intensities of specific high-mass (greater-than-or-equal-to 800 amu) fragmentation ions from time-of-flight secondary ion mass spectrometry (TOF-SIMS) measurements. These relationships are explained in terms of simple concepts regarding the process of volatilization, fragmentation and ionization in TOF-SIMS. The results for both negative and positive ions are nearly independent of the substrate materials used, demonstrating that the high-mass fragmentation ions in TOF-SIMS may be useful generally for in situ quantitative analysis of PFPEs on non-specific substrates. This is an important difference between the TOF-SIMS fragmentation spectrum and the complementary TOF-SIMS cationized molecular ion spectrum, which requires special sample preparation and/or substrates. In order to interpret the quantitative information available in the TOF-SIMS fragment spectrum, it was absolutely necessary to characterize extensively the PFPE samples using NMR and TOF-SIMS Ag+-cationized molecular ion results. This characterization helped to demonstrate the power of TOF-SIMS to do quantitative analysis and led to additional insight concerning the SIMS ion-forming process for PFPE. This study represents one of the first attempts to make quantitative use of the high-mass fragment ion intensities in SIMS studies of polymers, and presents a method for confirming the origin of the mass peaks in the spectra.