The results of fast atom bombardment (FAB), time-of-flight secondary ion mass spectrometry (ToF-SIMS), matrix-assisted laser desorption/ionization (MALD/I), electrospray ionization (ESI), and field desorption (FD) analyses of ethoxylated oligomers of 2,4,7,9-tetramethyl-5-decyne-4,7-diol (Surfynol(®) 104) were compared.Each of these desorption mass spectrometry (MS) techniques can produce spectra of unfragmented cationized oligomers. From the observed ion series we calculate average molecular weight information. We have compared the results of mass spectrometric analyses of a series of ethoxylated Surfynol surfactants. Our data indicate that FAB, ToF-SIMS, MALDI/I, and ESI produce similar results for the lower molecular weight species, but that as the average molecular weight increases FAB and SIMS produce slightly lower results than MALD/I and FD. This could be due to increased fragmentation. ESI produced a result similar to FAB and SIMS for the highest average molecular weight material. Further experiments compare the mass spectral results with gas chromatographic quantitative data. Although gas chromatography is not expected to accurately analyze the higher mass oligomers, we observe significant differences in intensities of the short-chain oligomers (especially the 0- and 1-mers) when compared to the desorption mass spectrometer results. These differences may reflect poor cationization efficiency for very short oligomer chains in the mass spectrometric analyses.
The effect of metal cationization on the molecular weight distribution (MWD) of an ethoxylated polymer, Surfynol 465 (S465), is investigated by time-of-flight secondary ion mass spectrometry (ToF-SIMS) and a hybrid theoretical method combining ab initio density functional theory and molecular mechanics. The MWDs generated from sodium and from silver-cationized oligomers of S465 were measured by ToF-SIMS. The structure and bonding of the cationized complexes were calculated. The results suggest that upon cationization, the metal atoms are chelated by oxygen atoms and, in the case of Ag + , by the π-orbitals of the C-C triple bond. Although the binding energy of both Na + and Ag + with the Surfynol molecules is very high for sufficiently long ethoxylate side chains, strong bonding preference is given to Ag + over Na + due to the orbital interaction between Ag + and the Surfynol oligomer via 4d-π* and 5s-π overlap and the ion-dipole interaction between the cations and the oxygen atoms in the ethoxylate chains with Na + being of more ionic character. The theoretical results suggest that a minimum ethoxylate chain length is required for Na + chelation and that in the high molecular weight region both cations will bind with the Surfynol oligomers strongly, consistent with our experimental observations. We demonstrate that ToF-SIMS is an effective technique for measuring the molecular weight distribution of a low molecular weight oligomer series.
The determination of trans isomer content in partially hydrogenated vegetable oils is important in the characterization of fats and oils in the food industry. Current methods for characterization include gas chromatography and infrared spectroscopy of samples captured off-line. The determination of trans isomer content during the hydrogenation process has the potential to improve process productivity and quality control to meet the stringent requirements of oil producers. Raman spectroscopy was evaluated in comparison to infrared spectroscopy as a method for quantitatively determining the cis and trans isomer content in partially hydrogenated vegetable oils. Both infrared and Raman principal component regression (PCR) calibrations accurately modeled the GC values (AOCSOfficial Method Ce 1f-96) for cis and trans content. In addition, the cis and trans isomer content of canola oil could be determined after the results from the IR and Raman calibration methods for soybean oil were corrected for slope and offset. Raman spectroscopy possesses unique advantages and shows promise as a method for rapid in situ analysis.
The development of cluster primary ion sources such as Aun+, Bin+, SF5+, C60+, and Arn+ has been an exciting advancement in SIMS analysis. Relative to atomic primary ion sources, cluster ion sources provide higher secondary ion yields. Furthermore, C60+ and Arn+ impart significantly less chemical damage to the sample thus enabling molecular depth profiling. Molecular depth profiling using cluster primary ion sources is routinely used to characterize a wide range of commercially important materials, including organic light emitting diode, biomaterials and pharmaceuticals, adhesives, and architectural paints and coatings. This paper highlights the application of time of flight secondary ion mass spectrometry (ToF-SIMS) to study contact lenses and acrylic-based paints. In the first application, ToF-SIMS was used to investigate the surface composition of two commercial contact lenses. Lens material I is composed of 2-hydroxy-ethyl methacrylate (HEMA) and glycerol methacrylate while lens material II is composed of HEMA and 2-methacryloxyethyl phosphorylcholine cross-linked with ethyleneglycol dimethacrylate. The ToF-SIMS data confirm the presence of the 2-methacryloxyethyl phosphorylcholine on the surface of lens material II. ToF-SIMS was also used to characterize a HEMA-based contact lens which had been worn for about 4 weeks. The analysis reveals the presence of N-containing species, fatty acids, phosphorylcholine, and dioctyldecyl dimethyl ammonium. Arn+ gas cluster ion beams (GCIB) depth profiling indicates the N-containing species, the fatty acids, and the dioctyldecyl dimethyl ammonium are concentrated at the surface. In the second application, a combination of O2+ and Arn+ GCIB depth profiling was used to study the pigment levels in acrylic-based paints. The O2+ beam was used to profile into the bulk of the dried paint film and Arn+ gas cluster beam was then used to remove the damaged material. ToF-SIMS analysis of the crater bottom reveals differences in pigment levels. The combined O2+ and Arn+ GCIB depth profiling is an effective way of characterizing materials composed of both organic and inorganic components.
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