A mixture of linear and cyclic methylsiloxanes was analysed to characterize the different types of siloxane structures using gas chromatography (GC), mass spectrometry (MS) and Fourier transform infrared (FT-IR) spectroscopy. Siloxane structures are formed by hydrolysis of dimethyldichlorosilane under controlled conditions in technical applications. In the presence of methyltrichlorosilane or even trimethylchlorosilane, linear polydimethylsiloxanes and mono-, bi- or polycyclic methylsiloxanes are synthesized depending on the reaction conditions. The main structural units are (CH3)3SiO1, (CH3)2SiO and (CH3)SiO3. GC-MS may provide molecular mass information, but it is not able to identify isomeric structures, which are also formed in lower quantities by the mentioned reactions. Coupling GC with FT-IR enables the determination of group frequencies to assign specific structures. Thus, combination of GC with MS and FT-IR may be used in elucidating complex cyclosiloxane compounds. FT-IR measurements were performed with a Tracer unit.
A series of 2-functional 1,3-dioxa-2,4,7-trisilacycloheptanes was synthesized and characterized by means of 29Si NMR spectroscopy, gas chromatography, high performance liquid chromatography and gas chromatography-mass spectrometry. The signals were assigned to the various configurational isomers. This assignment was confirmed by independent synthesis of individual isomers. The sequence of the NMR signals of the all-cis and trans-trans isomers required for the determination of stereochemistry was found to be the same as that of the respective cyclotrisiloxanes.
Untersuchungen von Ozonreaktionen an Squalen als Modellsubstanz mittels MALDI/MS, GC/MS und GC/FTIR
(1996)
Supercritical fluid chromatography in combination with mass spectrometry is used for determining cyclic siloxanes beside linear methyl and hydroxyl ''end-capped'' siloxanes. Electron impact ionisation and chemical ionisation techniques are utilized for identifying cyclic siloxanes in technical silicone oils and silicone rubber. Ammonia as reagent gas is preferred in the higher-molecular-mass range. Matrix-assisted laser-desorption ionisation mass spectrometry can be useful as a supplementary method for characterizing smaller amounts of both cyclic and linear siloxanes as well as silanols in the higher-molecular-mass range.