System constants of synthesized poly(methyl-3,3,3-trifluoropropyl) siloxanes

• Published in: Journal of Chromatography A 2005-12, Vol.1100 (2), p.208-217
• Main Authors: Lebrón-Aguilar, R., Quintanilla-López, J.E., Tello, A.M., Pérez-Parajón, J.M., Santiuste, J.M.
• Format: Article
• Language: English
• Subjects: Analytical chemistry; Chemistry; Chromatographic methods and physical methods associated with chromatography; Chromatography, Gas - instrumentation; Dimethylpolysiloxanes - chemical synthesis; Dimethylpolysiloxanes - chemistry; Exact sciences and technology; Gas chromatographic capillary columns; Gas chromatographic methods; Principal Component Analysis; Solvation parameter model; Specific retention volumes; System constants; Temperature; Trifluoropropyl siloxane stationary phases
• ISSN: 0021-9673
• DOI: 10.1016/j.chroma.2005.09.044

The method of solvation model has been applied to five poly (methyl-trifluoropropyl) siloxanes (TFPSXX) prepared in our laboratories, at five trifluoropropyl (TFP) group contents, XX = 0, 11.5, 26.3, 35.5 and 50.0%, at 80, 100, 120 and 140 °C. Previously, specific retention volumes of 60-odd solutes of varied polarities were measured upon each of these stationary phases within the above temperature range. Constant s prevails over all other constants, TFPSXX stationary phases showing strong dipole/induced dipole forces with the solutes, moderate acidity and no basicity at all. Constant e is zero in the stationary phase without TFP groups, but has negative low-medium values for the other fluorine contents, XX from 11.5 to 50.0%, hinting at repulsive forces, as expected. Normal values for constant l, decreasing from the less cohesive TFPS00 to the more cohesive TFPS50, were found. For each TFP content constants s, a and l show a negative temperature dependence, while constant e increases as temperature increases. Constant c also decreases with increasing temperature. At each temperature, constants s and a increase with increasing %TFP (or increasing stationary phase polarity), whereas constants e and l show the opposite trend, diminishing with increasing polarity of the stationary phase. Principal component analysis shows that the five stationary phases presented in this work conform a group with other earlier synthesized trifluoropropyl siloxanes and other fluorinated stationary phases taken from literature: VB-210, QF-1, DB-200, DB-210 and PFS6, showing the same selectivity which only the fluorine atom confers. A dendrogram of 38 stationary phases supports these results.