Investigation of Chromatographic Surface Viscosity Using Total Internal Reflection Fluorescence

Total internal reflection fluorescence (TIRF) spectroscopy was employed to determine the viscosity of planar chromatographic surfaces. Various n-alkyldimethylchlorosilanes were used to modify the surface of a UV-quartz plate, so as to obtain a covalently attached monomeric C 1 , C 3 , C 8 , or C 18 surface. TIRF anisotropy data of 1, 6-diphenylhexatriene (DPH) were collected on the unmodified and modified surfaces in the presence of overlaying solvents covering a range of viscosities. The results indicate that DPH adsorbs onto C 1 and C 3 , but clearly exhibits partitioning with the C 18 phase. The C 8 surface data indicate intermediate behavior between adsorption and partitioning. On the basis of these preliminary data, the estimated microviscosity of a planar C 18 surface is approximately 18 cP.