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 C1, C3, C-8, or C18 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 C1 and C3, but clearly exhibits partitioning with the C18 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 C18 surface is approximately 18 cP.