ORIENTATIONAL DYNAMICS OF A HYDROPHOBIC GUEST IN A CHROMATOGRAPHIC STATIONARY PHASE - EFFECT OF WETTING BY ALCOHOL

The orientational distribution of the alkyl chains of a C18 chromatographic surface was sensed indirectly from the orientational distribution of a long hydrophobic probe, 1,4-bis(o-methylstyryl)benzene. Frequency-domain fluorescence anisotropy measurements were used to determine the orientation and reorientation of the fluorescent probe. When pure water is in contact with the C18 surface, the orientational distribution of the probe is centered close to the plane of the surface. The effects of two different wetting solvents were explored: 20% methanol and 5% 1-propanol, When the C18 surface is in contact with either of these, there is little change In the orientational distribution of the probe.