A series of solvatochromic dyes has been used to probe the solid/solution interface of Cis bonded silica in mobile-phase mixtures consisting of methanol and water and acetonitrile and water. Chromatographic capacity factors (k) were measured in order to determine the fraction of dye sorbed at the surface. An adaptive Kalman filter has been used to resolve the spectrum of the surface-phase dye from that due to dye in the adjacent solution. Values for the Kamlet-Taft dipolarity/ polarizability x* parameter for octadecylsilica in contact with the methanol/water mobile phase ranged from 0.72 to 0.75, indicating that the stationary phase is considerably more polar than bulk alkane solutions. The interfacial values for x* and a (the Kamlet-Taft hydrogen bond acidity parameter) support the hypothesis that the chemistry and solvation of the interphase region is strongly influenced by the presence of residual surface silanol groups.Reversed-phase liquid chromatography (RPLC) is a commonly used method for the separation of a wide variety of analytes. The application of RPLC involves the use of a relatively nonpolar stationary phase such as octadecyl silica, and a more polar mobile phase, such as water mixed with various organic solvents. From a practical viewpoint, RPLC is an extremely valuable technique. At the same time, the chemistry of the stationary phase (the interphase region)* 1 23456is complex and has not been completely characterized.The characterization of the interphase region using spectroscopic probes has, thus far, been limited to the use of fluorescent probe molecules. These methods have revealed information regarding the polarity of the solvated surface2,3 and have provided some of the first evidence that the chemistry and properties of the stationary phase are dependent upon interactions with mobile-phase components.2-6 Some common fluorescent probes that have been used are pyrene, n-propanedansylamide, and n-decanedansylamide.2-6 One limitation of these fluorescent probes is that they are relatively nonpolar and may only sorb to specific regions of the stationary phase. In addition, they do not allow specific interactions, such as hydrogen bonding, dipolar, and dispersion, to be identified and only give an indication of the overall

Neither location nor configuration affects the primary patency of AVGs. Aspirin alone is not inferior to aspirin and clopidogrel. Further prospective studies may be warranted to establish a consensus regarding medications and patency with AVGs.

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