Bonded phases with hydrocarbonaceous ligates

As discussed by Minors in the first volume of this series (57), modern liipiid chromnlography employs bonded stationary phases not only with hydrocarbonaceous, but also with polar ligates, me bonded phases of intermediate polarity (7/5) can be used with either polar or nonpolar mobile phases. With a sufficiently polar eluent the technique falls into the category of RPC as this chromatographic method by defiiiition employs a mobile phase more polar than the stationary phase so that retention increases with decreasing polarity of eluites having similar molecular dimensions. 

Factors that influence the retentive powers and selectivity of such bonded phases include the surface concentrations of hydrodartenaceous ligates and free silanol groups. The thermodynamic aspectitm solute interactions with the hydrocarbonaceous ligates at the surface, which are hydrophobic interactions in the case of aqueous eluents, are discussed later in this chapter within the framework of the solvophobic theory. In practice, however, solute interactions with surface silanol which may be termed silanophilic interactions can also contribute ]to retention (71, 75, 93), particularly in the case of amino compounds. Consequently the retention mechanism may be different from that which would be ol served with an ideal nonpolar phase. Therefore, increasing attention is paid to the estimation of the concentration of accessible sianols and to their elimination from the surface of bonded phases. 

---