HPLC Column and Stationary Phases

The way to achieve HPLC is to return to packed columns, but to implement them with support particle and stationary-phase coating dimensions much smaller than those of packed column GC. Typically, one employs spherical silica particles of uniform diameters (monodisperse) in the range of 1.7-10 im. The interstitial spaces between the tightly packed spheres will be of similar dimension. Unlike the much larger support particles in packed colunm GC, these LC particles often 

Each LC-phase molecule is bonded to its solid support surface but is less often cross-linked. 

The HPLC phase is so thin that it is not a fully randomized fluid, like a GC polymer coating. 

Usually, it is impossible, due to steric hindrance or increasing crowding, to attach a molecule (like the -0-Si-(CH3)2CigH37 group) to every free silanol bonding site on the silica surface. 

These unreacted silanol sites lie closer to the mobile phase than in GC and can easily act as active sites degrading the chromatography as described in Section 11.4. 

---

The column is the heart of the chromatographic system and it is the only device where actual separation of the analyte mixture takes place. Detailed discussion of HPLC columns and stationary phases is given in chapter 3. 

---