Packing Material or Stationary Phase:

The packing used in modern HPLC consists of small, rigid particles having a narrow particle size distribution. The most general packing material used for LC is prepared from silica (acidic) and alumina (basic) particles which are synthesized by agglomerating submicron size particles under conditions that lead to larger particle diameter. These are frequent coated along with thin organic films that are physically or chemically bonded to a surface. To nearly all HPLC applications, chemically modified or unmodified micro particulate silicas of 3, 5 or 10 µm diameter are preferred. This form of LLC, in that both monomeric and polymeric phases have been bonded to a huge range of support materials, is known bonded phase chromatography (BPC). Characteristics of typical packing materials used in HPLC are listed within Table a particles used in HPLC, that are totally porous (macroporous) or superficially porous (pellicular) support, may be spherical or irregular in shape but it is essential that the size range is as narrow as possible to

Table 8.2:  Characteristics of Some Commercial HPLC Column Packing Materials

ensure high column efficiency and permeability. These adsorbent packings retain solute molecules almost exclusively on the internal surface of the pores, thus, separating these from others. Several types of bonded phases used in HPLC are schematically shown in Figure.

Figure: Various shapes of stationary phase packings used in HPLC: (a) Bonded (spherical) phase; (b) Irregular large porous phase; (c) Pellicular particle beads and (d) Porous microparticle