Liquid stationary phase:
In liquid-liquid type, a liquid stationary phase is held on the support packing by physical adsorption while in bonded phase the stationary phase is bonded chemically to the support. One of the major drawbacks of the liquid-liquid system is the loss of stationary phase by dissolution in the mobile phase. This requires periodic recoating of the support particles. In addition, the solubility of the stationary phase prohibits the use of liquid-phase packing for gradient elution. However, with bonded-phase, these problems are mitigated to a huge extent. Within a majority of cases, a bonded- phase packings for partition chromatography are ready from rigid silica or silica based compositions. The Bonded phase packings are categorize as reversed phase while the bonded coating is non polar and as the general phase if the coating holds polar functional groups. Mostly in reversed phase the coating is a C8 chain (n-octyl) or a C18 chain (n-octyldecyl). For normal phase polar bonded phases that have a diol (-C3H6OCH2CHOHCH2OH), cyano (-C2H4CN), amino (-C3H6NH2) and dimethylamino (-C3H6N (CH3)2) functional groups are commercially available. We have seen that the nature of the stationary phase and the way it is held on the support are responsible for quite a few diversifications in liquid partition chromatography. If the solid support instead of holding the liquid acts as an active adsorbent, the related chromatography is known as liquid-solid adsorption chromatography. This statement is true for both column and 2D chromatography. Sometimes, it becomes difficult to distinguish whether it is the partition or the adsorption which is dominating in the separation.