Commercial normal-phase:
In commercial normal-phase bonded packings, the R in the siloxane structure is a polar functional group such as cyano (-C2H4CN), diol (-C3H6OCH2CHOHCH2OH), amino (-C3H6NH2), and dimethylamino (C3H6N (CH3)2). The polarities of these packing materials vary over a considerable range with the cyano type being the last polar and the amino types the most. Diol packings are intermediate in polarity. With normal phase packings, elution is carried with relatively non-polar solvents such as ethyl ether, chloroform and n-hexane.
Figure: Relationship between the polarity of the sample with that of the packing material and the mobile phase in reverse phase HPLC