91Ó°ÊÓ

At all pH values, Acetophenone is neutral and its retention remains unaffected by pH.

In case of Salicylic acid, a neutral molecule HA can be expected. The expected neutral molecule HA might have certain affinity for the${\mathrm{C}}_8$non-polar stationary phase and the ion${\mathrm{A}}^{-}$might have little affinity for${\mathrm{C}}_8$Salicylic acid is mostly HA below pH 2.97 and above pH is likely shows${\mathrm{A}}^{-}$At pH =3 there is 1: 1 ratio mixture of HA and${\mathrm{A}}^{-}$that is soberly retained on the non-polar column. At pH5 and 7 , maximum of molecules (more than 99% ) shows${\mathrm{A}}^{-}$hence the retention is weak(retention factor is small).

Nicotine in its ionic form is subjected to have less affinity for non-polar stationary phase and the neutral molecule shows affinity to certain extent.

Considering Nicotine as B, the form B is most preferable at above$\mathrm{pH}={\mathrm{pK}}_2=7.85{\mathrm{BH}}^{+}$is most likely between pH3.15 and7.85

${{\mathrm{BH}}_2}^{2+}$is most preferable at below 3.15pH

B doesn't become appreciable till pH is approximately equal to 7 , hence the retention factor is less below pH 7 and raise at pH7.