Adsorption of methanol from the liquid mobile phase on the column packing surface

The adsorption isotherms of methanol in water solutions which were used as mobile phase in RP HPLC on adsorbents modified with dimethyloctadecylchloro silane were measured. On the basis of these isotherms the chemical composit ion of the stationary phase as a function of the mobile phase concentration was determined. The influence of both those phases on retention factors k of alkyl derivatives of benzene was discussed. It was stated that k' of ben zene and its derivatives decreases with the various rate together with the increase of the methanol concentration in both phases. Quotient of volume c oefficient corresponding to a unit of adsorbed methanol (logk/n(Me)(s)) dec reases linearly.