[Determination of hydrophobic parameters (log PHPLC) for methacrylates, initiators and miscellaneous compounds used in dentistry by high-performance liquid chromatography (HPLC) (author's transl)].

The use of partition coefficients Poct obtained from an n-octanol-water partitioning system has become a standard method for modelling biological membranes and thereby quantifying the hydrophobicity of a given compound as log Poct = log Coct--log Cwater. However, there is no convenient method available to determine the log Poct value accurately. The conventional flask-shaking method is a laborious and time consuming procedure, often complicated by instability in aqueous media, impurities and the tendency for the compound to dissociate. There have been recently attempts using HPLC to determine the hydrophobicity of organic compound. The retention behaviour of about fifty organic compounds in HPLC systems have been examined. Using methanol-water as the mobile phase, a linear relationship between the volume fraction of organic modifier and the logarithm of the capacity factor (log K') over limited range was obtained for standards. However, unfortunately, the correlation between log Kw obtained from the extrapolated K' values with pure water as eluent and log Poct values was not good (r = 0.83). Using this octadecylsilyl column with the mobile phase (methanol: water = 70:30), standards fall on the three straight lines with good correlations (r = 0.99) between the log Poct and log K' values.: one for benzenes and aliphatic compounds, the second for phenols, anilines and hydrogenacceptor benzene derivatives and the third for benzoic acids, respectively. The PHPLC values of methacrylates, initiators and miscellaneous compounds which are widely in dentistry were determined using these three regression lines.