CHROMATOGRAPHIC QUANTIFICATION OF HYDROPHOBICITY USING MICELLAR MOBILE PHASES

In micellar liquid chromatography (MLC), the hydrophobicity of a compo und is the predominant effect on its retention and interaction with mi celles; however, some contradictory results have been obtained concern ing whether k or log k best correlates with the logarithm of partition coefficients (log P) in the biphasic solvent system octanol-water. An empirical model which describes the relationship between retention in MLC and log P is presented. The retention data for series of neutral compounds eluted with different pure and mixed mobile phases and alkyl -bonded stationary phases were used to test the model. The results ind icate that non-linear relationships between k or log k and log P are t o be expected and only in particular circumstances can linear relation ships be obtained. In contrast, in all the series studied, excellent c orrelations between the logarithm of the retention factor at zero mice llar concentration, k(m), and log P, were found (r(2) in the range 0.9 65-0.987 and F in the range 277-608). Log k(m) is proposed as the best chromatographic index for the quantification of the hydrophobicity of solutes using micellar mobile phases.