Retention behavior of ethoxylated nonionic surfactants with different hydrophobic moieties by RP-HPLC

The retention behavior of polydisperse ethoxylated fatty alcohols with the same ethoxylation degree but various alkyl chain lengths (CnEO10, n = 12, 1 4, 16 and 18) has been investigated by reversed-phase high-performance liqu id chromatography (RP-HPLC) as a function of methanol content of the mobile phase. The linear correlation between the logarithm of capacity factor, lo w k', and the eluent composition was used to determine the standard hydroph obicity parameter, k(w). The change of k(w) with the alkyl chain length of surfactants resulted in a value of -2.81 kJ/mol for the free energy of tran sferring one methylene group from water to nonpolar stationary phase. This value is in agreement with the reported value of about -2.85 kJ/mol obtaine d from micellization data for the same surfactants.