Hydrophile-lipophile properties of ethoxylated nonionic surfactants as revealed by reversed-phase high-performance liquid chromatography (RP-HPLC)

The chromatographic behavior of nonionic surfactants was studied by RP-HPLC using an octylsilica column (RP-8, 10 m, 4.6 x 200 mm). The eluents were t he methanol-water mixtures and the detection was done at 280 nm. The surfac tants taken into consideration were polydisperse ethoxylated fatty alcohols and nonylphenols. The former were compared with their homogeneously ethoxy lated counterparts. The relationship between the capacity factor and the el uent composition was used to obtain the hydrophobicity parameters k(w) (the capacity factor with pure water as the eluent) and phi(0) (the organic mod ifier content of the mobile phase required for fog k' = 0). A linear relati onship was observed between them and the HLB values of surfactants. The ano malous comportment of k(w) for ethoxylated nonylphenols was explained by co nformational changes of the PEO chain. The RP-HPLC proved to be a reliable and useful tool to investigate the hydrophilic-lipophilic properties of eth oxylated surfactants.