Simultaneous separation of nonionic surfactants and polyethylene glycols by reversed phase high performance liquid chromatography

The simultaneous separation of polyethylene glycol and its derivatives such as the lauryl alcohol and lauric acid ethoxylate oligomers was carried out by reversed phase high performance liquid chromatography. Branched fluorin ated silica gel columns combined with evaporative light scattering detectio n were used for the characterization of nonionic surfactants. Lauryl alcoho l ethoxylate oligomers were separated at 10 degrees C with an isocratic elu ent according to ethoxylate number and the retention time of the oligomers decreases with increasing ethoxylate number. The Van't Hoff plots of retent ion factor of lauryl alcohol ethoxylate gave a complex cure, which is anoma lous behavior for reversed phase high performance liquid chromatography. Th e anomalous Van't Hoff plots were explained by a partial conformational cha nge from polar to less polar conformers with increasing temperature. The mo st significant features for the analysis of the lauryl alcohol ethoxylate w ere the use of acetonitrile as mobile phase and operating temperature. The polyethylene glycol was separated according to ethoxylate number and the re tention time of oligomers increased with increasing ethoxylate number. The Van't Hoff plots of retention factor of polyethylene glycol had negative sl opes. It was presumed that the polar conformation of the ethylene oxide cha in decreased with increasing temperature. The lauryl alcohol ethoxylate and polyethylene glycol were separated simultaneously in gradient elution as a result of the conformational change of the ethylene oxide chain. As a prac tical example, lauric acid ethoxylate simultaneously separated into foe pol yethylene glycol, ethoxylate monolaurate and ethoxylate dilaurate in gradie nt elution.