Analysis of aliphatic alcohol ethoxylates in terms of alkyl and ethylene oxide chain lengths by reversed-phase liquid chromatography with evaporative light scattering detection

Aliphatic alcohol ethoxylates are nonionic surfactants which are incorporated in many industrial formulations as complex mixtures of alkyl homologs and ethylene oxide oligomers. Determination of both the homolog and oligomer distributions is required for product control. The proposed method consisted of three reversed-phase liquid chromatographic separation steps carried out on the same C18-bonded silica column. The first step was a preparative one: the sample mixture was fractionated according to the alkyl chain length without discrimination between ethylene oxide oligomers by using methanol–water eluent. The even homologs (EH) were collected together in a single fraction, the odd homologs (OH) in another. In the second and third steps, respectively, EH and OH fractions were separated according to the alkyl chain length and the number of ethylene oxide units simultaneously by changing the mobile phase composition to acetonitrile–water and by using evaporative light scattering detection.