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

Aliphatic alcohol ethoxylates are nonionic surfactants which are incorporat ed in many industrial formulations as complex mixtures of alkyl homologs an d ethylene oxide oligomers. Determination of both the homolog and oligomer distributions is required for product control. The proposed method consiste d of three reversed-phase liquid chromatographic separation steps carried o ut on the same C-18-bonded silica column. The first step was a preparative one: the sample mixture was fractionated according to the alkyl chain lengt h without discrimination between ethylene oxide oligomers by using methanol -water eluent. The even homologs (EH) were collected together in a single f raction, the odd homologs (OH) in another. In the second and third steps, r espectively, EH and OH fractions were separated according to the alkyl chai n 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. (C) 2000 Elsevier Science B.V. All rights rese rved.