Analytica Chimica Acta 477 (2003) 293–303 Analysis of polyethoxylated surfactants in microemulsion-oil–water systems III. Fractionation and partitioning of polyethoxylated alcohol surfactants N. Márquez a,∗ , B. Bravo a , F. Ysambertt a , G. Chávez a , N. Subero a , J.L. Salager b a Laboratorio de Petroqu´ ımica y Surfactantes, Dpto. de Qu´ ımica, Facultad de Ciencias, La Universidad del Zulia, Apdo. 526 Maracaibo, Zulia, Venezuela b Laboratorio FIRP, Ingenier´ ıa Qu´ ımica, Universidad de los Andes, Mérida, Venezuela Received 10 April 2002; received in revised form 25 September 2002; accepted 28 October 2002 Abstract Oligomer distribution of polyethoxylated alcohol and polyethoxylated nonylphenol surfactants is studied by normal and reverse-phase high performance liquid chromatography (HPLC). A RP8 column is able to efficiently separate these surfactants according to their alkyl chain (lipophilic) group, while silica and amino columns separate them according to their polyether chain length (hydrophilic group). Polyethoxylated alcohol and polyethoxylated nonylphenol oligomers selectively partition between the microemulsion-oil–water phases of a Winsor III system. Partitioning of these oligomers was analyzed by HPLC with RI detection. The logarithm of the partition coefficient between the water and oil linearly increases with the number of ethylene oxide groups per molecule of oligomer. For a same ethoxylation degree, the partition coefficient of a polyethoxylated tridecanol is found to be higher than the one of the corresponding nonylphenol specie. On the other hand, a polyethoxylated nonylphenol exhibits a higher solubilization than the matching polyethoxylated alcohol. © 2002 Elsevier Science B.V. All rights reserved. Keywords: Partitioning; Surfactants; Ethoxylated alkylphenol and ethoxylated alcohol; HPLC separation 1. Introduction Polyethoxylated nonylphenol surfactants (PNS) have been used for a long time for different applica- tions. A few years ago, Venezuela petroleum industry used this kind of surfactant to produce over 100.000 Bl per day of bitumen in water emulsion commercialized as a fuel substitute for thermoelectrical plants. Recent ∗ Corresponding author. Tel.: +58-261-783-4055; fax: +58-261-759-8125. E-mail address: nmarquez@zul.reacciun.ve (N. M´ arquez). regulations in Europe banned the use of alkylphenol surfactants for this purpose, and they had to be re- placed by polyethoxylated alcohol surfactants (PAS) with an average of 13 carbon atoms in their alkyl chain. Thus, an analytical method to study these surfac- tants in surfactant–oil–water systems had to be deve- loped. Some previous research has been dedicated to the determination of the EON distribution in PNS by various analytical procedures, mainly of the chromato- graphic type like gas chromatography [1,2], normal- phase high performance liquid chromatography 0003-2670/02/$ – see front matter © 2002 Elsevier Science B.V. All rights reserved. PII:S0003-2670(02)01407-1