Analysis of non-ionic surfactants used in tertiary oil recovery. Optimisation of stationary phase in normal phase partition chromatography

Summary Non-ionic surfactants, made from ethylene oxide units of various lengths condensed with long chain aliphatic alcohols, which are used extensively in enhanced crude oil recovery have been analysed in the past by both adsorption and normal phase partition chromatography. These methods work satisfactorily for narrow range polymers but are of no use for wide range higher molecular weight materials. We have investigated the performance of a new silica diol bonded phase and compared its chromatographic behaviour with amino and cyano bonded phases for the separation of non-ionic surfactants. After derivatisation with 3,5-dinitrobenzoyl chloride it was found that only the diol phase gave a good evaluation of the distribution versus the number of ethylene oxide units for three surfactants KL 6, KM 11 and KM 20 (the number represent the average number of ethylene oxide units in the molecule). Isocratic elution was used in the case of KL 6 and KM 11 and gradient elution for KM 20. In spite of the presence of over 40 peaks in the chromatogram of KM 20, analysis was accomplished in about 45 minutes. Identification of peaks was achieved by the coelution of a pure standard.