Quantification of Polyethylene glycol (PEG) as impurity in Surfactants (Ethoxylates) using third-order model performed by HPLC accoupled to Evaporative Light Scattering Detector (HPLC-ELSD)

Polyethylene glycol is formed by homopolymerization of ethylene oxide competition to the desired reaction of the addition of ethylene oxide to the hydrophobic initiator. Formation of PEG is initiated by traces of water in the reaction medium. PEG does not have surfactant properties and its presence is therefore undesirable. The homolog distribution of PEG is usually similar to, but broader than, the homolog distribution of the surfactant. There are several methods for the determination of PEG in fatty alcohol and alkyl-phenol ethoxylates, as gravimetric method; however, such a procedure; gives low recoveries with PEG of low molecular weight. Gravimetric procedure is therefore not suitable for the analysis of products with a degree of ethoxylation of less than 6 units, while the HPLC and TLC procedures are suitable over both low and high molecular weight ranges. The separation in the present method is carried out using a C18 column, an Acetonitrile/water gradient, and ELSD detection. ELS detector (Evaporative Light Scattering Detector) is one of the most universal detectors available for HPLC. ELSD measures many semi- and non-volatile analytes and does not require an analyte to possess a chromophore or ionizable group. ELSD are aerosol-based detectors that work by converting the eluents of target components (carried by an inert carrier gas such as nitrogen) to a fine spray via a nebulizer, then the mobile phase is evaporated through a Drift tube by heating, Light is then focused on the remaining target substance and scattered light is detected. The presented method has been demonstrated to be lineal, accurate, and precise in determining PEG in Ethoxylates among the range 0.01% w/w to 0.5% w/w. The determination is quantitative and is made by preparing a third-order calibration curve with PEG standard.