Determination of fatty alcohol ethoxylates by derivatization with phthalic anhydride followed by liquid chromatography with UV–vis detection

Abstract

The esterification of fatty alcohol ethoxylates (FAEs) with phthalic anhydride in 1,4-dioxane was studied. At 110 °C and in the presence of urea, which increased the reaction rate, esterification was completed in 60 min. The reaction yield did not decrease when the sample contained up to 50% water. For the non-ethoxylated alcohols, the UV–vis response factors of the derivatives were not significantly different from each other ( f = 1 for C12E0 as reference). The response factors decreased when the number of ethylene oxide units, m, increased, reaching constant values of ca. 0.40 and 0.65 for the n = 8 and 18 series, respectively, when m ≥ 3. Using a C8 column and gradient elution with acetonitrile/water plus 0.1% acetic acid, FAEs in industrial mixtures and cleaning products were characterized. At column temperatures of 25 and 35 °C, homologous series with even values of n from 8 up to 20, were resolved up to m = 14 and 18, respectively, and at 25 °C, series with consecutive even and odd values of n were resolved up to m = 7. Within the series, superior resolution of the ethoxymers with large values of m was achieved; however, the elution order was reversed for the m = 1 and 0 ethoxymers, which produced overlapping of a few peaks within the series. A simple procedure for the accurate prediction of the concentrations of all the ethoxymers in industrial samples was described. After preconcentration with C18 solid-phase extraction cartridges, FAEs were also characterized and quantified in environmental samples (river and sea water). The LODs were ca. 2 μM ( S/ N = 3) in the injected solutions.