High resolution NMR for the direct characterisation of complex polyoxyethylated alcohols (CiEj) mixtures

High resolution 1H and 13C NMR were used to characterise complex mixtures of industrial polyoxyethylated surfactants of the CiEj series. A progressive methodology was applied to analyse mixtures of monodisperse surfactants of increasing complexity, with regard to both the alkyl chain (i = 8–16) and the polyoxyethylene moiety (j = 1–8). The techniques were then successfully applied for the characterisation of narrow- and broad-range commercial surfactants and to analyse the widely used Brij 30. It appears that direct high resolution NMR analysis of ethoxylated alcohol mixtures offers simultaneously a good description of the alkyl chain composition as regards to the length distribution and branching, together with an accurate overview of the oxyethylene oligomeric distribution for ethoxylates containing up to eight units. Finally NMR allows to check free alcohol and free polyethylene oxide that may exist in commercial surfactants.