Supercritical fluid extraction and chromatography of non-ionic surfactants combined with FTIR, APCI-MS and FID detection

Abstract

This paper describes a supercritical fluid extraction (SFE) method for the analysis of non-ionic surfactants in a washing powder. By varying the SFE conditions it was possible to fractionate the extracts according to their polarity. The subsequent analysis and identification of the non-ionic surfactants by supercritical fluid chromatography (SFC) combined with Fourier transform infrared or mass spectrometry detection (SFC-FTIR, SFC-MS) did not require any additional sample preparation. Most non-ionic surfactants were extracted by SFE without using a modifier to enhance the polarity of the supercritical carbon dioxide (scCO₂) (fraction (a)). Two further substances could then be extracted using scCO₂ with 5% methanol as a modifier (fraction (b)). The SFC-FTIR chromatogram suggested that fraction (a) consisted of six groups of surfactants of which four were identified as ethoxylates from their SFC-FTIR spectra. Using SFC-MS, an identification of each alkyl polyglycol ether constituent was possible and the presence of phenol polyglycol ethers could be excluded. The SFC-FTIR spectra of two additional peaks in fraction (a) suggest that one could be due to a tert-butyl ester, the other one to an α/β-unsaturated ester. These suggestions could not be confirmed by the SFC-MS analysis since the corresponding peaks were too weak to obtain a suitable fragmentation pattern. The two components extracted in fraction (b) (also apparent in fraction (a)) were identified as fatty acids, which could be due to breakdown products or impurities of anionic surfactants.