Characterization and analysis of non-ionic surfactants by supercritical fluid chromatography combined with ion mobility spectrometry-mass spectrometry

Comprehensive separation and analysis of non-ionic surfactants have been conducted by coupling supercritical fluid chromatography (SFC) with ion mobility spectrometry-mass spectrometry (IMS-MS). Representative non-ionic surfactants were investigated, including alkylphenol ethoxylates (APEOs), e.g., octylphenol ethoxylates (OPEOs) and fatty alcohol ethoxylates (FAEs), e.g., lauryl alcohol ethoxylates (LAEs). A sub-2-μm high-density diol column was used for chromatographic separation by the first-dimensional SFC due to the differences in ethoxy chain prior to electrospray ionization (ESI). Maintaining the fidelity of pre-ionization separation in the first dimension, the introduction of IMS provided additional post-ionization resolution by broadly fractionating the oligometric ethoxymers based on their size and electric charge within 13.78 ms. Distinguishable series of singly and multiply charged non-ionic species could be clearly observed. The millisecond timescale ion mobility separation perfectly fits the elution time of a chromatographic peak, while effectively feeding components into the fast-scanning time-of-flight (TOF) mass analyzer for characterization and analysis. The orthogonality of the developed separation and analysis system was evaluated, revealing a correlation coefficient and peak spreading angle of 0.2729 and 74.16° for the studied OPEOs and 0.1962 and 78.69° for LAEs. Significant enhancement in peak capacity was achieved for the developed SFC-IMS-MS system with the actual peak capacity measured to be approximately 41 and 160 times higher than that of the dimensions of SFC and IMS, respectively, when used alone.