Comprehensive two-dimensional separation for the analysis of alkylphenol ethoxylates employing hydrophilic interaction chromatography coupled with ion mobility-mass spectrometry

Abstract

A comprehensive two-dimensional system coupling hydrophilic interaction chromatography (HILIC) and ion mobility-mass spectrometry (IM-MS) has been developed for the separation and analysis of alkylphenol ethoxylates (APEOs). The first-dimensional HILIC was performed on porous silica stationary phase using acetonitrile–water gradient elution, which was readily compatible with electrospray ionization (ESI), and enabled good chromatographic separation of APEO oligomers on account of their differences in ethoxy chain length. Maintaining the fidelity of pre-ionization resolution in the first dimension, the second-dimensional IM-MS employed a hybrid quadrupole ion mobility time-of-flight mass spectrometer and added an orthogonal post-ionization separation for APEOs based on their size, shape and electric charge during a very short period of 13.0ms. By virtue of the combination of HILIC and IM-MS, comprehensive resolution according to both hydrophobicity difference and mobility disparity has been achieved for APEO ethoxy homologues. The orthogonality of the developed two-dimensional system was evaluated with the correlation coefficient and peak spreading angle of 0.2191 and 77.34° for octylphenol ethoxylates (OPEOs), and 0.1490 and 81.43° for nonylphenol ethoxylates (NPEOs). A significant enhancement in peak capacity was achieved for the comprehensive two-dimensional plane with the actual peak capacity calculated to be approximately 7 and 122 times higher than that of the two dimensions used alone, respectively. The attractive potential for removing the effects of isobaric interference of APEOs by the rapid and solvent-free ion mobility approach was also highlighted.