Determination of Organic Nitrogen Compounds in Gasoline by Water-Assisted Dispersive Solid-Phase Extraction (DSPE) and High-Performance Liquid Chromatography-High-Resolution Mass Spectrometry (HPLC-HRMS)

For the identification of trace-level organic nitrogen compounds (NCs) in gasoline, a method consisting of water-assisted dispersive solid-phase extraction (DSPE) and high-performance liquid chromatography-high resolution mass spectrometry was developed in which mixed-mode cation exchange was used as the adsorbent. To increase the DSPE efficiency, water was dispersed into the gasoline to increase the pronation of NCs and enhance the ionic interaction with the adsorbent. After systematic optimization of DSPE conditions, including the adsorbent mass, sample volume, water to gasoline ratio, sample loading time, washing and elution solvents, sensitive determination of NCs (detection limits from 0.1 to 5 ng/L for the 14 analytes) was achieved by this method with a 100-fold enrichment. A number of unknown NC isomers were observed from the extracted ion chromatograms based on the accurate determination of mass-to-charge ratio (m/z), from which two sets of isomers at theoretical m/z of 122.09643 and 136.11208 were selected for identification. By careful elucidation of the product ion spectra of the selected ions, 16 NCs were putatively identified, in which six non-aniline homologs were reported for the first time.