Water-Assisted Dispersive Solid Phase Extraction For The Identification Of Organic Nitrogen Compounds In Gasoline By Liquid Chromatography-High Resolution Mass Spectrometry

Nitrogen compounds(NCs)in fuel oil will bring economic losses to chemical production.Various oxides will be generated after combustion and enter the atmosphere,resulting in environmental pollution,photochemical smog,acid rain,carcinogenic effect on human body,causing various skin and respiratory diseases,so NCs in fuel oil needs attention.In order to better understand the types and contents of these NCs,efficient methods are needed to analyze and identify them,and provide theoretical basis for subsequent standard specifications and removal efficiency evaluation.In the analysis of NCs in fuel oil,liquid chromatography-high resolution mass spectrometry(LC-HRMS)is more advantageous for the identification of new substances.However,because the fuel matrix is not compatible with LC,how to efficiently and quickly extract low concentration of nitrogen compounds matter from fuel and accurately analyze and identify it has always been the focus of research.In this study,an analytical method based on water-assisted dispersed solid phase extraction(DSPE)combined with LC-HRMS was established.In this method,a mixed mode cation exchange filler(MCX)was used as the adsorbent of DSPE.A small amount of water was dispersed into the gasoline sample during extraction to assist the ionization of NCs.The enhancement of ion exchange between adsorbent and NCs can significantly improve the extraction efficiency.Through further optimization of p H,water dosage,loading time,eluting solvent,elution solvent,loading volume and other conditions,the efficient enrichment of trace NCs in gasoline was realized.For the 14 NCs,they had high recovery(70.6%-102.5%)and good reproducibility(intraday RSDs≤3.6%and interday RSDs≤5.8%).The limits of detection(LOD)and quantification(LOQ)were 0.06-3.16μg/L and 0.2-10μg/L,respectively,when detected by liquid chromatography-UV detector(LC-UV),and the range of quantification remained linear in the range of 0.05-500 mg/L(R~2>0.992).Aniline,M-toluidine and N-methylaniline were detected by comparing the retention time of the standard sample.The concentrations of Aniline,M-toluidine and N-methylaniline were 2.21,7.09 and0.71 mg/L.When the prepared samples were detected by LC-HRMS,the LOD could be as low as0.1-5 ng/L,which can further meet the requirements for the analysis and identification of low concentration NCs in fuel.The second analysis of 92#gasoline showed that there were seven NCs including Aniline,M-toluidine,N-methylaniline,Pyridine,Quinoline,Indoline,N,N-diethylaniline in the sample.A large number of unknown NCs were also found,and the existence of isomers was also very common.During the identification,the ion m/z=122.09643 and 136.11208 with relatively high abundance were selected as the identification targets.Due to the existence of isomers,they must be separated on the chromatography to identify each isomer,the gradient optimization of liquid chromatography was carried out on the ion,and its secondary spectrum was collected.By analyzing the secondary spectrum of each peak,the structures of 16 isomers were deduced,7 of which m/z=122.09643 and 9 of which m/z=136.11208.Among them,seven newly discovered NCs were reported for the first time in this study.In this study,trace NCs in gasoline was enriched and accurately analyzed and identified.The total time of sample pretreatment was less than 25min,which has the advantage of high efficiency and fast.It provides method reference and data support for the analysis of NCs from fuel oil.It also has the potential to be applied to the analysis of NCs in other fuels.