Enriching And Characterizing Organic Soluble Fractions Of Four Chinese Lignites Based On Solid-Phase Microextraction

Due to the low calorific value,high contents of moisture,and high ash yield,etc,low-rank coals like lignites are unsuitable to be used as fuel.So it is essential to understand the structure of low-rank coals deeply at molecular level for their high value-added utilization.Solid-phase microextraction(SPME)is applied to analyze thermally extractable solutions(TESs)of lignites,different components in TESs can be enriched selectively by SPME coatings with different physicochemical properties so that more complete structural information of lignites can be obtained.In this work,Dongming,Zhaotong,Xiaolongtan and Baiyinhua lignites were selected as the coal samples.Paralleled thermal dissolution at the temperature of 300~oC using methanol,isopropanol and benzene was conducted to afford TESs of lignites.Polydimethylsiloxane(PDMS)and polypyrrole(PPY)were selected as SPME coatings and their extraction conditions were optimized,then enrichment characteristic of these two coatings toward components in TESs was analyzed via GC/MS and Orbitrap MS.There was strong competition between different components in TESs during the enrichment of SPME coatings,which means that one SPME coating can only enrich the components with specific structure or physicochemical properties instead of all the components in TESs.The optimum extraction conditions of PDMS is extraction time of 60 min and extraction temperature of 25 ~oC.PDMS coating is able to enrich n-alkanes and aromatic compounds with long or many alkyl chains selectively so it is suitable to combine PDMS coating and GC/MS to analyze biomarkers in TESs of lignites.The optimum extraction conditions of PPY particles is extraction time of 30 min and extraction temperature of 25 ~oC,PPY particles are able to enrich Oo species in TESs,in the meantime,their dislodgement effect toward NOo species weakens the negative influence caused by the ionic reaction of NOo species during the in-source collision-activated dissociation(ISCAD).After enriched by PPY particles,there is more compounds with heteroatoms existing in alkyl chains in the components in TESs,in addition,there are more heterocyclic units in Dongming lignite compared with Zhaotong lignite.Heteroatom-containing components can be enriched and analyzed effectively by combining PPY coating and DART-Orbitrap MS,and the total analysis time of single sample is less than 2 min.The results obtained in this work provided new insights in analyzing TESs of lignites.