Analysis of extractable basic nitrogen compounds in Buliangou subbituminous coal by positive-ion ESI FT-ICR MS

Buliangou subbituminous coal (BSBC) was sequentially extracted with carbon disulfide, methanol, and acetone under ultrasonic irradiation to afford extracts 1-3 (E1-E3). All the extracts were analyzed with a positive-ion electrospray ionization (ESI) Fourier transform ion cyclotron resonance mass spectrometer (FT-ICR MS). In total, 11.11% of organic matter in BSBC was extracted with the three solvents. According to analysis with positive-ion ESI FT-ICR MS, the molecular masses of basic nitrogen compounds (BNCs) in E1-E3 range from 200 to 600 u and dominate from 250 to 450 u. The BNCs detected are mainly N1Ox (x = 0-2) and N2Oy (y = 0 and 1) with 4-25 of double bond equivalent (DBE) values and 12-38 of carbon numbers (CNs). The BNCs in E2 have lower DBE values (4-16) and CNs (14-28). According to DBE distributions, molecular core structures of most N1Ox classes should be aromatic rings, including benzene, pyridine, quinoline, and acridine rings. Moreover, core structures of most N1Ox moieties connected with an amino group or condensed with a pyrrole ring are characteristic structures for N2Oy classes in E1-E3. In addition, a small amount of amines (DBE < 4) were also identified in the extracts. Positive-ion ESI FT-ICR MS proved to be a powerful tool for identifying extractable BNCs in coals.