Ruthenium ion-catalyzed oxidation of the extraction residue from Shenmu coal char powder (ERSCCP) was conducted. The resulting soluble portions (SPs) were analyzed with a gas chromatograph/mass spectrometer (GC/MS) and direct analysis in real time/time-of-flight mass spectrometer (DART/TOF-MS) to obtain carboxylic acids and to understand the structural feature of ERSCCP. The results show that benzenepolycarboxylic acids with 3-6 carboxy groups are predominant in the SPs, suggesting that ERSCCP is rich in highly condensed aromatic moieties. In addition, small amounts of long-chain alkanoic acids were detected with GC/MS. According to analysis with positive-ion DART/TOF-MS, [M - OCH3](+) and [M + NU4](+) are dominant ions generated from polymethylbenzenepolycarboxylates (PMBPCs) in the methyl esterified SPs. A series of dimers and trimers of PMBPCs were also identified with positive-ion DART/TOF-MS. (C) 2016 Elsevier B.V. All rights reserved.