We have applied electrospray ionization (ESI) Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) to analyze the pyridine soluble fraction of a distillation resid and a further processed liquid product in a coal liquefaction process. The inherent high resolving power (m/Delta m(50%) > 300,000, in which Am-50% is full mass spectral peak width at half-maximum peak height) and mass accuracy (< 1 ppm) of FT-ICR MS makes it possible to resolve and identify polar heteroatomic species. The resid contains more heteroatomic compounds and a higher molecular weight distribution whereas the liquid sample is lower in average mass and more saturated. The data confirms that the liquefaction process produces lower mass, hydrogenated liquid product whereas the resid (highly aromatic and of high heteroatom content) must be recycled to reduce its heteroatom content and increase its degree of saturation. (c) 2005 Elsevier Ltd. All rights reserved.