The autothermal reforming of middle distillates is a favored reforming technique for fuel cell-based auxiliary power units (APUs) in the transport sector. The efforts made in recent years to produce a high quality reformate have been reflected in a variety of improvements to the reactors and mode of operation of the fuel processing systems. By these means, the concentrations of contaminants, especially traces of hydrocarbons in the gas phase, frequently drops below the previous detection limit. In this paper, a new GC/MS method is developed to reduce the detection limit of the analytics into the sub-ppm range. This work is intended to serve as a valuable step to showing which traces of hydrocarbons can still be qualitatively and quantitatively expected in a high quality reformate. This contribution may help determine the multitude of hydrocarbonous substances that can have a detrimental long-term effect on catalysts and adsorbents in a fuel cell-based APU system operated with middle distillates. (C) 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.