Two types of isotope-labelled reference compounds are typically used for the passive sampling of polycyclic aromatic hydrocarbons. One type is added before the exposure of the sampler and is called a performance reference compound (PRC). The other is the laboratory internal standard, which is spiked into the sample after extraction (dialysis) from the membrane and is used for quantification. Generally, PRCs are deuterium-labelled while internal standards are ¹³C-labelled. Interference originating from the internal standards occurs when the molecular ions of the PRCs gradually lose deuterium in the ion source to generate fragments that overlap with the molecular ions of the ¹³C-labelled internal standards. This can cause significant systematic errors in quantification. Gas chromatography-high resolution time-of-flight mass spectrometry (GC-HRTOF-MS) was used to investigate the degree of interference at varying virtual resolutions of the MS instrument, and it was shown that many of the spectral interferences can be avoided by using high MS resolutions (35 000 or better).