The effect of co-occurring polychlorinated biphenyls on quantitation of toxaphene in fish tissue samples by gas chromatography negative ion mass spectrometry

► Oxygen adducts of a co-occurring PCB contributed up to 88% of the NCI-MS response. ► A three-step procedure was developed to remove PCB-oxygen adduct interferences. ► Total toxaphene was 12-75% of the concentration without correction for PCBs. ► Quantitation of 8 toxaphene congeners was not impacted by co-occurring PCBs.