Identification of Novel Opioid Interferences using High-Resolution Mass Spectrometry

Novel opioid interferences were observed during the development of a high-resolution liquid chromatography-mass spectrometry urine drug testing method for 47 analytes from multiple drug classes. The interferences affected both analytes and internal standards and were only observed when the method was challenged with patient samples. Some interferences were attributable to isomeric opioid metabolites not previously reported while others were due to interference from in-source dissociations or C-13 isotopic contributions from known opioid metabolites not typically monitored as analytes. Based on patient drug profiles, known and inferred metabolism, accurate mass, retention time and MS/MS spectrum, the putative identity of each interference was assigned and later confirmed, when possible, using an authentic standard. Opioids are some of the most frequently monitored analytes in urine drug testing laboratories. Because of the potential for co-purification, co-chromatography and spectral similarity, it is anticipated that the reported opioid metabolite interferences could be present with other method conditions and instrument platforms. The objectives of this work are to raise awareness of these interferences and emphasize the importance of evaluating patient samples for potential interferences during method development.