Comparative Analysis of ELISA Immunoassay and LC-QTOF for Opiate Screening

A comparative analysis of enzyme-linked immunosorbent assay (ELISA) and quadrupole time-of-flight mass spectrometry (LC-QTOF) for the detection of opioids in blood samples is presented. The Orange County Crime Lab (OCCL) was concerned that the opioid drug class was not accurately detected at low concentrations due to the use of LC-QTOF as a non-targeted screening method for multiple classes of drugs. In order to investigate this issue, 968 ante-mortem and postmortem blood samples were analyzed by ELISA for the presence of the following opioids: morphine, morphine-glucuronide, codeine, codeine-glucuronide, hydrocodone, hydromorphone, hydromorphone-glucuronide, oxycodone, oxymorphone and oxymorphone-glucuronide. All samples had been previously analyzed by LC-QTOF. Overall, 84 samples tested positive for opioids. Discrepant samples between ELISA and LC-QTOF were analyzed by a liquid chromatography tandem mass spectrometry confirmation method in order to determine the true composition of the sample. Upon review of the discrepant samples, no forensically relevant concentration of opioids was missed by LC-QTOF. Thus, the ability of the OCCL’s LC-QTOF screening method was verified to detect opioids at low concentrations.