The use of pain management drugs has been steadily increasing. As a result, labs are seeing an increase in patient samples that must be screened for a wide variety of drugs to prevent drug abuse and to ensure patient safety and adherence to their medication regiment. Therapeutic drug monitoring can be challenging due to the low cut-off levels, potential matrix interferences and isobaric drug compounds. To address these challenges, many drug testing facilities are turning to liquid chromatography coupled with mass spectrometry (LC-MS/MS) for its increased speed, sensitivity, and specificity. In this example, a method was developed for a multi-class drug and metabolite screen containing 231 compounds.

There are many challenges one must consider when developing a large screening assay. Experiments performed included mobile phase considerations, sample diluent, isomer resolution, drug interferences, and instrumentation capabilities. Analytes were diluted in water and injected into a Shimadzu Nexera UHPLC equipped with an AB SCIEX API 4500™ MS/MS. Detection was performed using electrospray ionization in positive and negative ion modes using scheduled multiple reaction monitoring (MRM).

During mobile phase investigations, it was found that methanol provided the best retention of early eluting analytes, such as morphine, oxymorphone, nicotine and norcotinine. Sample diluent was optimized to improve the peak shape of the early eluting compounds. Scan rates and retention time windows were optimized to ensure enough data points per peak were collected.

231 compounds with a final optimized separation gradient run time of 10minutes, with a total cycle time of 12minutes.