Simultaneous Quantitation of 78 Drugs and Metabolites in Urine with a Dilute-And-Shoot LC-MS-MS Assay

A novel LC-MS-MS assay that simultaneously detects and quantitates 78 drugs and metabolites was developed and validated for chronic pain management. Urine specimen was diluted and mixed with internal standards (ISs) before injected into LC-MS-MS. Seventy-two analytes were detected with positive electrospray ionization mode and the remaining six analytes with negative mode. Two separate gradient elution chromatographic programs were established with the same mobile phases on the same bi-phenyl HPLC column. The assay was linear for all analytes with linear regression coefficient ranging 0.994-1.000. The intra-assay precision was between 1.7 and 8.8% and inter-assay precision between 1.9 and 12.2%, with bias <20% for all but six analytes. All analytes in urine specimens were stable for 7 days at 4 degrees C, and no significant matrix effect or carryover was observed. A suboptimal recovery rate (60.0-156.8%) was observed for six analytes, potentially due to the lack of available deuterated ISs, requiring comparison to a chemically different IS. Method comparison using patient and proficiency testing samples demonstrated that this assay was sensitive and accurate. The assay improves on currently existing assays by including glucuronide conjugates, allowing direct detection of metabolites that might otherwise be missed by existing methods.