Application of Accurate Mass Measurement to Urine Drug Screening

Poor availability of reference standards for designer drugs, metabolites, and new substances prevents toxicology laboratories from rapidly responding to the changing analytical challenges of drug abuse. A novel screening approach comprising determination of accurate masses of sample components and comparison of these with databases of theoretical monoisotopic masses is described. Using liquid chromatography-time-of-flight mass spectrometry (LC-TOFMS), a routine mass search window of 20-30 ppm was applied to urine samples. The ultimate reference technique, liquid chromatography-Fourier transform mass spectrometry (LC-FTMS), was capable of confirming the findings within a 3 ppm mass accuracy. Using a target database of 7640 compounds, the number of potential elemental formulas ranged from one to three with LC-TOFMS, and it was always one with LC-FTMS. In contrast to ordinary techniques requiring primary reference standards, the formula-based databases can be updated instantly with fresh numeric data from scientific literature and authority sources.