Optimization and validation of a method for rapid quantitation of fentanyl in seized‐drug samples using direct analysis in real time mass spectrometry (DART‐MS)

The rise of illicitly manufactured fentanyl and fentanyl-related substances has overwhelmed seized-drug laboratories and resulted in an explosive surge of analysis requests, increasing backlogs and turn-around times. Direct analysis in real time (DART) ionization in combination with mass spectrometry has proven valuable as an identification tool for forensic laboratories by providing fast and reliable results. However, its application for quantitative analyses has been limited. In this work, the standardized DART-mass spectrometry (MS) qualitative method used throughout Drug Enforcement Administration laboratories was optimized and validated for rapid quantitation of fentanyl-containing samples. Sample solutions were prepared in methanol and ionized using a 3-s pulse of metastable helium atoms, while protonated molecular ions for fentanyl and fentanyl-d5 were monitored over a 12-s MS acquisition window using selected-ion monitoring. Measured peak area ratios resulted in great linear behavior (r > 0.999) over a fentanyl concentration range of 2-250 μg/mL and a calculated LOQ of 3.8 μg/mL. Validation of the method demonstrated excellent within-batch and between-day precision (relative standard deviations <6%) and high accuracy (mostly <10% error). Assessments involved numerous analyses (n = 57) of a quality control sample over the validation period and the testing of 9 laboratory-prepared and 15 real-life casework samples using an experimental protocol that allowed (a) contemporaneous establishment of a 3-point calibration curve; (b) analysis of negative and positive controls; and (c) analysis of two different samples (in duplicate), all within a single analysis batch of about 4.2 min. The validity and effectiveness of the DART-MS methodology for the quantitation of fentanyl in drug samples were hence demonstrated.