Comparison of post-targeted and pre-targeted urine drug screening by UHPLC-HR-QTOFMS

Abstract

The current illicit drug scene, with its unpredictable appearance of new psychoactive substances, challenges drug-testing laboratories. Ultra-high performance liquid chromatography-high-resolution quadrupole time-of-flight mass spectrometry (UHPLC-HR-QTOFMS) provides an especially versatile analytical platform for responding to this continuous change. QTOFMS can be used to collect nonselective MS/MS by broadband data-independent acquisition (DIA), recording all product ions regardless of the precursor ion. Another approach is to collect selective MS/MS by data-dependent acquisition (DDA), using a narrow precursor mass window with preset criteria such as the presence of a particular ion among a precursor ion list. The present study compared methods based on these two modes of data acquisition on a single UHPLC-HR-QTOFMS instrument setup and using identical sample preparation. The DIA method relied on a post-targeted reverse database search and the DDA method on a spectrum library search, each comprising the same selection of 200 drugs of abuse. The performance between the methods was compared in terms of the limit of identification (LOI) and specificity. The median LOI of the DIA method (8 ng/mL) was lower than that of the DDA method (16 ng/mL). Among the 20 model compounds, a better LOI was obtained with DIA for 13 compounds. DIA was superior in resolving closely eluting and co-eluting isomeric and isobaric compounds. Comparison between the feasibility of DIA and DDA for casework was carried out by analyzing 50 authentic case urine samples. DIA produced 266 identifications involving 46 different substances, and DDA produced 225 identifications involving 42 substances. Moreover, substance identification by DIA was more straightforward and the method was easier to deploy in casework. Nonetheless, the DDA approach with substance-specific collision energies produced informative product ion spectra suitable for occasional confirmatory analyses.