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Stability of drugs of abuse in synthetic oral fluid investigated using a simple “dilute and inject” method of analysis

Research output: Contribution to journalArticlepeer-review

Ivana Gavrilović, Alessandro Musenga, Kim Wolff, Alison Woffendin, Andrew Smart, Fan Gong, Duncan Harding, David Cowan

Original languageEnglish
JournalDrug Testing And Analysis
DOIs
Accepted/In press2022

Bibliographical note

Publisher Copyright: © 2022 The Authors. Drug Testing and Analysis published by John Wiley & Sons Ltd.

King's Authors

Abstract

Human oral fluid is well established as a matrix for drug screening, particularly in the workplace. The need to synthesise synthetic oral fluid (SOF) has been recognised in order to overcome human oral fluid's composition variability. We have used SOF spiked with six common drugs of abuse or their primary metabolites: morphine, amfetamine, benzoylecgonine, cocaine, diazepam, and (−)-Δ9-tetrahydrocannabinol (THC) in order to assess the suitability of this matrix for quality assurance purposes. For confirmation of a drug screening test, controls and spiked standards are normally required. All our analytes were detected by LC–MS/MS using a quick and easy “dilute and inject” sample preparation approach as opposed to relatively slower solid-phase extraction. The limit of detection (LOD) was 10 ng/ml for diazepam and THC and 5 ng/ml for morphine, amfetamine, benzoylecgonine and cocaine. Validation results showed good accuracy as well as inter- and intra-assay precision (CV [%] < 5). Our work highlighted the importance of adding Tween® 20 to the SOF and calibrants to reduce losses when handling THC. Furthermore, drug stability was tested at various temperatures (5°C, 20°C and 40°C), for a number of days or after freeze–thaw cycles. Recommendations regarding storage are provided, the spiked SOF being stable at 5°C for up to 1 week without significant drug concentration loss.

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