Recovery of spiked Δ9-tetrahydrocannabinol in oral fluid from polypropylene containers

Abstract

Oral fluid is currently used by Australian and international law enforcement agencies and employers to detect recent use of cannabis and other drugs of abuse. The main psychoactive constituent of cannabis, ∆ 9 -tetrahydrocannabinol (THC), is highly lipophilic and losses occur when in contact with plastic, possibly due to its adsorption onto the plastic surface. This study aims to investigate factors governing the interaction of THC with plastic and search for ways of overcoming such interaction so to improve THC recovery. As polypropylene is one of the most common types of plastic used in collection devices, it was the focus of this study.All experiments were done by preparing neat oral fluid samples spiked with THC in 2-mL polypropylene centrifuge tubes. Samples were transferred with or without prior addition of Triton ® X-100 (0.25%) to glass tubes containing d 3 -THC as internal standard and 0.1 M phosphate buffer was then added. Samples were extracted by liquid-liquid extraction using hexane/ethyl acetate (9:1 v/v), dried and analysed by gas chromatography-mass spectrometry (GC-MS) after derivatisation. No significant difference was found in terms of THC loss to plastic when the concentration ranged from 25-1000 ng/mL in the same volume of oral fluid.Varying the oral fluid volume (0.5-1.5 mL) while keeping THC at a constant concentration showed an upward trend with more loss associated with lower volumes. The use of Triton ® X-100 significantly decreased the adherence of THC to the plastic tubes and increased the THC transfer (>96%) at all volumes tested. Degradation of THC during storage was also studied over a 4-week period and it was found that azide did not seem to play a significant role in preserving THC in oral fluid.

Techniques and Technologies for The Bioanalysis of Sativex ® , Metabolites and Related Compounds

“…This improves cannabinoid stability compared with neat oral fluid samples, though refrigerated storage and analysis within a few weeks is still recommended for samples collected using the Quantisal, StatSure and Oral-Eze devices [107,108]. THC in expectorated oral fluid diluted with phosphate buffer at a pH of approximately 6 was stable for 3 weeks when refrigerated, while samples diluted with Cozart DDS buffer solution was stable for at least 4 weeks at room temperature [109].…”

“…In addition to losses through degradation, THC is known to be highly lipophilic, commonly resulting in adsorptive losses to precipitants and surfaces during storage or sample preparation [109,110]. CBD is also lipophilic [110] and is likely subject to similar effects.…”

“…Jagadeo et al [44] added acetonitrile to blood samples to desorb any cannabinoids from the container walls during their sample preparation. Addition of a nonionic surfactant has also been shown to reduce the degree of adsorption of THC to polypropylene surfaces in neat oral fluid samples [109].…”

Current knowledge on cannabinoids in oral fluid

“…In fortified expectorated OF samples centrifuged for 10 min, only 28.8% THC was recovered from supernatant; 51.7% was recovered from protein pellet and 14.7% from the polypropylene tube after addition of surfactant Triton ® X-100. [181] Mucus in neat OF prevented good interaction with sorbent material during solid phase extraction, reducing drug concentrations and increasing imprecision. [150] Dry mouth following cannabis smoking also makes expectoration difficult and often yields low sample volumes.…”

“…[209] THC loss (22.8-29.3%) from adsorption to polypropylene tubes was similarly observed by Molnar et al; this loss was minimized by addition of surfactant Triton ® X-100 with > 96% THC recovery. [181] Moreover, fortified OF samples in phosphate buffer with and without preservative sodium azide showed a similar THC loss of approximately 25% at 4°C and 50% at room temperature after 4 weeks, suggesting that oxidative degradation may contribute more to OF THC instability than microbial action. [181] The Cozart ® fortified OF samples had minimal loss even at room temperature over 4 weeks.…”