J Anal Toxicol. 2021 Jun 17:bkab074. doi: 10.1093/jat/bkab074. Online ahead of print.
In late 2019 the National Laboratory Certification Program (NLCP) published an article reporting on the potential analytical conversion of 7-carboxy-cannabidiol (CBD-COOH) to 11-nor-9-carboxy-Δ9-tetrahydrocannabinol-9-carboxylic acid (THC-COOH) in urine samples. (1) The same conversion is possible in oral fluid with the parent analyte cannabidiol (CBD) converting to Δ9-tetrahydrocannabinol (Δ9-THC) and Δ8-tetrahydrocannabinol (Δ8-THC) under strong acidic conditions. With the recent rise in states legalizing the use of THC and the availability of products containing only CBD, unless the analytical in vitro conversions are controlled, the detection of Δ9-THC or Δ8-THC in oral fluid may not clarify whether the donor was using a CBD product, licit or illicit THC product. Authentic oral fluid samples submitted for cannabinoid analysis were subjected to multiple sample preparation procedures and extraction methods to determine the conditions that allow CBD to convert to THC. CBD single analyte controls prepared from a certified THC-free source were added to the batch to monitor the rate of conversion. Samples were prepared using a base hydrolysis, solid phase extraction, derivatization, and analysis by liquid chromatography with tandem mass spectrometry (LC-MS-MS). The base hydrolysis and derivatization were tested independently and did not contribute to the conversion rate. Adjusting the pH of the sample preparation and extraction from pH 2.0 to pH 5.0 changed the conversion rate from 5% to 1%. A pH of 6.0 was not strong enough to extract the cannabinoids efficiently. Removing the acid component of the preparation and extraction procedure eliminated the conversion to THC; however, this did reduce the analyte recovery depending on which extraction column was used. Processing time also contributed to the conversion rate. With smaller trial runs, conversion was not always seen but with larger validation batches low level conversion of 1-2% was observed. A fully validated LC-MS-MS method utilizing solid-phase extraction was developed for CBD, Δ9-THC, Δ8-THC, and cannabinol (CBN). The method specifically targets those analytes found in oral fluid after CBD administration and those that are seen during in vitro CBD conversion. CBD administration was performed using a certified THC-free CBD control.