Cannabinoids standards were purchased from THC Pharm (Frankfurt, Germany) (THC-A, 1 mg/mL methanol; Cannabidiol-A [CBD-A], 1 mg/mL; cannabigerol, 1 mg/mL methanol) and from Lipomed (Arlesheim, Switzerland) (THC, 1 mg/mL methanol; cannabinol [CBN], 1 mg/mL methanol; cannabidiol [CBD], 1 mg/mL methanol). The acetonitrile from Sigma-Aldrich (Steinheim, Germany), methanol from Merck (Darmstadt, Germany), and ethanol and formic acid from Fluka (Buchs, Switzerland) were all of analytical grade.
Three e-cigarettes (iTaste VV type, VV standing for variable voltage from 3.5 to 5 V), clearomizers (CE4+ type, 1.6 mL, 4 long wicks) and liquid refills (DEA Calliope™, Dea Flavour S.R.L., Trento, Italy), with different nicotine contents (nicotine-free, 9 mg/mL and 18 mg/mL) were purchased from local specialized e-cigarette retailers in Lausanne and Yverdon-les-Bains (Switzerland). These e-cigarettes (coil resistance of 3.8 Ω) have been chosen because of their different setting options (power and voltage). For the experiments, the voltage was set at the maximum permitted level (5 V). The composition of the liquid refills was the same for except the nicotine burden: propylene glycol (PG) 60%, vegetal glycerin (VG) 30% and flavors (+nicotine if present) in 10% distilled water.
Preparation of cannabinoid-enriched liquid refills
To study the efficiency of decarboxylation by e-cigarettes, standards of THC-A (50 mg of pure powder) and THC (in ethanolic solution at 100 mg/ml), obtained from Lipomed (Arlesheim, Switzerland), were mixed with liquid refills.
Many users on the Internet have reported performing a decarboxylation step to convert THC-A into its psychoactive THC form. Commercial nicotine-free liquid refills (n = 2) were spiked with pure THC ethanolic solution up to a concentration of 4.3 mg/g of liquid (Design A). Another set of commercial nicotine-free liquid refills (n = 2) were spiked with pure THC ethanolic solution up to a concentration of 4.3 mg/g of liquid and pure THC-A powder up to a concentration of 81 mg/g of liquid (Design B). Finally, a typical cannabis cigarette (“joint”) was prepared according the European practice (Design C): chopped head tops mixed with tobacco (400 mg of tobacco, 400 mg of cannabis at 17% of a total of THC + THC-A, composed of 95% THC-A) were used to generate theoretical cannabinoids quantities similar to those used in the designs A and B. The cannabis used was medical grade cannabis (bedrobinol from Bedrocan BV, Veendam, the Netherlands) with 17% of a total of THC + THC-A and less than 1.0% CBD. The three designs are compiled in Fig. 2.
Figure 2: Decarboxylation experimental protocols.
(1 g of liquid is consumed after about 200 puffs and the described cannabis cigarette is consumed after 15–20 puffs).
To evaluate the efficiency of the decarboxylation step for BHO before vaping, known amounts of decarboxylated (thermally activated) and not decarboxylated (not activated) BHO were dissolved in commercial liquid refills and pure propylene glycol (PG) purchased from Chemnovatic (Lublin, Poland). BHO at 3%, 5% and 10% (w/w) in nicotine-free e-liquid and pure PG was prepared.