A preliminary investigation on the distribution of cannabinoids in man

Simultaneous quantification of free and glucuronidated cannabinoids in human urine by liquid chromatography tandem mass spectrometry

BACKGROUND

Cannabis is the most commonly abused drug of abuse and is commonly quantified during urine drug testing. We are conducting a controlled drug administration study investigating efficacy of urinary cannabinoid glucuronide metabolites for documenting recency of cannabis intake and for determining stability of urinary cannabinoids.

METHODS

A liquid chromatography tandem mass spectrometry method was developed and validated quantifying Δ9-tetrahydrocannabinol (THC), 11-hydroxy-THC (11-OH-THC), 11-nor-9-carboxy-THC (THCCOOH), cannabidiol, cannabinol, THC-glucuronide and THCCOOH-glucuronide in 0.5 ml human urine via supported-liquid extraction. Chromatography was performed on an Ultra Biphenyl column with a gradient of 10 mmol/l ammonium acetate, pH 6.15 and 15% methanol in acetonitrile at 0.4 ml/min. Analytes were monitored by positive and negative mode electrospray ionization and multiple reaction monitoring mass spectrometry.

RESULTS

Linear ranges were 0.5-50 ng/ml for THC-glucuronide, 1-100 ng/ml for THCCOOH, 11-OH-THC and cannabidiol, 2-100 ng/ml for THC and cannabinol, and 5-500 ng/ml for THCCOOH-glucuronide (R(2)>0.99). Mean extraction efficiencies were 34-73% with analytical recovery (bias) 80.5-118.0% and total imprecision 3.0-10.2% coefficient of variation.

CONCLUSION

This method simultaneously quantifies urinary cannabinoids and phase II glucuronide metabolites, and enables evaluation of urinary cannabinoid glucuronides for documenting recency of cannabis intake and cannabinoid stability. The assay is applicable for routine urine cannabinoid testing.

Isomerization of cannabidiol and Δ9-tetrahydrocannabinol during positive electrospray ionization. In-source hydrogen/deuterium exchange experiments by flow injection hybrid quadrupole-time-of-flight mass spectrometry

RATIONALE

Liquid chromatography/tandem mass spectrometry (LC/MS/MS) is frequently used for analysis of cannabinoids in drug abuse control. Despite differences in structure, the isomers Δ(9) -tetrahydrocannabinol (THC) and cannabidiol (CBD) provide identical fragment spectra after positive electrospray ionization (ESI). For elucidation of the reason, hydrogen/deuterium (H/D) exchange experiments were performed.

METHODS

Solutions of THC and CBD in D(2) O/acetonitrile (50:50, v/v) were flow-injected into acetonitrile as the mobile phase and measured by hybrid quadrupole-time-of-flight mass spectrometry (FI-QTOF-MS) in targeted MS/MS mode. The MS and collision-induced dissociation (CID) spectra at 10, 20 and 40 eV were interpreted with respect to number and position of exchanged hydrogen atoms. For comparison the same measurements were preformed in H(2) O, after addition of 0.5% formic acid and with negative ESI.

RESULTS

Depending on injected volume and position in the response curve, up to 7 or 8 hydrogen atoms were exchanged by deuterium in THC or CBD. Positive ESI CID spectra were available for precursors with up to 4 exchanged D-atoms and showed that besides the OH groups also an H/D exchange at carbon atoms of the non-aromatic part of the molecules occurred for both THC and CBD. After negative ESI, no H/D exchange in addition to the OH groups and different CID spectra of both substances was found.

CONCLUSIONS

Injection of the investigated substances in D(2) O and measurement by FI-QTOF-MS proved to be an efficient way to perform H/D exchange experiments. The results were interpreted as an acid-catalyzed in-source equilibration between THC and CBD leading to the same precursor ions and to an H/D exchange in the methyl groups under the increased acidic conditions in the positive ESI droplets. Therefore, in positive LC/ESI-MS/MS, peak identification by CID spectra or by abundance ratio of multiple reaction monitoring (MRM) transitions is not sufficient for unambiguous discrimination between THC and CBD and must be supported by retention time or other experimental evidence.