Absorptive stripping voltammetry for cannabis detection

BACKGROUND: Given that Δ(9)-tetrahydrocannabinol, the active constituent of cannabis, has been shown to greatly reduce driving ability, thus being linked to many drug driving accidents, its reliable detection is of great importance. RESULTS: An optimised carbon paste electrode, fabricated from graphite powder and mineral oil, is utilised for the sensitive detection of Δ(9)-tetrahydrocannabinol (THC) in both aqueous solutions of pH 10.0 and in synthetic saliva solutions. “Absorptive Stripping Voltammetry” is exploited to that effect and the paste is used to pre-concentrate the carbon paste electrode with the target molecule. Practical limits of detection of 0.50 μM and 0.10 μM are determined for THC in stationary and stirred aqueous borate buffer solutions, respectively. Theoretical limits of detection are also calculated; values of 0.48 nM and 0.41 nM are determined for stationary and stirred THC aqueous borate buffer solutions, respectively. THC concentrations as low as 0.50 μM are detected in synthetic saliva solutions. The sensitivity of the sensor was 0.12 μA μM(−1), 0.84 μA μM(−1) and 0.067 μA μM(−1) for the stationary buffer, the stirred buffer and the saliva matrix, respectively. CONCLUSIONS: “Absorptive Stripping Voltammetry” can be reliably applied to the detection of Δ(9)-tetrahydrocannabinol, after suitable optimisation of the assay. Usefully low practical limits of detection can be achieved.