Reference measurement procedure for Δ9-tetrahydrocannabinol in serum
An isotope dilution gas chromatography/mass spectrometry (ID-GC/MS) reference measurement procedure for Δ9-tetrahydrocannabinol (THC) in serum was developed and validated. The method complies with the concept of a ratio primary reference measurement procedure. The uncertainty was determined for two concentrations of THC in serum (1 ng/mL and 2.4 ng/mL). The calculation procedure is based on the Guide to the Expression of Uncertainty in Measurement (GUM). The relative expanded uncertainty was found to be less than 2% for both concentration levels, corresponding to a 95% confidence interval. For the reference method, it was shown that the measurement of THC within the concentration range covered by the current threshold values is very accurate. The method has the potential to provide traceability for the methods used in practical forensics.
Validation of the quantitative determination of tetrahydrocannabinol and its two major metabolites in plasma by ultra-high-performance liquid chromatography-tandem mass spectrometry according to the total error approach.
In Belgium, driving under the influence (DUI) of cannabis is prohibited and has severe legal consequences for the driver if the blood plasma concentration of Δ(9)-tetrahydrocannabinol (THC) exceeds 1 µg/L. A method to quantify low concentrations of THC and its hydroxylated (THC-OH) and carboxylated (THC-COOH) metabolites in plasma was developed for DUI but also for other applications. Ultra-high-performance liquid chromatography coupled to mass spectrometry seems to be a very convenient method to combine fast chromatographic separation and good sensitivity. The method was validated according to total error approach. Chromatographic separation was achieved in a 3-min total run time. The limits of quantitation were lower or equal to 1 µg/L for all compounds. The linearity of the method was acceptable in the validated range of concentrations (from 0.5 to 50 µg/L for THC, from 0.9 to 50 µg/L for THC-OH and from 1.1 to 100 µg/L for THC-COOH). The biases were lower than 13%, and the relative standard deviations for repeatability and intermediate precision did not exceed 15%. Lower and upper β-expectation tolerance limits did not exceed the acceptance limits of 20% for concentrations higher than 2 µg/L for THC and THC-OH and higher than 4 µg/L for THC-COOH. The acceptance limits were 30% for THC and THC-OH concentrations lower than 2 µg/L and for THC-COOH concentrations lower than 4 µg/L.
Spin label motion in fatty acids.
Spin labels dissolved in highly purified fatty acid systems exhibit nearly identical tumbling rates in liquid and solid phases. Even though the spin labels do not have the same molecular geometry as the lipid matrix the melting point of the matrix can be inferred by measurements of the temperature dependency of molecular motion.