A comparison of developed and validated chromatographic methods (HPLC, GC-MS) for determination of delta-9-tetrahydrocannabinol (Δ9- THC) and delta-9-tetrahydrocannabinolic acid (Δ9-THCA-A) in hemp

Abstract

The aim of this study was to develop and validate chromatographic methods for determination of Δ9-THC and Δ9-THCA-A in hemp and to compare the quantitative results obtained by GC-MS with the quantification results obtained by HPLC. 0.5 g samples of dry plant material were extracted with 5 ml methanol overnight (16 h). The separation of the sample components was performed by HPLC on an RP-18e Chromolith column (5 μm, 100 mm) at 40°C with isocratic elution. The mobile phase consisted of a mixture of water containing 100 μl phosphoric acid per 1 litre (pH 3) and acetonitrile (70:30). GC-MS separation of sample components was carried out on an HP-5MS (30 m x 0.25 mm x 0.25 μm) column. Acquisition was performed in the full scan mode. The limits of detection (LOD) for HPLC were 0.00030% (converted to dry hemp matter) for Δ9-THC and 0.00068% for Δ9-THCA-A. The calibration curves were linear both for Δ9-THC and THCA-A (r = 0.999) in the tested range: 0.05% (2.5 μg/ml) up to 2.0% (100 μg/ml). The intra-assay and inter-assay precision, expressed as the percentage coefficient of variation (CV), were 3.5% and 8.2% for Δ9-THC, and 3.4% and 8.4% for Δ9-THCA-A, respectively. The limit of detection (LOD) for Δ9-THC obtained by GC-MS was 0.015%. The calibration curve was linear (r = 0.998) in the range from 0.1% up to 0.8%. The GC-MS intra-assay precision expressed as CV was 15.3% and the inter-assay precision was 21.3%. Comparison of the Δ9- THC quantitative results obtained for the real hemp samples by the two methods shows that there is a good correlation between them (r = 0.99) and proves that it is possible to apply them when measuring the total Δ9-THC concentration in cannabis hemp and other cannabis products e.g. cannabis resin (hashish). The results of the study show that both developed methods can be used in routine analysis for distinguishing drug type from fibre type cannabis. © by the Institute of Forensic Research.