Comparison of Extraction Methods for 11-Nor-Delta-9-Tetrahydrocannabinol-9-Carboxylic Acid (Thc-Cooh) in Urine Samples Prior to GC-MS Analysis
The Bulletin of Legal Medicine,
Vol. 21 No. 1 (2016)
Objective: Marijuana is the most widely used illegal substance in the world. The target analyte for cannabinoids analysis in urine is THC-COOH. The most widely used sample preparation methods for THC-COOH are liquid-liquid extraction (LLE) and solid phase extraction (SPE). The aim of this work is to compare the extraction methods (LLE and SPE) for (±)-ll-nor-9-carboxy-A9-THC ÇTHC-COOH) for synthetic urine samples (n=80) prior to Gas Chromatography Mass Spectrometry (GC-MS) analysis. In addition, a method validation was conducted in terms of reproducibility, selectivity, accuracy, precision and linearity.
Materials and Methods: (±) -1 l-nor-9-carboxy-A ’-THC and (±) -ll-nor-9-carboxy-A9-THC-D3 (as the internal standard) were used in the studies. Toxi tube B and Clean Screen THC cartridges were used for LLE and SPE, respectively. BSTFA with 1% TMCS were used in the derivatization step. The analysis is performed with Thermo Finnigan Trace GC-MS. Minitabll was used in statistical evaluations.
Results: The limit of detection (LOD) was found to be 2 pg/L. All recovery values were >90% with RSD values <10%. A calibration curve for the standard stock solutions of 25-500 pg/L was obtained with a coefficient of variation (R2) of 0.9968 which indicates a good linearity. The Anderson-Darling test applied indicated that, LLE and SPE results do not follow a normal distribution, therefore, a non-parametric test, Wilcoxon signed-rank test was used in statistical evaluations.
Conclusions: The linearity, repeatability and recovery values obtained in the study were found to be in accordance with bioanalytical validation criteria. According to the statistical results obtained, a significant difference between LLE and SPE was found (p <0.005). By means of this study, the importance of sample preparation steps prior to analysis has been shown.
Keywords: TCH-COOH, Liquid-Liquid Extraction, Solid Phase Extraction, Urine, Gas Chromatography Mass Spectrometry.
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