Extraction of THC, Hydroxy-THC and Carboxy-THC from Whole Blood Using ISOLUTE® SLE+ Prior to GC/MS Analysis

Importance of the Topic

Reliable extraction of cannabinoids from whole blood is essential for forensic and clinical toxicology. Δ9-THC and its metabolites 11-hydroxy-THC and 11-nor-9-carboxy-THC are key markers for recent use and metabolic status. Efficient sample preparation minimizes matrix interferences, improves sensitivity, and accelerates throughput in GC/MS analysis.

Study Objectives and Overview

This application note presents a streamlined procedure using ISOLUTE SLE+ supported liquid extraction (SLE+) for isolating THC, THC-OH and THC-COOH from 1 mL whole blood. The protocol targets high recoveries (>74%), low variability (RSD <9%) and compatibility with subsequent GC/MS analysis.

Methodology and Sample Preparation

Whole blood (1.2 mL) is acidified with 0.1% formic acid and mixed. A pretreated volume (800 µL) is loaded onto a 1 mL ISOLUTE SLE+ column. After a 5 min equilibration, analytes are eluted with 3 mL MTBE followed by 3 mL hexane under gravity. The combined eluate is evaporated under air or nitrogen at 40 °C, then derivatized with BSTFA:TMCS (99:1) in ethyl acetate and heated at 70 °C for 25 min.

Used Instrumentation

• Agilent 7890A GC with splitless injection, DB-5 column (30 m x 0.25 mm x 0.25 µm), helium carrier at 1.2 mL/min, oven ramp 60 °C to 350 °C at 25 °C/min.
• Agilent 5975C MS in Selected Ion Monitoring (SIM) mode for target and qualifier ions.
• Biotage SPE Dry or TurboVap for solvent evaporation.

Results and Discussion

The optimized SLE+ procedure yielded recoveries between 72% and 83% for all three analytes, with RSDs below 10%. Calibration curves over 1–150 ng/mL were linear (r2 ≥0.999). Lower limits of quantitation were 1 ng/mL for THC and 3 ng/mL for THC-OH and THC-COOH. Chromatograms showed clear peak separation and minimal matrix background.

Benefits and Practical Applications

• High analyte recovery and reproducibility support reliable quantitation in forensic and clinical settings.
• Absence of emulsions and reduced solvent usage streamline workflow compared to traditional liquid–liquid extraction.
• Compatibility with standard GC/MS instrumentation facilitates implementation in analytical laboratories.

Future Trends and Potential Applications

Emerging trends include automation of SLE+ on high-throughput platforms, coupling with tandem mass spectrometry for enhanced specificity, and extension to additional psychoactive or therapeutic analytes. Miniaturized formats and integration with online sample cleanup may further accelerate turnaround in routine toxicology testing.

Conclusion

The ISOLUTE SLE+ protocol delivers a robust, reproducible method for extracting THC and its key metabolites from whole blood. Excellent recoveries, low variability and straightforward workflow make it a valuable approach for bioanalytical laboratories performing GC/MS drug screening.

Reference

Application Note AN840, Biotage 2015.