In-Liner Derivatisation and LVI-GC-MS of THC in Human Hair

Importance of the Topic

Hair analysis of drugs provides a non-invasive way to monitor long-term substance exposure and usage patterns. Detecting delta-9-tetrahydrocannabinol (THC) and its metabolite THC-COOH in human hair is especially valuable in forensic toxicology, clinical monitoring, workplace testing, and doping control, offering an extended detection window compared with blood or urine.

Study Objectives and Overview

This application note explores a streamlined workflow that integrates in-liner derivatisation directly in the GC injection port with large volume injection–gas chromatography–mass spectrometry (LVI-GC-MS). The goals are to simplify sample preparation, reduce solvent consumption and solid-phase extraction steps, and improve detection limits for THC and THC-COOH in hair extracts.

Instrumentation Used

• Programmable injector: ATAS Optic 2-200 operating in expert mode
• Gas chromatograph: Agilent 6890 equipped with SGE BP-1 column (50 m × 0.32 mm i.d., 0.25 µm film)
• Mass spectrometer: Agilent 5973 MSD in selected ion monitoring (SIM) mode

Methodology

The key steps of the method are:

• Extract hair samples in ethyl acetate.
• Inject 125 µL of extract into the programmable injector; vent solvent under split conditions to remove excess matrix.
• Add 2 µL of BSTFA derivatisation reagent under static flow.
• Raise injector temperature to 330 °C for in-liner derivatisation.
• Apply pressure ramp to transfer derivatised analytes onto the column in splitless mode.
• Separate analytes using a 10 °C/min oven ramp from 80 °C to 260 °C (hold 5 min).
• Detect target ions in SIM: THC (m/z 371, 386, 303) and THC-COOH (m/z 371, 473, 488).

Key Results and Discussion

Comparative experiments demonstrated that large volume injection with on-line derivatisation provides substantial signal enhancement versus conventional 1 µL splitless injection of pre-derivatised standards. Chromatograms exhibit higher peak abundance and reduced noise level (see Figure 2), enabling lower limits of quantification. The programmable injector ensures reproducible reagent addition and efficient transfer of derivatives.

Benefits and Practical Applications

This in-liner derivatisation approach:

• Eliminates separate derivatisation vials and manual handling of reagents.
• Reduces total sample preparation time and solvent usage.
• Enhances sensitivity and lowers detection limits for trace analysis in hair.
• Is compatible with automated autosamplers for high-throughput workflows.

Future Trends and Opportunities

Further developments may include:

• Extension of LVI in-liner derivatisation to other drug classes and polar metabolites.
• Integration with robotic autosamplers for multiplexed derivatisation protocols.
• Adoption of high-resolution mass spectrometry to achieve broader screening capabilities.

Conclusion

The combination of in-liner derivatisation using a programmable injector and large volume injection GC-MS offers an efficient, sensitive, and automation-friendly approach for THC and THC-COOH analysis in hair. This methodology streamlines workflows, reduces consumables, and provides robust performance suitable for forensic and clinical laboratories.