Forensic Toxicology Analysis of Non-derivatized Drugs in Urine by Automated Solid Phase Microextraction (SPME) GCxGC-TOFMS

Importance of the Topic

Non-derivatized drug screening in urine is critical for forensic toxicology and clinical testing. Traditional workflows often require labor-intensive derivatization steps to improve volatility and detectability. Automated solid phase microextraction (SPME) combined with comprehensive two-dimensional gas chromatography and time-of-flight mass spectrometry (GC×GC-TOFMS) offers a streamlined approach to achieve high sensitivity, resolution, and throughput while minimizing sample preparation time.

Objectives and Study Overview

• Demonstrate the detectability of ten non-derivatized drugs of abuse in urine using automated SPME-GC×GC-TOFMS.
• Evaluate calibration linearity over 10–1000 ng/mL for forensic screening purposes.
• Illustrate advantages of multidimensional chromatography and TOFMS deconvolution in complex biological matrices.

Instrumentation

• GC×GC-TOFMS: LECO® Pegasus 4D with dual-stage thermal modulator and secondary oven, Agilent 7890 primary GC.
• Autosampler/Prepstation: Gerstel MPS2 with SPME agitator and fiber conditioning station.
• SPME Fiber: 50/30 µm DVB/Carboxen™/PDMS StableFlex.
• Columns: Primary Rxi-5ms (30 m×0.25 mm×0.25 µm), secondary Rtx-200 (1.5 m×0.18 mm×0.18 µm).
• Software: LECO ChromaTOF for acquisition, deconvolution, and calibration.

Methodology

Urine samples were spiked with a ten-component drug mixture at 10, 50, 250, 500, and 1000 ng/mL. Hexachlorobenzene (500 ng/mL) served as internal standard. Automated SPME extraction was performed at 37 °C, 200 rpm for 30 min, followed by thermal desorption at 270 °C. GC ramps: primary oven from 40 °C to 290 °C at 6 °C/min; secondary from 50 °C to 300 °C at 6 °C/min. Modulation period was 5 s, carrier gas helium at 1.5 mL/min. MS range m/z 45–550, acquisition rate 200 spectra/s.

Main Results and Discussion

• Ten drugs (methamphetamine, cocaine, diacetylmorphine, codeine, oxycodone, ecstasy, acetylcodeine, monoacetylmorphine, hydrocodone, LSD) were identified by NIST library matches >75%.
• Over 9000 peaks per sample (S/N ≥50) highlighted matrix complexity and the power of GC×GC separation.
• Calculated relative limits of detection for seven analytes ranged from 0.038 ng/mL (cocaine) to 9.83 ng/mL (LSD).
• Calibration curves achieved ≥90% linearity for nine drugs, with extended-range calibration and peak-combine features to address peak tailing and saturation.
• TOFMS deconvolution enabled accurate identification of co-eluting compounds within 40 ms timeframes.

Benefits and Practical Applications

• Eliminates derivatization, reducing sample handling and analysis time.
• Automated SPME increases reproducibility and throughput.
• GC×GC enhances chromatographic resolution in complex biological matrices.
• High-speed TOFMS provides robust deconvolution for trace-level drug identification.

Future Trends and Opportunities

• Expansion to broader panels including emerging synthetic drugs and metabolites.
• Integration of high-resolution MS with GC×GC for improved specificity.
• Development of novel SPME fiber materials to target polar and thermally labile compounds.
• Advanced data analytics and machine learning for automated library matching and quantitation.
• Field-deployable SPME-GC×GC systems for on-site forensic and clinical screening.

Conclusion

Automated SPME-GC×GC-TOFMS enables sensitive and reliable screening of non-derivatized drugs in urine at ppb levels. The combination of minimal sample preparation, enhanced chromatographic separation, and rapid TOF mass spectral acquisition offers a robust platform for forensic toxicology, clinical toxicology, and QA/QC laboratories.

References

• John Heim. Forensic Toxicology Analysis of Non-derivatized Drugs in Urine by Automated SPME GC×GC-TOFMS. LECO Corporation, 2008.