Drug Screening in Non-Derivatized Urine by Automated Solid Phase Microextraction (SPME) and Comprehensive Multidimensional Gas Chromatography Time-of-Flight Mass Spectrometry (GCxGC-TOFMS)

Importance of the Topic

This work addresses the need for rapid, reliable screening of drugs of abuse in urine without time-consuming derivatization. Automated solid phase microextraction (SPME) combined with comprehensive two-dimensional gas chromatography time-of-flight mass spectrometry (GCxGC-TOFMS) offers enhanced separation, sensitivity, and full-mass-range detection, making it highly valuable in forensic and clinical toxicology workflows.

Objectives and Study Overview

The study aimed to demonstrate the detectability of ten non-derivatized drugs in complex urine matrices, to establish calibration linearity over 10–1000 ng/mL, and to highlight the practical advantages of automated SPME-GCxGC-TOFMS for forensic drug screening.

Methodology and Instrumentation

Sample Preparation and Extraction:

• Urine aliquots (8 mL) spiked with multi-drug standards; hexachlorobenzene added as internal standard (500 ng/mL).
• Automated SPME using a Gerstel MPS2 autosampler with a SPME prep station.
• SPME fiber: 50/30 µm DVB/Carboxen™/PDMS; extraction at 37 °C for 30 min, agitation at 200 rpm.

Chromatographic and MS Conditions:

• GCxGC: Agilent 7890 GC with dual jet thermal modulator coupling a non-polar primary column (30 m × 0.25 mm i.d. × 0.25 µm, Rxi-5MS) to a polar secondary column (1.5 m × 0.18 mm i.d. × 0.20 µm, Rtx-200).
• Temperature programs: primary oven 40 °C (2 min)→6 °C/min→290 °C (10 min); secondary oven 50 °C (2 min)→6 °C/min→300 °C (10 min).
• Thermal modulator: 5 s modulation period with hot pulse (0.8 s) and cool time (1.7 s).
• Carrier gas: helium at 1.5 mL/min constant flow; splitless injection at 260 °C.
• Mass spectrometry: LECO Pegasus 4D TOFMS; mass range m/z 45–550; acquisition 200 spectra/s; ion source 230 °C; electron energy −70 eV; detector voltage 1650 V.

Used Instrumentation

• Gerstel MPS2 autosampler with SPME prep station
• Agilent 7890 gas chromatograph
• LECO dual-stage thermal modulator
• LECO Pegasus 4D TOF mass spectrometer

Main Results and Discussion

The method successfully identified ten target analytes (methamphetamine, cocaine, diacetylmorphine, codeine, oxycodone, ecstasy, acetylcodeine, monoacetylmorphine, hydrocodone, and LSD) with NIST library matches above 75%. Key findings include:

• Calibration curves exhibited linearity (r > 0.90) for nine drugs across 10–1000 ng/mL.
• Over 9000 chromatographic peaks were detected with signal-to-noise ≥ 50.
• Deconvolution of co-eluting peaks, exemplified by hydrocodone, demonstrated accurate spectral extraction within 40 ms, yielding a library similarity of 893.

Benefits and Practical Applications

• Eliminates derivatization step, reducing sample preparation time and potential error.
• Enhanced chromatographic peak capacity and resolution from two-dimensional separation.
• High-speed, full-mass-range TOFMS acquisition enables reliable deconvolution in complex matrices.
• Trace-level detection (ppb) suitable for forensic and clinical toxicology screening.

Future Trends and Possibilities for Application

Ongoing developments may include:

• Validation under forensic toxicology guidelines and accreditation standards.
• Extension to broader panels of emerging drugs and metabolites.
• Integration with laboratory information management systems for high-throughput screening.
• Advances in real-time data deconvolution and software automation.
• Miniaturized or in-field SPME devices paired with portable GCxGC-TOFMS platforms.

Conclusion

Automated SPME coupled with GCxGC-TOFMS provides a robust, sensitive, and streamlined approach for non-derivatized drug screening in urine. The method achieves high linearity, excellent spectral integrity, and rapid detection of trace analytes in complex biological matrices, offering significant advantages for forensic and clinical laboratories.