Elimination of Non-Volatile Sample Matrix Components After GC Injection using a Thermal Desorber and Microvial Inserts

Significance of the Topic

Gas chromatography analysis of samples containing non-volatile matrix components typically requires extensive cleanup to avoid contamination of the injection port and column and to maintain analyte integrity and quantitation accuracy. The elimination of matrix residues is crucial for high-throughput laboratories in pesticide residue analysis, environmental monitoring, and petrochemical quality control.

Study Objectives and Overview

The study presents an automated thermal desorption approach using disposable glass microvial inserts for direct liquid injection of complex, “dirty” samples into a GC system. Objectives include demonstrating effective solvent removal, minimizing matrix carryover, and achieving reproducible analyte transfer to the column without extensive sample preparation.

Methodology

The procedure employs a thermal desorber (TDU) equipped with glass microvials placed in transport adapters, coupled to a cooled programmable temperature vaporization (PTV) inlet for analyte refocusing. Sample types include QuEChERS-prepared vegetable extracts spiked with 44 pesticides, motor oils spiked with gasoline, used motor oil, and olive oil. Automated injections (MPS 2 robotic sampler) or manual sampling introduce precise volumes into microvials. Key steps:

• Solvent venting under controlled conditions to remove extraction solvent without losing analytes.
• Temperature ramp to transfer analytes onto the GC column while retaining non-volatile matrix in the microvial.
• Disposable microvial replacement between runs to prevent contamination and carryover.

Instrumentation Used

• Agilent 6890 GC with 5975 mass selective detector
• GERSTEL TDU thermal desorption unit with glass microvial inserts
• GERSTEL CIS 4 PTV inlet
• GERSTEL MPS 2 autosampler
• HP-5MS column (30 m × 0.25 mm × 0.25 μm)

Main Results and Discussion

• Pesticide analysis in QuEChERS vegetable extracts exhibited high reproducibility (compound area RSDs 2–12 %) and no detectable carryover on reanalysis.
• Overlayed chromatograms of standard and spiked extracts showed equivalent peak responses at 10 ppb, confirming minimal matrix effects.
• Motor oil spiked with 0.5 % gasoline delivered well-resolved GRO peaks using the microvial approach, compared to poor resolution from direct inlet injection.
• Used motor oil analysis detected residual gasoline-range organics, illustrating method sensitivity for environmental contaminants.
• Extra virgin olive oil profiling identified key volatile compounds (e.g., hexenal, nonanal, farnesene) without inlet fouling or carryover.

Benefits and Practical Applications

This technique significantly reduces sample preparation time and solvent use, delivers robust chromatographic performance for “dirty” and viscous matrices, and extends the lifetime of inlet liners and columns. Its automation capability enhances throughput in pesticide residue testing, petroleum analysis, and food flavor profiling.

Future Trends and Applications

• Integration with high-resolution MS and real-time data analytics to expand target compound libraries.
• Adaptation for on-line monitoring and process control in industrial environments.
• Development of miniaturized microvial designs for lower sample volumes and increased sensitivity.
• Extension to other challenging matrices such as biofluids, wastewater, and polymers.

Conclusion

The disposable microvial thermal desorption approach enables direct GC analysis of complex, non-volatile matrices with minimal cleanup, excellent reproducibility, and no carryover. Automated solvent removal and analyte focusing streamline workflows and protect GC inlet and column integrity, making it a versatile tool for advanced analytical laboratories.

Reference

• Maštovská K, Lehotay SJ, Anastassides M. Anal Chem. 2005;77:8129–8137.
• Lehotay SJ, Lightfield AR, Harmon-Fetcho JA, Donoghue DJ. J Agric Food Chem. 2001;49:4589–4596.
• Cajka T, Maštovská K, Lehotay SJ, Hajslova J. J Sep Sci. 2005;28:1048–1060.