What is Identification? Comprehensive Characterization of Exposome Samples via GC×GC High Resolution TOFMS

Significance of the Topic

Recent advances in comprehensive exposome analysis are crucial for detecting both expected and emerging environmental contaminants. The integration of two-dimensional gas chromatography (GC×GC) with high-resolution accurate mass time-of-flight mass spectrometry (HRAM-TOFMS) dramatically enhances chromatographic peak separation and spectral fidelity. This capability supports non-targeted screening in complex matrices, addressing the limitations of traditional targeted methods.

Goals and Study Overview

This study evaluated the performance of the LECO Pegasus GC-HRT+ 4D platform in a two-phase exposome project commissioned by the U.S. EPA. Phase 1 involved a blinded analysis of ten standard mixtures (100–400 compounds each) to assess peak detection and identification efficiency. Phase 2 extended the evaluation to three real-world matrices (serum, wristband, dust) spiked with the same standards.

Methodology and Instrumentation

• Gas chromatograph: LECO GC×GC system with primary Rxi-5MS (30 m×0.25 mm×0.25 µm) and secondary Rxi-17Sil MS (0.6 m×0.25 mm×0.25 µm) columns.
• Modulation period: 4 s; primary oven: 40 °C→330 °C (10 °C/min) with 30 min hold; secondary oven offset +15 °C.
• Mass spectrometer: LECO Pegasus GC-HRT+ 4D, EI at 250 °C and CI (CH₄+5% NH₃) at 200 °C.
• Acquisition: 25,000 FWHM at m/z 219; mass range EI 29–1000, CI 60–1000; rate 200 spectra/s (GC×GC) and 6 spectra/s (GC).
• Injection: 1 µL (10:1 DCM dilution), split 10:1 (CI splitless); He carrier at 1.4 mL/min.
• Data processing: ChromaTOF® software with High Resolution Deconvolution® and Identification Grading System (tiers A, B, X) based on spectral similarity, mass accuracy, and retention index.

Main Results and Discussion

• Phase 1 (blinded): average detection of ~85% of spiked compounds with spectra in NIST 17; increased to ~92% after unblinding.
• GC×GC resolved coeluted peaks undistinguishable by 1D GC, enabling clean deconvolution and high match confidence (forward scores >700, mass accuracy ±5 ppm).
• Phase 2 results showed lower recoveries in serum and wristband samples (<40% success blind, <53% unblinded) likely due to extraction inefficiencies and low analyte levels; dust samples performed slightly better.
• Inclusion of CI spectra aided confirmation of molecular ions when EI signals were weak or absent.

Benefits and Practical Applications

• Enhanced sensitivity (10×) and chromatographic resolution enable reliable non-target screening in environmental and biological matrices.
• HRAM data allows accurate molecular formula calculation for both molecular and fragment ions.
• The Identification Grading System offers a transparent confidence metric, facilitating regulatory reporting and interlaboratory comparisons.
• The curated high-resolution mass library from ToxCast compounds expands identification coverage for emerging contaminants.

Future Trends and Opportunities

Continued integration of larger accurate mass libraries and improved extraction protocols will further boost non-targeted exposome characterization. Automation in data processing and machine-learning–driven deconvolution criteria promise to reduce manual review time. Expansion into real-time monitoring and miniaturized sampling could extend applications to field screening and personalized exposure assessment.

Conclusion

The combination of GC×GC separation and HRAM-TOFMS with advanced deconvolution software delivers a powerful platform for comprehensive exposome analysis. High success rates in standard mixtures and insights into matrix effects in biological and environmental samples underscore its utility in non-targeted contaminant screening.

References

• No external references provided in the source text.