Simplifying Non-Target Analysis: Improving Peak Match Confidence with Gas Chromatography, High Resolution-TOFMS and Improved Data Processing Strategies

Importance of the Topic

Non-target analysis of complex environmental and industrial samples has historically relied on targeted methods, limiting the discovery of unexpected compounds. Advances in gas chromatography combined with high resolution time-of-flight mass spectrometry (HR-TOFMS) and improved data processing enable comprehensive screening of unknowns. This approach enhances detection capabilities and identification confidence, supporting more thorough environmental monitoring, quality assurance and research workflows.

Objectives and Study Overview

This study evaluated a non-targeted workflow using LECO's Pegasus GC-HRT+ 4D platform within the EPA ENTACT multi-lab trial. Blind samples spiked with 100–400 compounds were analyzed to assess the performance of combined EI and CI ionization modes across one-dimensional (1D) and comprehensive two-dimensional gas chromatography (GCxGC). The goal was to demonstrate improved peak deconvolution, identification accuracy and review efficiency via a novel Identification Grading System (IGS).

Methodology

Samples were analyzed using both 1D GC and GCxGC separations. Electron ionization (EI) and methane-ammonia chemical ionization (CI) modes were employed to confirm molecular ions. High acquisition rates and a mass range of 29–1000 m/z captured detailed high-resolution accurate mass spectra. Data processing utilized HRD® deconvolution and library searching, followed by scoring criteria based on spectral similarity, mass accuracy, retention index matching and CI confirmation to assign confidence tiers (A, B or X).

Used Instrumentation

• Gas chromatograph: LECO Pegasus GC-HRT+ 4D
• Ionization: EI at 250 °C and CI (CH4 + 5 % NH3) at 200 °C
• High-resolution TOFMS: ≥ 25 000 FWHM at m/z 219
• Columns: Rxi-5MS and Rxi-17Sil MS in GCxGC configuration
• Carrier gas: Helium, constant flow 1.4 mL/min
• Data software: ChromaTOF® with High Resolution Deconvolution and Identification Grading System

Main Results and Discussion

GCxGC separations dramatically improved peak resolution and enabled effective deconvolution of coeluting compounds, resulting in higher spectral fidelity and match scores. The addition of CI data allowed confirmation of molecular ions when EI spectra lacked clear molecular peaks. The IGS filter rapidly prioritized high-confidence matches, reducing manual review time from hours to seconds. In blinded EPA trials, the system identified on average 85 % of spiked compounds present in NIST 2017, increasing to 92 % after unblinded review.

Benefits and Practical Applications

• Enhanced non-target screening sensitivity and specificity in environmental and industrial analyses
• Efficient data review via automated confidence scoring, reducing analyst workload
• Reliable identification in complex matrices without extensive custom scripting
• Integration with established spectral libraries and retention index databases

Future Trends and Applications

Continuous improvements in mass spectrometer resolution and acquisition speed will expand non-target analysis capabilities. Integration of machine learning for spectrum interpretation, dynamic library enrichment and real-time monitoring are emerging trends. Broader adoption of automated grading systems and standardized workflows will facilitate large-scale environmental and metabolomic studies.

Conclusion

Combining GCxGC with high-resolution TOFMS and advanced data processing, including an automated identification grading system, significantly enhances non-target compound detection and identification confidence. This workflow streamlines analysis of complex samples and supports robust environmental and quality-control applications.

References

• EPA ENTACT Multi-lab Trial
• NIST 2017 Mass Spectral Library