BOOSTING NON-TARGETED ANALYSIS WITH COMPREHENSIVE TWO- DIMENSIONAL GAS CHROMATOGRAPHY AND HIGH-RESOLUTION MASS SPECTROMETRY

Significance of the Topic

Non-targeted analysis in environmental chemistry enables comprehensive detection of known and unknown contaminants. Combining comprehensive two-dimensional gas chromatography (GC×GC) with high-resolution time-of-flight mass spectrometry (HR-TOFMS) enhances separation power and mass accuracy, crucial for assessing pollutant profiles in sensitive regions like the Arctic.

Objectives and Study Overview

The study aimed to demonstrate the advantages of GC×GC in both targeted and non-targeted screening workflows, evaluate the complementary roles of electron ionization (EI) and electron capture negative ionization (ECNI), and improve confidence in compound annotation applying these methods to glaucous gull liver extracts from Svalbard.

Instrumentation

GC×GC-HR-TOFMS setup included an Agilent 8890 gas chromatograph with splitless injection at 250 °C, a first-dimension Rxi-5SilMS column (30 m × 0.25 mm × 0.25 µm) and a second-dimension Rxi-17SilMS column (0.6 m × 0.25 mm × 0.25 µm). Helium carrier gas at 1.20 mL/min, oven program from 70 °C to 340 °C, and a dual-stage thermal modulator with variable periods (2 s, 3.2 s, 6 s) were used. Detection employed a LECO Pegasus HRT+4D mass spectrometer with full-scan acquisition at 150 spectra/s over 40–1000 m/z and interchangeable EI, positive chemical ionization (PCI), and ECNI sources.

Methodology

Sample preparation involved homogenizing 10 g of gull liver with sodium sulfate, followed by solvent extraction, ultrasonic treatment, lipid removal by freeze-out, GPC/SEC cleanup, and Florisil chromatography. Non-polar and polar fractions were collected using 10 % dichloromethane/n-hexane and 10 % methanol/dichloromethane, respectively.

Results and Discussion

GC×GC contour plots revealed distinct compound class patterns and minimized coelution, improving detection of persistent organic pollutants (POPs) such as PCBs, BDEs, toxaphenes, phthalates, and DDE. EI spectra provided strong library matches enabling confident identification down to Level 2, while ECNI enhanced selectivity for halogenated species, recovering low-abundance analytes and confirming molecular ions. Tentative identifications were supported by retention index, accurate mass (<1 ppm), reverse similarity scores (>600), and isotopic fidelity.

Benefits and Practical Applications

• Enhanced separation resolves complex mixtures and reveals coeluting trace contaminants
• Structured chromatograms facilitate class-based screening
• High mass accuracy accelerates non-targeted annotation with reduced false positives
• Dual ionization modes provide complementary information for robust identification
• Method applicable to environmental monitoring, ecotoxicology, and regulatory screening

Future Trends and Opportunities

The integration of hybrid data analytics and machine learning for automated feature prioritization will streamline workflows. Expanding high-resolution spectral libraries for ECNI and PCI, along with on-line sample preparation, promises near real-time environmental surveillance. Adaptation to other complex matrices, such as biota and food, will broaden method applications.

Conclusion

Comprehensive GC×GC-HR-TOFMS with multiple ionization modes represents a versatile discovery platform for targeted and non-targeted environmental analysis. The combined separation and accurate mass capabilities deliver high confidence in pollutant identification, advancing our understanding of contaminant burdens in fragile ecosystems.

References

1. Hollender et al Environmental Sciences Europe 2023 35:75
2. Environ Sci Technol 2014 48 2097–2098
3. Exposome 2022 25 osac007