High Mass Resolution is Essential for Confident Compound Detection

Significance of the Topic

Analytical laboratories face growing pressure to deliver rapid, accurate results for an ever-expanding range of compounds in complex matrices. High-resolution, accurate-mass (HR/AM) full-scan gas chromatography–Orbitrap mass spectrometry offers comprehensive screening, retrospective data mining, and confident compound identification while preserving selectivity and sensitivity.

Objectives and Overview of the Study

This technical note presents the Thermo Scientific Q Exactive GC hybrid quadrupole-Orbitrap system, evaluating its performance for targeted pesticide screening and unknown compound discovery in food extracts. Key aims include demonstrating the impact of mass resolution on selectivity, assessing sensitivity retention at high resolution, and illustrating sub-ppm mass accuracy for elemental composition elucidation.

Instrumentation Used

• Thermo Scientific Q Exactive GC hybrid quadrupole-Orbitrap mass spectrometer
• Gas chromatograph with electron impact ionisation source
• Full-scan acquisition over 50–1000 m/z at 15 000, 30 000, 60 000, and 120 000 FWHM (m/z 200)

Methodology

Leek and carrot samples were extracted using QuEChERS (acetonitrile). Full-scan spectra were acquired at multiple resolving powers. Target analytes were quantified by extracting diagnostic ions within narrow mass windows (<5 ppm). Retrospective data mining employed elemental formula calculators with tolerances ranging from 0.5 to 10 ppm.

Main Results and Discussion

At 15 000 and 30 000 resolution, chlorpropham (m/z 127.01833) co-eluted with a matrix ion, producing a mass error up to 18.4 ppm and a false negative under typical screening criteria (<5 ppm). Resolutions ≥60 000 achieved baseline separation, delivering sub-ppm mass accuracy. Sensitivity for pesticides at 10 ng/g remained consistent across 15 000, 60 000, and 120 000 modes, maintaining peak areas and at least 12 scans per peak. Sub-1 ppm accuracy reduced elemental formula candidates from 60 at 10 ppm to 2 at 0.5 ppm, enabling rapid identification of unknowns such as diazinon.

Benefits and Practical Applications of the Method

• Full-scan screening with retrospective analysis capability
• High confidence in targeted assays via accurate mass and high resolution
• Uncompromised sensitivity at elevated resolving powers for quantification
• Efficient discovery and identification of unknown compounds through precise elemental composition

Future Trends and Opportunities

Advances may include integration with expanded spectral libraries, AI-driven data mining, and enhanced non-target screening workflows. Broader applications are anticipated in environmental monitoring, food safety, and pharmaceutical analysis.

Conclusion

The Q Exactive GC Orbitrap system delivers routine high resolving power (≥60 000 FWHM), consistent sub-ppm mass accuracy, and stable sensitivity, offering a versatile solution for comprehensive screening, quantitation, and structural elucidation in complex matrices.

References

• Thermo Scientific Application Note 617: Quantitative and Qualitative Confirmation of Pesticides in Beet Extract Using a Hybrid Quadrupole-Orbitrap Mass Spectrometer