Evaluation of the NIST Library Matching Quality of Mass Spectra Generated by the GC-HR-TOFMS with Multi-Mode Ionization Source

Importance of the Topic

Non-targeted GC-MS identification relies on matching electron ionization spectra against established libraries such as NIST for accurate compound recognition. Advances in high-resolution mass spectrometry instruments can alter fragmentation patterns, potentially affecting automated library matching performance. Thorough evaluation of new ion sources and analyzers against standardized libraries is essential to maintain confidence in analytical results.

Objectives and Study Overview

This work evaluates the quality of EI spectra generated by LECO’s novel Multi-mode Source paired with a multi-reflecting high-resolution time-of-flight mass spectrometer (HR-TOFMS). Data were acquired for 207 analytes across seven certified standards and two complex matrices spiked with multiresidue pesticide mixtures. All spectra were matched against the NIST23 library to assess performance across compound classes and sample types.

Methodology and Instrumentation

A comprehensive GC×GC setup employed Rxi-5 ms (30 m × 0.25 mm × 0.25 µm) and Rxi-17Sil MS (2 m × 0.25 mm × 0.25 µm) columns with a temperature program from 40 °C to 320 °C. The Pegasus GC-HRT+ 4D HR-TOFMS operated at a resolving power of 25 000 and acquired data at 200 spectra/s over m/z 15–1500. Electron ionization at 250 °C was used. Automated peak finding, deconvolution, and library searching were performed with LECO ChromaTOF software against NIST23.

Used Instrumentation

• GC×GC system with dual columns (Rxi-5 ms and Rxi-17Sil MS)
• Pegasus GC-HRT+ 4D HR-TOFMS (R=25 000; mass range m/z 15–1500)
• LECO Multi-mode Electron Ionization Source (250 °C)
• LECO ChromaTOF software for deconvolution and spectral matching

Main Results and Discussion

An average library match score of 935 (±24.2) was obtained across all standards. Individual mixture scores ranged from 920 for alkanes to 941 for certain pesticide sets. Functional group stratification showed robust scores (>928) for all moieties, with ketones (951) and nitriles (948) performing best. Complex sample matrices caused minimal decreases in match quality (−3.75% for tea, −1.44% for dietary supplement), demonstrating the method’s resilience to interference.

Benefits and Practical Applications of the Method

• High-confidence compound identification in non-targeted GC-MS and GC×GC-MS analyses
• Consistent library matching across diverse chemical classes and matrices
• Improved sensitivity and resolution without compromising spectral fidelity
• Streamlined automated data processing for rapid results

Future Trends and Applications

• Machine learning–enhanced spectral matching for greater specificity
• Expansion of high-resolution spectral libraries tailored to novel ion sources
• Real-time non-targeted screening workflows for environmental and food safety testing
• Portable GC-HR-TOFMS systems for on-site analysis in field settings

Conclusion

The LECO multi-mode electron ionization source combined with a high-resolution TOF analyzer generates spectra that align closely with the NIST library. The approach delivers high-quality match scores across a wide range of analytes and matrices, reinforcing its value for confident non-targeted GC-MS and GC×GC-MS applications.