Novel Analysis Method of Various Environmental Samples Using GC×GC-HRMS with Encoded Frequent Pulsing™ (EFP™)

Importance of the Topic

Environmental monitoring requires highly sensitive and selective analytical methods to detect trace contaminants in complex matrices. Comprehensive two-dimensional gas chromatography coupled with high-resolution time-of-flight mass spectrometry (GC×GC-HRMS) addresses challenges in separating and identifying diverse compounds at sub-picogram levels. Encoded Frequent Pulsing™ (EFP™) further enhances sensitivity by multiplexing without compromising spectral fidelity or chromatographic resolution.

Objectives and Study Overview

This work demonstrates the performance of a GC×GC-HRMS platform equipped with EFP technology for the analysis of environmental standards and pesticide residues. Key goals include:

• Establishing baseline sensitivity with and without EFP
• Evaluating detection limits in a complex mixture of 317 environmental analytes
• Assessing real-world performance in spiked matrix samples (pesticide residues in eggplant)

Instrumentation

• Pegasus® GC-HRT: high-resolution multi-reflecting TOFMS with 20 m flight path, resolving power >50 000, sub-ppm mass accuracy, acquisition up to 200 spectra/s
• Comprehensive two-dimensional GC module with thermal modulation

Methodology

The study used EFP, a novel multiplexing approach employing unequal pulse intervals and real-time decoding to boost duty cycle and sensitivity. Method steps included:

1. Injection of perfluorokerosene (OFN) standards at 1 pg/µL without EFP and at 0.10 and 0.05 pg/µL with EFP to calculate instrument detection limits (IDLs)
2. Analysis of a 317-compound environmental standard mix (100 pg/µL) by 1D GC-HRMS at 8 spectra/s and by GC×GC-HRMS at 200 spectra/s
3. Pesticide residue study: eggplant extracts spiked at 5 pg/µL and analyzed under identical GC×GC conditions

Main Results and Discussion

Key findings include:

• IDL improvement from 0.12 pg/µL (no EFP) to 0.02 pg/µL (with EFP)
• Retention of GC×GC peak resolution and separation performance at 200 spectra/s
• Clear contour plots and zoomed-in chromatograms showing detection of trace analytes in complex mixtures
• Successful identification of multiple pesticides at 5 pg/µL in an eggplant matrix without loss of sensitivity

Benefits and Practical Applications

The integration of EFP with GC×GC-HRMS offers:

• Enhanced sensitivity for sub-picogram contaminant detection
• Robust separation of coeluting compounds in complex samples
• High-throughput data acquisition supporting environmental monitoring, food safety, and forensic analysis

Future Trends and Applications

Potential developments include combining EFP-enabled GC×GC-HRMS with automated sample preparation, expanding to other challenging matrices (biological fluids, soils), and deploying portable or field-ready systems. Further optimization of pulse coding schemes may yield additional gains in sensitivity and throughput.

Conclusion

Encoded Frequent Pulsing™ on a high-resolution, multi-reflecting TOFMS platform substantially improves detection limits while preserving mass accuracy and chromatographic resolution. This approach holds promise for advanced environmental and pesticide analyses requiring trace-level quantitation in complex matrices.