A Novel Robust Direct Extraction EI Source for GC-TOFMS and GCxGC-TOFMS

Importance of the Topic

A robust and high-sensitivity ion source is critical for modern gas chromatography–time-of-flight mass spectrometry (GC-TOFMS) and comprehensive two-dimensional GC-TOFMS (GCxGC-TOFMS). Enhanced detection limits enable trace-level analysis in environmental monitoring, food safety, pharmaceuticals and petrochemicals. A gridless direct extraction electron ionization (EI) source promises improved sensitivity, mass accuracy and operational robustness under challenging sample matrices.

Objectives and Study Overview

This study presents the development and evaluation of a novel gridless direct extraction EI source integrated into a Pegasus BT 4D prototype system. Key aims include:

• Assessing instrument detection limits (IDL) for octafluoronaphthalene (OFN) under GC-TOFMS and GCxGC-TOFMS modes
• Evaluating molecular ion generation efficiency and spectral quality
• Demonstrating long-term robustness under repeated injections of complex matrices

Methodology and Instrumentation

Experiments were performed on a prototype Pegasus BT 4D GCxGC-TOFMS platform equipped with the novel gridless EI source. Operating parameters included an extraction frequency of 30–32 kHz, ion source and transfer line temperatures up to 320 °C, and mass range m/z 35–635. GC separations utilized RXI-5MS and RXI-17SILMS columns in both one- and two-dimensional configurations with tailored temperature programs. Samples comprised OFN standards and multi-analyte QuEChERS extracts of spinach and black tea, injected via split and splitless modes.

Main Results and Discussion

Detection limits for OFN were determined by eight replicate injections and calculated with a t-statistic approach at 99 % confidence. Key outcomes:

• GC-TOFMS IDL: 6.5 fg on column (20 fg injections, S/N ~20.6, RSD ~10.8 %)
• GCxGC-TOFMS IDL: 2.1 fg on column (10 fg injections, S/N ~36.5, RSD ~7.0 %)
• Spiked spinach QuEChERS extracts yielded IDLs in the 3.6–21.6 fg range across eight pesticides and polyaromatic hydrocarbons

High-quality molecular ion formation was demonstrated for a low-mass compound (dodecanoic acid methyl ester) with excellent similarity to NIST library spectra. Robustness testing with 1 000 injections of black tea extract showed consistent OFN peak areas and RSD values below 17 % across a concentration range of 5 fg to 1 pg.

Benefits and Practical Applications

The gridless source offers near-100 % duty cycle and reduced contamination risk due to its open-style design. Key advantages include:

• Sub-10 fg detection limits for routine trace analysis
• Reliable molecular ion generation for structural confirmation
• Enhanced uptime and minimal signal degradation in dirty matrices

These features support high-throughput workflows in environmental testing, food safety screening and quality control laboratories.

Future Trends and Potential Applications

Gridless EI technology may be further refined through advanced materials and optimized electrode geometries. Integration with real-time data processing and machine-learning-based deconvolution will expand its utility. Potential applications include on-site environmental monitoring, metabolomics profiling and forensic screening.

Conclusion

The novel gridless direct extraction EI source on the Pegasus BT 4D platform delivers exceptional sensitivity, spectral integrity and operational robustness. Sub-5 fg detection limits in GCxGC-TOFMS and stable performance after extensive use in complex matrices demonstrate its suitability for demanding analytical tasks.

Reference

Soyk M, Artaev V, Judkins T. A Novel Robust Direct Extraction EI Source for GC-TOFMS and GCxGC-TOFMS. LECO Corporation, St. Joseph MI 2023.