GC soft ionization coupling to LC-MS with SICRIT® (Thermo LTQ Orbitrap XL)

Significance of the Topic

Gas chromatography (GC) and liquid chromatography-mass spectrometry (LC-MS) have long existed as separate analytical domains, each with unique strengths. The introduction of the SICRIT® soft ionization source bridges this gap by enabling direct GC coupling to LC-MS platforms. This innovation delivers high resolution, soft ionization spectra and trace-level sensitivity while leveraging existing LC-MS infrastructure and software.

Study Objectives and Overview

This application note demonstrates a plug-and-play interface between a Thermo Trace GC Ultra and a Thermo LTQ Orbitrap XL mass spectrometer via the SICRIT® GC-SPME module. The goals are to assess:

• Operational compatibility of GC-soft ionization with Orbitrap high-resolution MS.
• Ionization efficiency and fragmentation behavior using a positive tuning mix of trialkylamines.
• Analytical figures of merit: sensitivity, linearity, dynamic range, and repeatability.

Methodology

Samples consisted of a SICRIT® positive tuning mix (tripropylamine, tributylamine, tripentylamine isomers, trihexylamine) in MS-grade n-hexane at concentrations from 1 ppb to 1 ppm. A 1 µL splitless injection was made onto a Restek RXI-5ms capillary column (30 m × 0.25 mm, 0.25 µm). The carrier gas was helium at a constant 2 mL/min flow. The GC oven ramped from 40 °C (0.5 min hold) at 40 °C/min to 280 °C (3 min hold). The transfer line was set to 250 °C. SICRIT® plasma was operated at 1.5 kV and 15 kHz. Full-scan data were acquired on the LTQ Orbitrap XL and processed in Thermo Xcalibur using a 5 ppm mass window.

Used Instrumentation

• Thermo Trace GC Ultra with 5 mm splitless deactivated liner
• Restek RXI-5ms column (30 m × 0.25 mm ID, 0.25 µm)
• Thermo LTQ Orbitrap XL mass spectrometer
• SICRIT® soft ionization source (1.5 kV, 15 kHz)
• MS-grade n-hexane (Sigma Aldrich)

Main Results and Discussion

• Extracted ion chromatograms (100 pg on column) showed increasing peak intensity with alkyl chain length and clear separation of tripentylamine isomers.
• Full-scan spectra were dominated by protonated molecules [M+H]+ with minimal fragmentation, confirming soft ionization.
• Repeatability over seven injections of 1 ppm standards yielded relative standard deviations below 5%.
• Calibration curves from 1 ppb to 1 ppm exhibited excellent linearity (R² > 0.999) for all trialkylamines.

Benefits and Practical Applications

This GC-soft ionization-MS configuration offers:

• Dynamic range exceeding three orders of magnitude.
• Sensitivity down to 1 pg on column.
• Broad soft ionization suitable for targeted quantitation and non-target screening.
• Seamless integration with existing LC-MS data analysis software.

Future Trends and Potential Applications

The combined GC-SICRIT®-Orbitrap workflow is poised to impact fields such as environmental monitoring, food safety, metabolomics, and forensic analysis. Anticipated developments include integration with automated sample prep, expansion to negative ion mode for acidic analytes, and advanced data mining algorithms for comprehensive non-target screening.

Conclusion

The SICRIT® interface enables a straightforward, soft ionization MS coupling of any GC to LC-MS platforms. Demonstrated on a Thermo Trace GC Ultra and LTQ Orbitrap XL, this approach delivers high sensitivity, mass accuracy below 1 ppm, and exceptional dynamic range, opening new avenues for both targeted and untargeted high-resolution analyses.