Soft ionization GC-HRMS of n-Alkanes C8 - C20 (Thermo LTQ Orbitrap XL)

Importance of the Topic

Mineral oil saturated hydrocarbons (MOSH) occur widely in food and environmental samples. Accurate trace analysis of n-alkanes is vital for safety assessment and regulatory compliance. Conventional GC-FID and EI-MS methods suffer from extensive fragmentation and limited isomer specificity, creating a demand for more selective, sensitive analytical strategies.

Objectives and Study Overview

This work presents the first demonstration of GC-SICRIT® soft ionization coupled to high-resolution Orbitrap MS for qualification and quantification of n-alkanes C8–C20. The aim is to achieve gentle ionization with minimal fragmentation, full chromatographic separation, and reliable mass-based identification at trace levels.

Methodology

• Sample: n-alkane standard mix C8–C20 at 40 mg/L in hexane
• Injection: 1 µL splitless
• Carrier gas: helium at 1 mL/min
• Oven program: 40 °C for 2 min, ramp 20 °C/min to 280 °C, hold 6 min

Used Instrumentation

• Gas Chromatograph: Thermo Finnigan Trace GC
• Column: Restek RXI-5ms, 30 m×0.25 mm ID, 0.25 µm
• Soft Ion Source: SICRIT cold-plasma (1.5 kV, 10 kHz)
• Mass Spectrometer: Thermo LTQ Orbitrap XL high-resolution MS

Main Results and Discussion

• All 13 n-alkanes (C8–C20) were baseline-separated and detected.
• Soft ionization yielded dominant oxidized adduct ions [M+O-3H]+ and [M+2O-H]+ with minimal fragmentation.
• High resolution mass spectra delivered mass errors below 1 ppm for characteristic product ions.
• Calibration for C16–C18 showed linear dynamic range over three orders of magnitude, R2>0.999, and low ppb-level limits of detection.

Benefits and Practical Applications

GC-SICRIT-HRMS combines soft ionization with high-resolution detection to enhance sensitivity and specificity for nonpolar hydrocarbons. This approach supports improved MOSH profiling in food safety testing, environmental monitoring, and industrial quality control.

Future Trends and Potential Applications

• Extension to broader hydrocarbon classes and complex environmental matrices
• Integration with diverse MS platforms for regulatory workflows
• Development of standardized soft-ionization protocols for routine QC
• Automation and high-throughput screening in environmental and food laboratories

Conclusion

The presented GC-SICRIT®-HRMS method offers a fast, robust, and sensitive solution for trace analysis of n-alkanes C8–C20. Soft plasma ionization simplifies spectra, enhances identification confidence, and delivers reliable quantification, marking a significant advance in MOSH analytics.

References

1. Alam MS et al Anal Chem 2016 88 8 4211–4220
2. Mirabelli MF et al Analyst 2017 142 1909–1915
3. Nunome Y et al Talanta 2019 204 310–319