Analysis of PAHs Using Hydrogen Carrier Gas and the Hydrogen-Optimized Source with GC/MS and GC/MS/MS in Challenging Soil Matrix

Importance of the Topic

Polycyclic aromatic hydrocarbons (PAHs) are widespread environmental pollutants with significant health and ecological risks due to their persistence and potential carcinogenicity. Accurate, sensitive, and robust analytical methods are essential for monitoring PAH contamination in challenging matrices such as soil. The transition from helium to hydrogen carrier gas addresses rising helium costs and shortages while maintaining or improving analytical performance.

Study Objectives and Overview

This work evaluates a triple quadrupole GC/MS/MS method using hydrogen as the carrier gas, an Agilent HydroInert source, and mid-column backflush to analyze 27 PAH compounds in a complex soil extract. Key goals include achieving low detection limits, excellent calibration linearity, stable internal standard responses, and sustained quantitation performance over 500 injections of a demanding soil matrix.

Experimental Methodology

Soil samples were dried, extracted with dichloromethane/acetone, concentrated, and spiked with 27 PAHs (100 ppb) and five isotopically labeled standards (500 ppb). Twelve calibration levels from 0.1 to 1000 pg/µL were prepared in isooctane. Method robustness was assessed by performing 500 consecutive injections of spiked soil extract, replacing inlet liner and septa every 100 injections and the gold seal every 300 injections.

Used Instrumentation

• Agilent 8890 GC with Fast Oven, split/splitless inlet, pulsed injection
• Agilent 7000E triple quadrupole MS with HydroInert source
• Agilent J&W DB-EUPAH column (20 m × 0.18 mm, 0.14 µm film)
• Pneumatic Switching Device for mid-column backflush

Main Results and Discussion

The method delivered sharp chromatographic peaks and mid-picogram sensitivity. Twenty-six of 27 PAHs exhibited linear calibration (R2 > 0.9994) over four orders of magnitude (0.1–1000 pg); one compound calibrated from 0.25 pg. Average method detection limit was 0.09 pg. The HydroInert source and 9 mm extractor lens eliminated the internal standard signal drift commonly seen with hydrogen or helium sources. Over the 500-injection sequence, 23 analytes maintained <5% RSD in calculated concentration for each block of 100 injections; overall RSD remained <12% despite heavy soil matrix. Liner saturation effects on four late-eluting PAHs were reversed by routine inlet maintenance, demonstrating effective matrix trapping by the ultra-inert mid-frit liner.

Benefits and Practical Applications

• Comparable or improved sensitivity and linearity versus helium methods
• Faster analysis with enhanced chromatographic resolution
• Stable internal standard response across a wide calibration range
• High throughput robustness for routine environmental monitoring
• Cost savings and sustainability from hydrogen carrier gas

Future Trends and Opportunities

Advances in hydrogen-optimized ion source design and mid-column backflush techniques will further improve sensitivity and matrix tolerance. Integration with automated sample preparation and high-throughput workflows can expand applications to other persistent organic pollutants. Emerging data analysis tools and machine learning approaches offer prospects for real-time quality control and predictive maintenance of GC/MS systems.

Conclusion

The hydrogen-based GC/MS/MS method with an Agilent HydroInert source and backflush delivers excellent sensitivity, linearity, and robustness for PAH analysis in complex soil matrices. It provides a sustainable alternative to helium without sacrificing analytical performance, supporting reliable environmental monitoring and regulatory compliance.

References

Haddad S.P., Quimby B.D., Andrianova A.A. GC/MS/MS Analysis of PAHs with Hydrogen Carrier Gas Using the Novel Agilent HydroInert Source in a Challenging Soil Matrix, Agilent Technologies Application Note 5994-5776EN, 2023
© Agilent Technologies, Inc. 2023