GC/MS/MS Analysis of PAHs with Hydrogen Carrier Gas

Significance of the Topic

Polycyclic aromatic hydrocarbons (PAHs) are persistent environmental pollutants with toxic and carcinogenic properties. Sensitive, reliable detection in complex matrices such as soil is critical for environmental monitoring and regulatory compliance.

Objectives and Study Overview

This study describes an optimized GC/MS/MS (GC/TQ in MRM mode) method for 27 PAHs using hydrogen carrier gas. By integrating the Agilent HydroInert EI source and mid-column backflush, the goal was to achieve sub-picogram detection limits, excellent linearity, and robust quantitation over 500 challenging soil extract injections.

Methodology and Instrumentation

• Sample Preparation: Topsoil dried, extracted with dichloromethane/acetone, concentrated and spiked at 100 ppb PAHs and 500 ppb internal standards.
• GC Conditions: Agilent 8890 with dual 20 m×0.18 mm DB-EUPAH columns (0.14 µm), pulsed splitless injection (1 µL), constant flow 0.9 mL/min, mid-column backflush (80 psi, 1.5 min).
• MS Conditions: Agilent 7000E TQ, HydroInert source with 9 mm extractor lens, source 325 °C, transfer line 320 °C, dynamic MRM, nitrogen collision gas at 1.5 mL/min, solvent delay 5.5 min.
• Carrier Gas and Source Adaptation: High-purity hydrogen (99.9999%), universal Ultra Inert mid-frit inlet liner, JetClean-style approach to eliminate ISTD drift without added helium in the source.

Results and Discussion

• Calibration and Sensitivity: Linear response (R²≥0.9994) from 0.1 to 1000 pg for 26 analytes (0.25 pg lower limit for one), average MDL 0.09 pg.
• Chromatographic Performance: High peak shape quality, improved resolution versus helium, reduced run time (24 min).
• Matrix Tolerance: MRM mode suppressed soil background; mid-column backflush prevented high-boiling buildup; UI mid-frit liner retained performance over 500 injections.
• Precision and Stability: Routine replacement of septa, liners, and seals every 100–300 injections kept RSDs <5% for most compounds and <12% for all across 500 injections.

Benefits and Practical Applications

This hydrogen-based approach reduces reliance on helium, lowers operating costs, and enhances sensitivity and throughput. Backflush combined with inert inlet liners allows direct analysis of high-matrix environmental samples with minimal downtime, benefiting QC/QA laboratories and environmental monitoring programs.

Future Trends and Applications

Wider adoption of hydrogen carrier gas in GC/MS is expected as gas generators and source technologies advance. Automated self-cleaning ion sources, high-efficiency column materials, and integration of AI for data processing will further improve robustness and throughput in complex sample analysis.

Conclusion

The optimized GC/TQ MRM method using hydrogen carrier gas, the HydroInert source, and mid-column backflush provides exceptional sensitivity, linearity, and long-term stability for trace PAH analysis in soil. This sustainable alternative to helium meets or exceeds performance benchmarks while streamlining maintenance and reducing costs.

References

1. Agilent Technologies. Inert Plus GC/MS with HydroInert Source Technical Overview; publication number 5994-4889EN, 2022.
2. Agilent Technologies. Helium to Hydrogen Carrier Gas Conversion Guide; publication number 5994-2312EN, 2022.
3. Agilent Technologies. Hydrogen Safety Manual for the 8890 GC; part number G3870-90101, 2022.
4. Agilent Technologies. Hydrogen Safety for the 7000E GC/TQ; publication number 5994-5413EN, 2022.
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7. Andrianova AA, Quimby BD. Optimized PAH Analysis Using Triple Quadrupole GC/MS with Hydrogen Carrier. Application note 5994-2192EN, 2020.
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