Performance of Method 8270 Using Hydrogen Carrier Gas

Significance of the Topic

Laboratories analyzing semivolatile organic compounds by EPA Method 8270 face challenges from rising helium costs and supply constraints. Switching to hydrogen carrier gas can reduce operational expenses and ensure continuous on-demand gas generation. However, hydrogen’s reactivity and safety concerns require a robust GC/MS system designed to maintain analytical performance and prevent compound degradation.

Objectives and Overview of the Study

This work evaluates the compatibility of hydrogen as a carrier gas for EPA Method 8270 using the Scion GC/MS platform. Key goals include demonstrating tune stability, calibration accuracy, peak shape integrity, spectral library matching, and robustness in complex matrices such as contaminated sludge extracts.

Used Instrumentation

• Gas Chromatograph: Scion 436 with SSL pulsed-split injector
• Mass Spectrometer: Scion Select SQ axial ion source with Helium-free package
• Carrier Gas Generator: Peak Precision 500 Trace H₂ Generator
• Column: SGE BP-5 MS, 20 m × 0.18 mm × 0.18 µm

Methodology

Chromatographic parameters were optimized for hydrogen flow at 1.0 mL/min with a pulsed split injection (0.5 µL, 40 psi pulse for 0.3 min) to minimize inlet residence time. Oven temperature programming ranged from 45 °C to 310 °C over a 28 min run. Mass spectrometer settings included a 45–500 Da scan range, 250 ms dwell time, ion source at 330 °C (raised to 350 °C during initial clean-up), and transfer line at 300 °C. Calibration standards (1–200 ppm) and internal/surrogate standards at 40 ppm were prepared in dichloromethane.

Main Results and Discussion

• Auto-tune and DFTPP tuning were achieved without modification using hydrogen, yielding stable tune files and low spectral distortion.
• System performance checks (SPCC) and continuing calibration checks (CCC) met EPA criteria with relative response factors (RRF) above 0.05 and %RSDs below 15% (average RSD ~8.5%).
• Peak shape for challenging analytes (e.g., Pentachlorophenol, Benzo(b,k)fluoranthene) demonstrated Gaussian factors within method limits.
• Calibration curves showed correlation coefficients (r²) ≥0.9968, with example r²=0.9998 (Hexachlorocyclopentadiene, %RSD 3.9%).
• Library matching against NIST 11 provided high match scores (>900) for key compounds, confirming spectral integrity under hydrogen.
• Fifty repeated injections of a sludge extract with CCC every ten runs confirmed robust performance and surrogate recovery within ±15% over time.

Benefits and Practical Applications

• Eliminates reliance on helium cylinders and associated supply disruptions.
• On-site hydrogen generation enhances safety and lowers long-term operating costs.
• Scion’s inert flow path and axial ion source prevent compound degradation and unwanted protonation.
• Suits a broad range of environmental matrices, from clean water to contaminated sludge.

Future Trends and Applications

• Integration of hydrogen carrier gas into additional EPA and ISO methods to reduce consumable costs.
• Development of advanced inlet liners and coatings to further minimize analyte reactivity.
• Adoption of real-time hydrogen monitoring and leak detection for enhanced laboratory safety.
• Advances in software deconvolution and AI-driven library matching to support reactive carrier gases.

Conclusion

The Scion 436/Select SQ GC/MS system with a Helium-free package successfully meets all EPA Method 8270 requirements using hydrogen carrier gas. Performance metrics—tuning stability, calibration accuracy, peak shape, spectral quality, and matrix robustness—confirm hydrogen as a viable, cost-effective alternative to helium for routine semivolatile analyses.

Reference

• USEPA Method 8270D, Revision 4, February 2017