From Helium to Hydrogen: GC-MS Case Study on SVOC’s in water

Importance of the Topic

Substituting helium with hydrogen as the carrier gas in gas chromatography–mass spectrometry (GC-MS) addresses rising helium costs and supply constraints. Hydrogen offers superior diffusion and lower viscosity, leading to faster separations, higher throughput and reduced operating expenses in environmental laboratories analyzing semi-volatile organic compounds (SVOCs) in water.

Goals and Study Overview

• Compare chromatographic performance using hydrogen versus helium for EPA methods 524, 525 and 8270.
• Assess instrument tuning, spectral integrity and method detection limits (MDLs) with hydrogen.
• Evaluate safety, gas purity and practical implementation of hydrogen carrier systems.

Methodology and Instrumentation

The study began with a theoretical comparison of carrier gas properties (molecular mass, density, diffusion coefficient and viscosity) and van-Deemter profiles, demonstrating hydrogen’s higher optimum linear velocity. Experimental work used:

• Thermo Scientific ISQ single-quadrupole GC-MS, TRACE 1300 GC and TSQ 8000 GC-MS/MS.
• Hydrogen delivery via UHP cylinders (Grade 5.0/6.0) or on-site generators, equipped with triple-stage filters and hydrogen sensors in the GC oven.
• Columns: TG-5 SilMS (20 m × 0.18 mm × 0.36 µm) and TG VMS (20 m × 0.18 mm × 1 µm).
• Injection: split/splitless at 300 °C, purge & trap for volatile methods (EPA 524), direct liquid injection for SVOC methods (EPA 525, 8270).
• Tuning standards: DFTPP for electron ionization (EI) and 4-bromofluorobenzene (BFB) for chemical ionization (CI).

Main Results and Discussion

Van-Deemter experiments confirmed hydrogen’s flatter curve on the right half, allowing higher linear velocities (~40 cm/s) without loss of resolution. PCB and PNA mixtures run at increased oven heating rates (30–50 °C/min) showed equivalent peak separation with hydrogen. Flow optimization indicated use of narrower bore columns at 1 mL/min hydrogen for balance of efficiency and backpressure.
Mass spectra of tuning compounds (DFTPP, BFB) under hydrogen matched helium reference spectra. Ion ratio stability over multiple runs met EPA criteria. Bake-out at 350 °C with 4 mL/min H2 minimized hydrocarbon background. Purge & trap analysis (EPA 524) achieved average MDLs of 0.074 ppb (versus 0.048 ppb with helium) and passed spectral library match requirements. Direct injection methods (EPA 525, 8270) maintained linearity over the calibrated range, accuracy within ±50%, and fast runtimes below 15 minutes. Low-level PNA quantification demonstrated RSDs below 10% for most analytes and reliable spectral purity.

Benefits and Practical Applications

• Reduced carrier gas cost and dependency on helium supply.
• Shorter analysis times and improved sample throughput.
• Compliance with EPA method quality control requirements.
• Compatibility with existing GC-MS systems via hydrogen kits and turbo pump upgrades.

Future Trends and Potential Applications

The adoption of hydrogen will expand beyond environmental testing into food safety, petrochemical and clinical laboratories. Advances in on-site hydrogen generators, integrated safety sensors and data-driven method optimization will further streamline workflows. Integration with AI-driven tuning and automated QC monitoring is expected to enhance reproducibility and method development.

Conclusion

Hydrogen is a viable carrier gas alternative in GC-MS for SVOC analysis, offering cost savings, faster separations and maintained analytical performance. With proper safety measures, gas purity control and system tuning, laboratories can transition from helium to hydrogen without compromising method integrity.

Used Instrumentation

• Thermo Scientific ISQ Single Quadrupole GC-MS, TRACE 1300 GC, TSQ 8000 GC-MS/MS.
• Hydrogen generator or UHP H₂ cylinders (Grade 5.0/6.0) with triple-stage filtration.
• Columns: TG-5 SilMS 20 m × 0.18 mm × 0.36 µm; TG VMS 20 m × 0.18 mm × 1 µm.
• Purge & Trap module VOCARB for EPA Method 524.2.
• Tuning kits: DFTPP (EI), BFB (CI).

Reference

O. Fryazinov, A. Pasko, V. Adzhiev, "Crystal Lattice Density Analogy Only," Computer-Aided Design, 2011, 43(3):265–277.