Hydrogen Carrier Gas Method Translation in Comprehensive Two- Dimensional Gas Chromatography for Sustainable Nontargeted Analysis

Importance of the Topic

The availability and choice of carrier gas in gas chromatography (GC) and comprehensive two-dimensional gas chromatography (GC×GC) directly influence chromatographic efficiency, analysis time, operating cost, and environmental footprint. Historically, helium has been the preferred carrier gas due to chemical inertness and compatibility with mass spectrometry, but supply limitations, rising cost, and fossil-derived sourcing motivate evaluation of hydrogen as a sustainable alternative. This study addresses the practical translation of cryogenically modulated GC×GC-TOFMS methods from helium to hydrogen, quantifies effects on chromatographic performance and throughput, and assesses sustainability using green-chemistry metrics.

Objectives and Study Overview

This technical note aimed to (1) adapt 1D GC helium-to-hydrogen translation tools for cryogenic GC×GC-TOFMS, (2) evaluate three hydrogen-translation strategies (translate, efficiency, speed) using standard mixtures, (3) determine appropriate modulation-period adjustments for the second dimension, and (4) validate the recommended workflow with authentic fingermark residue samples as a nontargeted forensic application.

Methodology

- Standards and samples: a 52-component indoor-air VOC standard, a Grob test mix, a C7–C30 n-alkane ladder, seven fingermark-related lipid standards, and authentic fingermark residues from volunteers.
- Translation tool: Pro EZGC Method Translator (Restek) was used to convert established 1D helium methods into three hydrogen variants: translate (match column efficiency by combined flow and temperature adjustments), efficiency (flow optimized for maximal plate count), and speed (flow and optimal heating rate optimized for fastest analysis).
- Instrumentation and configuration: GC×GC-TOFMS with dual-stage cryogenic quad-jet modulation (LECO Pegasus BT 4D), Rxi-5 ms primary column (30 m × 0.25 mm × 0.25 μm) and Rxi-17Sil MS secondary column (0.90 m × 0.25 mm × 0.25 μm), liquid injection (1 μL, split 20:1), high acquisition rates (200 spectra/s), and electron ionization (70 eV). Hydrogen was generated on-site (VICI NM Plus 600, 99.9996%) with stainless steel transfer tubing to reduce safety risk.
- Data processing: ChromaTOF for peak metrics and NIST MS library searches; peak capacities calculated with Simply GC×GC software. Greenness evaluated by BAGI, MoGAPI, and AGREE metrics.

Used Instrumentation

• GC×GC-TOFMS (LECO Pegasus BT 4D) with cryogenic dual-stage quad-jet modulator.
• Primary column: 30 m × 0.25 mm ID × 0.25 μm Rxi-5 ms.
• Secondary column: 0.90 m × 0.25 mm ID × 0.25 μm Rxi-17Sil MS.
• Hydrogen generator: NM Plus 600 (VICI DBS), hydrogen purity ~99.9996%.
• Data system: ChromaTOF v5.58; NIST MS Library for identification.

Main Results and Discussion

- Run-time and throughput: Hydrogen methods reduced run time substantially versus helium. Depending on the hydrogen option, run time reductions were ~1.66× (translate), ~1.96× (efficiency), and ~2.36× (speed); the translate option achieved ~60% reduction in run time in practical configurations reported in this study, nearly doubling daily sample throughput (e.g., ~52 vs ~31 samples/day).

- Chromatographic performance: The translate option (combined flow and temperature adjustments to match column efficiency) delivered the best balance of peak shape, tailing factors, S/N, and resolution compared to helium and the other hydrogen options. Speed-optimized hydrogen gave shortest analyses but worse peak shape and increased tailing for some analytes. Efficiency-optimized hydrogen improved peak shapes relative to the speed option but did not outperform the translate option for broad nontargeted workflows.

- Second-dimension (2D) behavior and modulation: Hydrogen produced markedly faster elution in the second dimension. Across standards and fingermark samples, 2D retention times shortened by roughly a factor of 2, leading to a practical recommendation to reduce the modulation period by ~50% when switching from helium to hydrogen in cryogenically modulated systems (e.g., 2.0 s → 1.0 s). This reduction preserved the number of modulations per first-dimension peak and avoided wraparound when applied appropriately.

- Mass spectral identification and reactivity: All detected compounds in standards and fingermark samples were identifiable under both carrier gases with no systematic loss of library match. Although hydrogen can in principle promote reductive reactions or slight changes in EI fragmentation for certain sensitive chemistries, no identification impediments were observed in this dataset. Monitoring for analyte reactivity is nevertheless recommended during method transfer, especially for oxygenated or unsaturated species.

- Greenness assessment: Using BAGI, MoGAPI, and AGREE metrics, hydrogen methods scored equal or better overall. BAGI and AGREE favored hydrogen due to increased throughput and the option for in-house electrolysis-based hydrogen production (improved renewability scores). MoGAPI scores were similar between gases. Hydrogen’s flammability reduced safety-scoring elements in some metrics; mitigating measures (in-house generation, minimal storage, stainless steel tubing, appropriate ventilation) are advised.

Benefits and Practical Applications

• Substantial reduction in analysis time and energy consumption per sample, increasing laboratory throughput for high-volume applications (forensics, food control, environmental monitoring).
• On-site hydrogen generation reduces logistics (cylinder deliveries), fossil-derived supply dependence, and may improve sustainability profiles when electricity for electrolysis is from low-carbon sources.
• The translate workflow uses existing 1D translation tools with specific adjustments for GC×GC (notably halving modulation period), enabling practical adoption with minimal equipment changes.
• Maintains comparable chromatographic separation power (peak capacity) and identification capability for diverse VOC and lipid analytes when the translate option is chosen.

Limitations and Risks

• Hydrogen is flammable—safety protocols, hydrogen generators (to minimize cylinder storage), stainless steel gas lines, and appropriate ventilation are essential.
• Possible analyte reactivity (reduction/hydrogenation) should be evaluated for analyte classes not covered here; certain reactive functionalities may require validation or alternative approaches (e.g., column/source deactivation, derivatization).
• This study focused on cryogenic modulation; flow-modulated GC×GC may exhibit different translation behavior and warrants dedicated investigation.

Workflow Recommendations for Translating Helium GC×GC Methods to Hydrogen

1. Use a 1D translator (e.g., Pro EZGC) to generate candidate hydrogen methods (translate, efficiency, speed) from the validated helium method.
2. Prefer the translate option to balance peak shape and reproducibility unless throughput constraints demand speed optimization.
3. Increase carrier flow per translator output and reduce primary oven heating rates accordingly; adjust acquisition delay to ensure early-eluting peaks are captured.
4. Reduce cryogenic modulation period approximately 50% to accommodate faster second-dimension elution; verify number of modulations/peak and avoid wraparound.
5. Validate with representative standards and authentic matrix samples, checking peak capacity, resolution of diagnostic peak pairs, S/N, tailing, and spectral matches.
6. Assess potential analyte reactivity; consider source/column deactivation or derivatization if needed.
7. Incorporate safety and sustainability considerations (on-site generation, line materials, ventilation) into implementation plans.

Future Trends and Potential Applications

Hydrogen is likely to be increasingly adopted for routine GC and GC×GC analyses as helium supply constraints persist. Anticipated developments include optimized translation software tailored to multidimensional separations (including flow-modulation), dedicated MS spectral libraries or correction factors for hydrogen-carrier datasets, expanded studies on analyte reactivity across compound classes, and improved instrument designs for safe, integrated hydrogen generation and delivery. Greater use of renewable-electricity-driven electrolysis will further strengthen hydrogen’s sustainability advantages.

Conclusions

This work demonstrates a practical, validated pathway to translate cryogenically modulated GC×GC-TOFMS methods from helium to hydrogen using existing 1D translation tools combined with GC×GC-specific adjustments. The translate option yields the best compromise between chromatographic fidelity and speed; modulation periods can be halved when keeping column geometry constant. Hydrogen reduces run time and per-sample energy use while maintaining identification performance for the examined standards and fingermark matrices, offering a viable route to more sustainable high-throughput GC×GC analyses when appropriate safety and reactivity assessments are performed.

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