Miniature Combustion Reactors to Increase Sensitivity, and to Facilitate Comprehensive Two-dimensional Gas Chromatography (GC×GC) for Compound-specific Isotope Analysis (CSIA)

• Applicant: Professor Dr. Martin Elsner
• Subject Area: Chemical and Thermal Process Engineering ; Analytical Chemistry
• Term: since 2025
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 558998366

Online combustion reactors between gas chromatography and isotope ratio mass spectrometry (GC-C-IRMS) have been the enabling innovation for compound-specific isotope analysis (CSIA). CSIA has triggered breakthroughs in multiple disciplines including the detection of environmental pollutant degradation, or of doping in sports. Yet, many CSIA applications are still out of reach for want of better peak resolution and higher sensitivity. Comprehensive two-dimensional gas chromatography (GC×GC) with narrow separation columns could deliver a breakthrough, but hinges on the development of robust miniaturized combustion tubes. The step change from inner diameters of 0.05–0.1 mm to current commercial combustion tubes (0.8 mm) generates peak broadening that would give away the enhanced peak resolution of GC×GC. Tubes are warranted with sufficient oxidation capacity and catalytic surface area to accomplish complete analyte conversion to CO2, while being narrow enough to preserve peak shapes within the continuous flow carrier stream. Self-made reactors reported in the past were insufficiently robust and too short-lived for routine applications. To pioneer a drastic reduction of reactor tube size while maintaining sufficient oxidation capacity and ensuring robustness and longevity, we aim to explore the promise of two designs: (i) wall-coated capillary (WCC) reactors to eliminate complications related to wire insertion inside reactor tubes. This approach has the benefit of simplicity, while allowing for the fabrication of capillary reactors with a narrow bore size of 0.1 mm, which is not achievable with hand-loading of metal wires. In addition, the design allows constructing bimetallic reactors with optimized compositions for complete oxidation. (ii) A solid-electrolyte reactor, in which the combustion occurs via electrochemical oxidation. This design eliminates the need of adding a chemical oxidant thereby facilitating reactor design and efficiency. Development of reactor tubes will be guided by (a) Scanning Electron Microscopy (SEM) with energy-dispersive X-ray Fluorescence Spectroscopy (EDX) to optimize the coating, (b) molecular MS to detect and avoid oxidation-by-products and (c) characterization by IRMS to ensure the isotopic integrity of results. With this innovative approach we want to push a long-expected breakthrough and shift the boundaries of isotope analysis for advances in multiple disciplines such as paleoclimatology, biogeochemistry, plant sciences, food science, forensics, pollutant dynamics, doping and many more.

• DFG Programme: Research Grants
• Co-Investigator: Professor Dr. Ralf Zimmermann