Wasson Chromatography Corner 9

Importance of the Topic

Monitoring trace sulfur compounds in human breath and profiling paraffins, olefins and carbon oxides in gas-to-liquid (GTL) processes are critical for both medical diagnostics and industrial process control. Inhaled analysis of volatile sulfur compounds (VSCs) supports research into halitosis and metabolic disorders, while detailed GTL gas characterization ensures reaction completeness and prevents catalyst poisoning in downstream refinery operations.

Objectives and Study Overview

The newsletter presents two case studies:

• Quantitative analysis of trace VSCs in human breath using a dual-flame photometric detector (FPD/FPD).
• Comprehensive profiling of paraffins, olefins and trace carbon oxides in GTL gas streams with a multi-detector gas chromatograph (FID/FID/TCD/TCD).

Applied Methodology and Instrumentation

Breath analysis:

• A custom vacuum sampling manifold collects 10 mL of expired breath in under three seconds.
• An Agilent gas chromatograph modified with dual FPDs excites sulfur species in a hydrogen flame; selective optical filters and a photomultiplier tube measure light emission at specific wavelengths.
• Lower detection limits (LDL) of 0.1 ppm achieved for hydrogen sulfide, carbonyl sulfide, methyl mercaptan and dimethyl sulfide.

GTL gas profiling:

• An Agilent 7890A GC configured with two flame ionization detectors (FID A and FID B) and two thermal conductivity detectors (TCD A and TCD B).
• FID A resolves C1–C5 paraffins and olefins (LDL 10 ppm); FID B quantifies C6–C9 paraffins/alpha-olefins (LDL 10 ppm) and, via a methanizer, carbon monoxide and dioxide (LDL 0.1 ppm).
• TCD A detects CO₂, C₂–C₃ hydrocarbons, acetylene, argon/oxygen and nitrogen (LDL 400 ppm); TCD B monitors hydrogen (LDL 100 ppm); signals are summed electronically for unified output.

Main Results and Discussion

The dual-FPD approach enabled clear chromatographic separation and quantification of key VSCs associated with halitosis. In the GTL study, the multi-detector GC overcame the challenge of analyzing numerous components in a single run, delivering reliable ppm-level data on paraffins, olefins and catalyst-poisoning oxides. Custom sampling and backflush techniques prevented carryover and maintained tight peak shapes.

Contributions and Practical Applications

This work supports clinical and research laboratories in noninvasive diagnosis of oral and metabolic health. In industry, the high-resolution GTL gas profiles enhance process monitoring, ensure Fischer–Tropsch conversion efficiency and protect expensive catalysts.

Future Trends and Applications

Emerging directions include:

• Integration of real-time, on-line breath analyzers for point-of-care diagnostics.
• Advanced detector combinations (e.g., pulsed discharge TCD, sulfur chemiluminescence) for extended dynamic range.
• Automated sample handling and data processing through AI-driven chromatography software.
• Miniaturized GC systems for field or bedside applications.

Conclusion

By customizing classical gas chromatography systems with multiple detectors and tailored sampling interfaces, Wasson-ECE Instrumentation demonstrated robust analytical solutions for both biomedical breath studies and complex industrial gas streams. The approaches described achieve low-ppm sensitivity, reliable quantitation and streamlined workflows, illustrating the versatility of GC-based trace analysis.