Detection of Sulfur-Containing Metabolites of Asparagus in Urine by SBSE-GCxGC-TOFMS

Importance of the Topic

Understanding the generation and detection of sulfur-containing metabolites from asparagus in urine provides insights into human metabolomics and offers a model for tracking dietary biomarkers. Efficient detection of these compounds can support research in nutrition science, diagnostic metabolomics and quality control of extraction methods.

Objectives and Overview of the Study

This work aims to develop a rapid, solvent-free sample preparation and analysis workflow for detecting characteristic sulfur metabolites derived from asparagusic acid in human urine. By leveraging stir-bar sorptive extraction (SBSE) coupled with comprehensive two-dimensional gas chromatography time-of-flight mass spectrometry (GCxGC-TOFMS), the study compares pre- and post-asparagus urine profiles to identify key volatile compounds.

Methodology and Instrumentation

Urine samples were collected from volunteers before and 90–120 minutes after asparagus consumption. Each 250 mL aliquot underwent SBSE using a polydimethylsiloxane-coated stir bar at 800 rpm. The stir bars were thermally desorbed in a GERSTEL Twister Desorption Unit (TDU) into a cooled inlet system (CIS 4). The analytes were then transferred onto a LECO Pegasus 4D GCxGC-TOFMS system comprising:

• Primary column: GERSTEL-MACH LTM, 10.0 m × 0.18 mm ID × 0.20 µm df (Rtx-5)
• Secondary column: 1.00 m × 0.10 mm ID × 0.10 µm df (DB-17ms)
• Dual-jet thermal modulator with +30 °C offset
• Carrier gas: helium at 1.5 mL/min constant flow
• Transfer line and CIS interface maintained at 280 °C
• TOFMS acquisition at full mass range enabling True Signal Deconvolution

Thermal programs included splitless desorption in the TDU (30 °C to 280 °C) and rapid GC ramps for both one-dimensional and two-dimensional analyses.

Main Results and Discussion

Overlay of one-dimensional chromatograms revealed several volatiles present exclusively in post-asparagus urine, including acetone, acetic anhydride, and various ketones and aromatic compounds. GCxGC contour plots highlighted distinct sulfur metabolites such as S-methyl propene thioate and 1,4-bis(methylthio)butane. S-methyl 2-propenethioate was detected at 205 s (1D) and 1.7 s (2D) with high spectral similarity (863) to library references. The comprehensive separation reduced coelutions and allowed accurate quantitation through deconvolution.

Benefits and Practical Applications

The SBSE-GCxGC-TOFMS approach eliminates solvent use, shortens extraction time, and automates sample processing via the GERSTEL MPS 2–TDU–CIS4 platform. Enhanced chromatographic resolution and high-speed mass spectral acquisition enable sensitive detection of trace sulfur metabolites. This workflow can be applied in metabolomic profiling, clinical diagnostics, nutritional studies, and quality control in food and environmental analysis.

Future Trends and Applications

Advancements may include:

• Integration with high-resolution mass spectrometers for exact-mass identification
• Miniaturized SBSE devices for point-of-care or field analysis
• Expansion to other classes of biomarkers and biological matrices
• Data-driven deconvolution algorithms leveraging machine learning
• Coupling with direct sampling techniques such as SPME or ambient desorption

Conclusion

The combined SBSE and GCxGC-TOFMS platform delivers a rapid, solvent-free, and highly resolved method for profiling sulfur-containing metabolites of asparagus in urine. Automation and advanced deconvolution further streamline analysis, making this approach valuable for diverse applications in metabolomics and analytical chemistry.

References

Stevens P. Detection of Sulfur-Containing Metabolites of Asparagus in Urine by SBSE-GCxGC-TOFMS. LECO Corporation Application Note, Form No. 203-821-325, 2007.