Effectiveness of the MonoTrap Collection Method for VOC Analysis in Exhaled Breath Using GC-MS

Significance of the topic

The analysis of volatile organic compounds (VOCs) in exhaled breath is a minimally invasive approach with growing importance for metabolic, inflammatory and oncological research. Breathomics offers the potential for early disease detection, longitudinal monitoring and population-scale screening. Reliable, practical sampling methods that preserve trace-level VOCs and enable decentralized collection are essential to translate breath analysis into routine research and clinical workflows.

Objectives and study overview

This application study compared two breath sampling approaches—Tenax thermal desorption tubes (active transfer from a sampling bag) and MonoTrap silica-monolith adsorbent (passive/static adsorption in a sampling bag)—to evaluate which provides broader and more reproducible VOC coverage when coupled with thermal desorption GC–MS. The work also assessed MonoTrap performance for differentiating VOC profiles between healthy volunteers and subjects with inflammatory conditions. The study emphasized method practicality for remote sampling and transportability of collected samples.

Used instrumentation

The principal instruments reported:

• Thermal desorption unit: TD-30R (tube and trap desorption stages).
• Gas chromatograph–mass spectrometer: GCMS-QP2020 NX.
• Column: SH-Rxi-5Sil MS (30.0 m × 0.25 mm I.D., 0.1 μm film).
• Adsorbents: Tenax TA tubes (1/4" × 3.5", Tenax TA 35/60) and MonoTrap (RGC 18TD, silica monolith, GL Sciences).
• Internal standard: toluene-d8 added during TD conditioning to monitor analytical stability.

Methodology and analytical conditions

Sampling:

• Tenax approach: Subjects exhaled into a 2 L sampling bag; the bag contents were actively passed through a Tenax tube at 100 mL/min to capture VOCs.
• MonoTrap approach: A MonoTrap device was placed inside a 2 L sampling bag; subjects exhaled directly into the bag and the MonoTrap was left static within the bag for either 3 hours or 24 hours to adsorb VOCs. After exposure, MonoTraps were sealed in GC vials for transport.

Thermal desorption and GC–MS conditions (selected highlights):

• TD settings: tube desorb 250–350 °C, flow 60 mL/min, trap cooling to −20 °C, trap desorb 250 °C for 5 min, Tenax-TA used for trap tubes.
• GC program: initial 60 °C (1 min), ramp 5 °C/min to 200 °C, then 30 °C/min to 320 °C (2 min).
• Injection: split mode, split ratio 10, helium carrier with linear velocity 36.5 cm/s.
• MS: electron ionization scan mode, m/z 35–600, ion source 230 °C, interface 280 °C, event time 0.3 s.

Quality control:

• Toluene-d8 was introduced as an internal standard to assess desorption and instrument stability across runs.

Main results and discussion

Key findings:

• Detected peak counts: For the same healthy-subject breath, Tenax captured 58 peaks. MonoTrap captured a similar number after 3 h exposure but markedly more after 24 h (152 peaks), indicating superior cumulative capture with prolonged static sampling.
• MonoTrap adsorption dynamics: Using two MonoTraps at 3 h increased peak intensities (suggesting higher capacity or loading), whereas at 24 h a single MonoTrap provided comparable peak numbers and intensities—implying adsorption equilibrium or sufficient capacity over extended static periods.
• Profile differences between cohorts: VOC profiles differed between healthy subjects and those with inflammatory conditions across multiple compounds and overall chromatographic patterns (examples included variations in dimethyl dodecane and methyl propyl nonane). These differences demonstrate the system’s ability to detect altered VOC patterns but were not presented as diagnostic markers.

Interpretation and technical considerations:

• Passive MonoTrap sampling increases sensitivity by extending exposure time without requiring pumps, making it attractive for remote and decentralized collection.
• MonoTrap’s silica-monolith architecture provides a large surface area and broad adsorption range (low to medium/high boiling VOCs), improving compound coverage compared with single-bed Tenax sampling via flow-through at limited volumes.
• Transport and storage: MonoTrap can be sealed in GC vials for straightforward transport from collection sites to centralized labs.
• Limitations: the study does not provide large cohort statistics, breakthrough volumes, water/vapor effects, long-term storage stability data, nor absolute quantification—factors important for standardization and clinical translation.

Benefits and practical applications

Practical advantages identified:

• Pump-free, passive sampling simplifies logistics for field studies, point-of-care settings, and geographically distributed cohort collection.
• Enhanced VOC coverage after extended static sampling increases discovery power for breathomics and biomarker research.
• Ease of sample transport and integration with established TD–GC–MS workflows facilitates centralized high-sensitivity analysis.

Potential application areas:

• Breathomics biomarker discovery for inflammatory, metabolic and oncologic diseases.
• Large-scale epidemiological studies and remote clinical research where active sampling is impractical.
• Environmental exposure and occupational monitoring using human or ambient air sampling.

Future trends and potential applications

Expected developments to improve and expand this approach:

• Standardization: development of agreed protocols for breath collection time, trap type, internal standards and storage to improve inter-study comparability.
• Quantitation and QC: incorporation of multiple isotopically labeled standards and calibration strategies to allow semi-quantitative or quantitative breath VOC measurements.
• Analytical advances: coupling MonoTrap desorption with high-resolution MS or comprehensive GC×GC–MS to enhance compound identification and separation of coeluting species.
• Data analytics: application of machine learning and multivariate pattern recognition to identify reproducible VOC signatures across larger cohorts.
• Miniaturization and point-of-care: development of portable TD–GC–MS or trap designs for near-patient testing and rapid screening workflows.

Conclusion

The MonoTrap passive collection method combined with TD–GC–MS provides an effective, practical alternative to active Tenax tube sampling for exhaled breath VOC profiling. Extended static exposure (24 h) with a single MonoTrap substantially increases detectable VOCs versus the Tenax flow-through approach and supports remote, pump-free sampling. The workflow demonstrates potential for breathomics studies and decentralized sample collection, while further standardization, quantitative method development and larger cohort validation are needed before clinical application.

References

1. Tsutsui K, Nemoto M, Kono M, Sato T, Yoshizawa Y, Yumoto Y, Nakagawa R, Iwamoto T, Wada H, Sasaki T. GC-MS analysis of exhaled gas for fine detection of inflammatory diseases. Analytical Biochemistry. June 2023.
2. Gashimova E, Osipova A, Temerdashev A, Porkhanov V, Polyakov I, Perunov D, Dmitrieva E. Exhaled breath analysis using GC-MS and an electronic nose for lung cancer diagnostics. Analytical Methods. October 2021.
3. Di Gilio A, Palmisani J, Nisi M, Pizzillo V, Fiorentino M, Rotella S, Mastrofilippo N, Gesualdo L, de Gennaro G. Breath Analysis: Identification of Potential Volatile Biomarkers for Non-Invasive Diagnosis of Chronic Kidney Disease (CKD). Molecules. October 2024.