Characterization of Biogenic Emissions by Online Thermal Desorption Gas Chromatography-Mass Spectrometry

Importance of the topic

Biogenic volatile organic compounds (VOCs) are critical drivers of tropospheric chemistry and ozone formation. On a global scale their emissions exceed anthropogenic sources by an order of magnitude, yet their regional impact on photochemical smog is poorly quantified. Precise, continuous monitoring of plant‐derived VOCs is essential for understanding natural emissions, plant stress responses, and their influence on air quality.

Objectives and study overview

This work describes the development and application of the GERSTEL Online Thermal Desorption System (TDS G) coupled to gas chromatography‐mass spectrometry (GC‐MS). The primary objectives were to enable fast, automated sampling and analysis of airborne biogenic VOCs under both laboratory and field conditions, and to compare its performance with traditional liquid injection methods.

Methods and instrumentation

The system integrates a modified GERSTEL Thermal Desorption unit (TDS G) with a cooled injection system (CIS) and an HP 5890 GC coupled to an HP 5972A quadrupole MS detector. Key features include:

• Dual‐stage adsorbent bed: Tenax TA and Carbotrap to capture C5–C15 terpenoids.
• CIS cryotrapping at –100 °C with valve‐reversing flow to prevent adsorbent breakthrough.
• Automated sample loop: 9 min desorption, 47 min GC run with parallel adsorption of the next sample.
• Calibration via permeation sources for VOCs and deuterated decane internal standard.

Sampling volumes up to 5 L yielded detection limits of 1–5 pptV and reproducibility better than 8%.

Main results and discussion

Comparison of online thermal desorption with liquid injection showed agreement within 10% for normalized monoterpene responses. The TDS G enabled quantitation of low‐boiling compounds like isoprene, which are not accessible by solvent extraction. Some loss of high‐boiling sesquiterpenes was observed due to cold interfaces, which was mitigated by auxiliary heating.

Benefits and practical applications

The TDS G offers:

• Continuous, unattended operation with 1 h cycle time.
• Enhanced sensitivity for trace VOCs in the pptV range.
• Flexibility for laboratory chambers or field campaigns, including mobile laboratories for traffic emissions.
• Compatibility with off‐line autosamplers for traditional headspace or liquid analyses.

Future trends and possibilities of application

Integrating heated interfaces to reduce sesquiterpene losses and expanding to novel adsorbents could further improve recovery. Coupling with high‐resolution MS or two‐dimensional GC promises enhanced compound identification. Real‐time monitoring of plant stress markers and large‐scale field deployments will deepen understanding of biogenic VOC impacts on air quality and climate.

Conclusion

The GERSTEL Online TDS G GC‐MS system demonstrates robust, high‐sensitivity measurement of biogenic VOC emissions with performance comparable to liquid injection methods and superior automation. Its modular design and short analysis cycle make it a versatile tool for both controlled‐environment studies and ambient air monitoring.

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