Measurement of VOCs by Thermal Desorption GC-MS Using Hydrogen Carrier Gas

Significance of the Topic

Volatile organic compounds (VOCs) are key indicators of air quality in industrial, urban and indoor settings. Traditional GC–MS workflows rely on helium, a gas facing supply shortages and rising costs. Adopting hydrogen as an alternative carrier streamlines operations, reduces expenses and ensures uninterrupted VOC monitoring.

Objectives and Study Overview

This study evaluates the performance of a TD-30R thermal desorption unit coupled to the GCMS-QP2020 NX using hydrogen carrier gas. The goal is to assess linearity, repeatability and overall suitability of hydrogen for routine VOC analysis, comparing results with established helium-based methods.

Materials and Methods

Mixed standards of seven VOCs (toluene, ethylbenzene, o-, m-, p-xylene, styrene, p-dichlorobenzene and tetradecane) were prepared in methanol at concentrations from 10 mg/L to 1000 mg/L. One microliter of each dilution was loaded onto TENAX-TA trap tubes. Thermal desorption was performed at 280 °C (10 min) with nitrogen purge, followed by trap desorption at 250 °C. GC separation used an SH-I-5Sil MS column with hydrogen at 80 kPa pressure in split mode (20:1). Mass spectrometry acquired full scan data (m/z 20–600).

Instrumentation

• GC–MS: Shimadzu GCMS-QP2020 NX
• Autosampler: TD-30R thermal desorption system
• Column: SH-I-5Sil MS, 30 m × 0.25 mm × 0.25 µm
• Carrier gas: Hydrogen, controlled by pressure (80 kPa)
• MS conditions: Ion source 200 °C; interface 230 °C; scan mode, 0.3 s event time

Results and Discussion

Repeatability tests at 100 ng injection showed RSD values below 5 % for all compounds. Calibration curves spanning 10 ng–1000 ng delivered correlation coefficients (R²) above 0.996, with toluene reaching R² of 0.9989 and R of 0.9995. Mass chromatograms confirmed clear separation and stable response factors, demonstrating hydrogen’s efficacy despite slight sensitivity differences compared to helium.

Benefits and Practical Applications

• Eliminates solvent extraction, boosting throughput and reducing labor.
• Hydrogen supplies are cost-effective and abundant.
• Comparable analytical performance to helium methods for target VOCs.
• Facilitates continuous monitoring programs even during helium shortages.

Future Trends and Opportunities

Expanding hydrogen-based workflows to broader VOC panels and environmental matrices, integrating on-line thermal desorption systems for real-time monitoring, and combining hydrogen carriers with advanced detectors (e.g., high-resolution MS) will improve sensitivity and selectivity. Ongoing optimization of trap materials and desorption parameters will further enhance method robustness.

Conclusion

This work demonstrates that thermal desorption GC–MS with hydrogen carrier gas on Shimadzu TD-30R+GCMS-QP2020 NX achieves reliable repeatability and linearity for common VOCs. Careful method development is essential when substituting carrier gases. Laboratories facing helium constraints can adopt hydrogen to maintain analytical performance and operational continuity.