Monitoring VOCs in Stationary Source Emissions Using Sorbent Tubes with Analysis by TD-GC/MS in Accordance with Chinese EPA Method HJ 734-2014

Importance of the Topic

Volatile organic compounds (VOCs) are key contributors to photochemical smog, ozone formation and particulate pollution, and many VOCs pose direct health risks as hazardous air pollutants. Monitoring VOC emissions from stationary industrial sources is critical for regulatory compliance, air-quality management and public health protection, driving the development of sensitive, reliable and automatable analytical protocols.

Objectives and Overview

This study presents the performance of an automated, cryogen-free thermal desorption–gas chromatography–mass spectrometry (TD-GC/MS) system for the analysis of VOCs in stationary source emissions. The method follows Chinese EPA Method HJ 734-2014 and demonstrates automated quantitative re-collection of split flows to support repeat analysis, method validation and result verification.

Methodology and Instrumentation Used

Standards and Sampling

• Calibration standards of 22 VOCs in methanol diluted to 5–100 µg/mL (equivalent to 4.2–83 ppbv in 300 mL air) with internal standards (trifluoromethylbenzene and bromofluorobenzene at 50 µg/mL).
• Sample collection onto conditioned sorbent tubes using an ACTI-VOC low-flow pump at 50 mL/min for 6 minutes (300 mL).

Thermal Desorption and GC/MS

• TD System: Markes TD100-xr with universal sorbent tubes and air-toxics focusing trap.
• Tube desorption: 300 °C, 5 minutes; trap held at 25 °C then heated to 250 °C at maximum rate.
• Outlet split: 7.7:1 (adjustable for high-concentration samples up to 33:1).
• GC Columns: Agilent DB-1 (30 m × 0.25 mm, 1 µm) or DB-624 (60 m × 0.32 mm, 1.4 µm).
• Oven program: optimized to reduce analysis time from 30 to 12 minutes while maintaining separation.
• MS Conditions: Electron impact ionization, full scan m/z 36–180 then 33–270.

Main Results and Discussion

Chromatographic Performance

• Sharp, symmetrical peaks across polarity and volatility range, including polar analytes (e.g., isopropanol) and late-eluting compounds.
• Fast temperature ramps improved peak shape and reduced runtime.

Linearity, Reproducibility and Detection Limits

• Excellent linearity for 22 target compounds over 5–100 µg/mL (R2 > 0.99).
• Retention time RSDs < 0.1%, peak area RSDs < 8% (n=8).
• Method detection limits 0.002–0.016 µg/m³ (4–83 ppbv in 300 mL).

High-Concentration Samples

• Outlet split up to 33:1 for analytes at 100–1 000 µg/mL, with carryover below 0.5%.

Quantitative Re-collection

• Automated re-collection of split flows onto clean sorbent tubes yields recoveries matching theoretical split ratios over multiple cycles, facilitating method validation.

Real-World Emission Sample

• Analysis of 300 mL of restaurant exhaust detected 16 HJ 734 target compounds, including trace-level VOCs, demonstrating practical applicability.

Benefits and Practical Applications

• Full compliance with Chinese EPA Method HJ 734-2014 and compatibility with HJ 644-2013 and US EPA TO-17.
• Cryogen-free operation reduces maintenance and operating costs.
• Automated sample preparation, desorption, split, re-collection and reanalysis improve throughput and data confidence.
• Wide analyte range (C2–C44, polar and nonpolar) supports diverse emission monitoring needs.

Future Trends and Applications

• Integration with other regulatory methods and real-time field deployable TD units.
• Extension to semivolatile organics and reactive species trapping.
• Enhanced data analysis using machine learning for rapid source apportionment.
• Miniaturization and on-line coupling with air-quality monitoring networks.

Conclusion

Markes International’s automated, cryogen-free TD-GC/MS platform delivers high sensitivity, robust reproducibility and efficient sample handling for monitoring VOC emissions from stationary sources in accordance with HJ 734-2014. Automated quantitative re-collection and flexibility in split ratios simplify method validation and ensure reliable, repeatable results.

References

• Chinese EPA Method HJ 734-2014: Stationary source emission determination of VOCs by sorbent adsorption and TD-GC/MS.
• Chinese EPA Method HJ 644-2013: Ambient air VOC determination by sorbent adsorption and TD-GC/MS.
• US EPA Method TO-17: Sorbent tube sampling and TD-GC/MS for air toxics.
• Markes International TD100-xr and associated sorbent tube accessories.
• Application Note 117, Agilent Technologies, 2017 (5991-8268EN).