Optimization of EPA Method 325 for the Fast, Accurate and Precise Monitoring of VOCs Around Oil Refinery Fencelines

Importance of the Topic

Monitoring volatile organic compounds (VOCs) at refinery fencelines is critical for ensuring compliance with U.S. EPA regulations and protecting air quality and public health.

Objectives and Study Overview

This study aimed to optimize a single thermal desorption–gas chromatography/mass spectrometry (TD-GC/MS) method capable of analyzing both VOCs and semi-volatile organic compounds (SVOCs) in one sequence while detailing the sampling requirements defined by EPA Method 325A and 325B for refinery fenceline monitoring.

Methodology and Instrumentation

Sampling methodology

• Passive TD tubes packed with porous graphitized carbon (Carbopack X) deployed in weather-protected shelters along the fenceline for 14-day periods, 26 events per year
• Sampling locations determined by two options in Method 325A: reference angles from facility center (Option 1) or perimeter spacing (Option 2), with additional field blanks, duplicates, and source samples
• Onsite or nearby weather station data logged hourly (wind speed, direction, temperature, pressure)

Instrumental setup

• TurboMatrix Automated Thermal Desorber for tube conditioning and primary/secondary desorption onto Peltier-cooled trap
• PerkinElmer Clarus SQ8 GC/MS operated in full-scan MS mode to minimize false positives
• Fast GC temperature program achieving baseline separation of target compounds (benzene to trimethylbenzenes) in under 3.3 minutes

Main Results and Discussion

Under optimized TD and GC/MS parameters, seven representative analytes (including benzene) eluted within 1.5–3.2 minutes. Method performance met EPA 325B criteria with high precision (RSD <3 %), linearity (r > 0.999), and signal-to-noise ratios (>500:1 at 0.2 ng). Uptake rates for 19 target VOCs on Carbopack X tubes ranged from 0.45 to 0.67 mL/min, confirming reliable passive sampling.

Benefits and Practical Applications

The unified TD-GC/MS approach enables simultaneous analysis of VOCs and SVOCs, reducing instrument changeover and labor while maintaining regulatory compliance. Reusable TD tubes and automated conditioning increase throughput and cost efficiency for environmental laboratories.

Future Trends and Potential Applications

Emerging developments may include integration of miniaturized or real-time passive sensors, advanced data analytics for spatial–temporal VOC distributions, expanded analyte libraries for emerging pollutants, and field-deployable TD-based systems for remote monitoring.

Conclusion

The optimized TD-GC/MS methodology fulfills EPA Method 325 requirements with enhanced speed, reliability, and flexibility, supporting effective fenceline monitoring of refinery emissions.

Reference

• U.S. EPA. Method 325A: Volatile Organic Compounds from Fugitive and Area Sources. Sampler Deployment and VOC Sample Collection.
• U.S. EPA. Method 325B: Volatile Organic Compounds from Fugitive and Area Sources. Sampler Preparation and Analysis.
• DeWees J. M. Refinery Fenceline Monitoring & Method 325A/B, U.S. EPA OAQPS Measurement Technology Group Workshop, 2015.
• U.S. EPA. Compendium Method TO-17: Determination of VOCs in Ambient Air Using Active Sampling on Sorbent Tubes, 1999.
• Varisco S. et al. Extending the Hydrocarbon Range for Soil Gas Analysis Using Automated Thermal Desorption-GC/MS. LCGC North America, 2016.