Sample integrity evaluation and EPA method 325B interlaboratory comparison for select volatile organic compounds...

Area of Science:

• Environmental Science
• Analytical Chemistry
• Occupational Health

Background:

• U.S. Environmental Protection Agency (EPA) Methods 325A and 325B are used for diffusive monitoring of benzene and volatile organic compounds (VOCs).
• Carbopack X sorbent tubes are employed for collecting these VOCs.
• Standard operating procedures specify a maximum 30-day storage for collected samples.

Purpose of the Study:

• To evaluate the sample integrity of VOCs collected on Carbopack X sorbent tubes.
• To conduct an interlaboratory comparison of VOC analysis using EPA Methods 325A and 325B.
• To assess the feasibility of extending the recommended sample storage duration.

Main Methods:

• VOC samples were stored under refrigeration for up to 240 days.
• Sample analysis was performed using thermal desorption/gas chromatography-mass spectrometry (TD/GC-MS).
• Three commercial laboratories participated in an interlaboratory comparison, analyzing field and laboratory-collected VOC samples according to Method 325B.

Main Results:

• Refrigerated VOC samples on Carbopack X tubes demonstrated stability for 6 months or longer.
• Interlaboratory comparison results for laboratory-collected samples were within ±25% of theoretical concentrations.
• Differences among laboratories for ambient samples were minimal (<1 ppbv), indicating good precision and agreement.

Conclusions:

• The 30-day storage limitation for VOCs collected on Carbopack X tubes may be extended, reducing logistical constraints.
• EPA Methods 325A and 325B are reliable for diffusive VOC monitoring, with consistent results across multiple laboratories.
• The study supports the extended use of refrigerated Carbopack X passive samplers for environmental monitoring.