Storage Time Study of Passive Sampling Tubes Used for EPA Method 325

Best Practices in Indoor and Outdoor Air Monitoring
Oral Presentation

Prepared by , O. Shimelis, J. McCleerey, M. Ye

Contact Information: [email protected]; 814-359-5917


EPA Method 325 uses thermal desorption tubes packed with a single bed of a graphitized carbon black adsorbent to passively collect air samples along the fenceline of U.S. petroleum refineries. These passive sampling tubes are placed in a shelter to protect the tubes from the weather, and are deployed for 14 days. After sampling the tubes are sealed with long-term metal storage caps, and sent to a laboratory for analysis. The sampling tubes are analyzed using thermal desorption and gas chromatography. The method specifies that the air samples can be stored up to 30 days.

We investigated the sample recovery from spiked tubes by analyzing the tubes after theyíve been placed into storage according to the guidelines in the method. Tubes were spiked with a gas mix containing 60 volatile organic compounds which the molecular weight ranged from Propylene to Hexachlorobutadiene. The spiked tubes were analyzed after they were in placed in storage for 7, 14, 21 and 30 days at both ambient and refrigerated temperatures.

Recoveries of 90% or better were obtained for Benzene and other aromatics from tubes stored for 30 days. The recovery of all the brominated VOCís dropped below 80% after only 14 days of storage. This research also provided a list of other VOCís that are not currently listed in the Method 325, but would be suitable for collection using the same sampling tube.