ARS | Publication request: The use of permeation tube device and the development of empirical formula for accurate permeation rate

Submitted to: Journal of Chromatography A
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 8, 2011
Publication Date: December 12, 2011
Citation: Susaya, J., Kim, K., Cho, J., Parker, D.B. 2011. The use of permeation tube device and the development of empirical formula for accurate permeation rate. Journal of Chromatography A. 1218:9328-9335.

Interpretive Summary: Permeation tube devices are used to generate trace gases for calibrating air quality instruments used for odor and chemical emissions analyses. Concentrations in the parts per million to parts per billion ranges are achieved by adjusting the temperature or air flow rate across the permeation tube. A series of laboratory experiments were conducted to assess the accuracy of permeation tube devices. Air concentrations based on equations provided by the permeation tube manufacturer were up to 54 percent different than measured concentrations. New equations were derived using regression analyses. The new equations resulted in predicted concentrations within one percent of measured concentrations, greatly improving the accuracy of permeation tube devices.

Technical Abstract: A series of laboratory experiments were conducted to assess the accuracy of permeation tube (PT) devices using a calibration gas generator system to measure permeation rate (PR) of volatile organic compounds (VOCs). Calibration gas standards of benzene, toluene, and m-xylene (BTX) were produced from PTs at varying flow rates (FR) of 20 to 1200 mL min-1 and constant temperature (30°C). Results indicate that changes in FR greatly affected the PR of each VOC at this temperature. This paper presents experimental approaches to accurately measure actual PR (APR) and the derivation of empirical equations for predicted PR (PPR). If the magnitude of bias is defined as the difference between PPR and the manufacturer’s PR (MPR), the bias was typically 19-40% for toluene (T) and 31-54% for m-xylene (X). Benzene (B) exhibited the least bias of 1.4-18.8%, nevertheless our PPR values for B were more reliable at lower flow rates (0.75-1.20 %). This study highlights the importance of FR and associated pressure changes as a key to accurate PR estimation from PT devices.