Kinetic Study of Membrane Extraction with a Sorbent Interface for Air Analysis

This paper presents the theory and experimental implementation of the technique of membrane extraction with a sorbent interface for air analysis. A mathematical model was derived to predict the extraction process and the significant factors, such as membrane length and carrier gas flow rate. A benzene/nitrogen standard gas mixture was generated by the permeation tube method. Several parameters that affect the extraction efficiency are discussed. Among them, the membrane length, the flow rate of the carrier gas, and temperature strongly affected the extraction rate of analyte. The results demonstrated that the extraction rate of benzene was decreased with increase of the extraction temperature. Toluene, hexane, ethylbenzene, and trichloroethylene were selected to test the theory, and good agreement between theoretical predictions and experimental results was observed. The estimation of air concentration without experimental calibration is discussed. In the proposed estimation method, the diffusion coefficient of benzene in the membrane and the distribution constant between air and the membrane were measured experimentally.