Preparation of a particle-loaded membrane for trace gas sampling.

A divinylbenzene (DVB) particle-loaded membrane with high extraction capacity was prepared using the bar coating method. The prepared membrane was evaluated in terms of morphology, effect of particle ratio, and membrane size on extraction efficiency, as well as linear calibration curve and limit of detection. The SEM (scanning electron microscope) images showed that the DVB particles were uniformly distributed in the PDMS base, ensuring the repeatability of the membranes. The extraction amount was quantified by gas chromatography-mass spectrometry coupled with a thermal desorption unit. Results showed that the extraction efficiency of the prepared membrane increased about 2 orders of magnitude for benzene sampling as the particle ratio increased from 0% to 30%, and the extraction amount was linearly proportional to the size of the membrane. A comparison with a pure PDMS membrane and DVB/PDMS fiber for outdoor air sampling showed that the extraction efficiency of the DVB/PDMS membrane was significantly enhanced, especially for volatile and polar compounds. The limit of detection was about 0.03 ng/mL for benzene in air, and the linear dynamic range extended to 100 ng/mL. An equilibrium calibration method was proposed for low-level air pollutant sampling using this high capacity membrane, and a displacement effect was not observed. To demonstrate the power of the technique, the developed approach was applied to monitor both spot and time weighted average (TWA) concentrations of benzene in outdoor air. A high spot concentration of benzene was observed in morning and afternoon rush hours, with TWA concentrations of 10.7 ng/L measured over the 11-h monitoring period.