The role of sample collection method and the bias between different standard matrices in the determination of volatile organic compounds in air

This study was undertaken to assess the relative bias between two types of sampling methods for volatile organic compounds (VOCs), i. e., sorbent tube vs. bag sampling methods and between different standard phases. For the purpose of this comparative study, gaseous standards containing three major aromatic VOCs (benzene, toluene, and xylene-commonly called BTX) were analyzed by thermo-desorption gas chromatography (TD-GC) with flame ionization detector. According to our findings, the relative response of target compounds can be smaller in the bag method than in the tube method. Although the relative bias varies with the sample transfer conditions for the TD, the mean slope values of the former are smaller by up to 20% relative to the latter, possibly due to sorptive loss on the bag sampler. In addition, the effects of different standard matrices (i. e. liquid and gas phases) were also examined using the sorbent tube method. The results indicated that the slope values of the gas-phase standard were smaller by half (about 43-56%) than the liquid-phase standard. Consequently, information concerning the extent of relative bias between sampling methods (e. g., bag and tube) or standard matrices (e. g., gas and liquid) should be considered as one of the key factors in TD applications.