以固相擴散模式探討管狀被動式採樣器之採樣率與採樣時間的關係

Examination of the Correlation between Uptake Rate and Sampling Time of a Tubular Passive Sampler Using a Solid Phase Diffusion Model

本文利用吸附劑內之擴散模式探討被動式採樣器之採樣率（uptake rate）隨採樣時間變化之關係。藉由張瑞祺等人針對乙酸乙酯、乙酸正丁酯、苯乙烯、對──二甲苯、甲基異丁酮和四氯乙烯等六種有機溶劑在 Tenax-TA 被動式採樣管在 0.5～8 小時之實驗數據，所計算求得的採樣率，與英國安全衛生署（Health & Safety Executive，HSE）之MDHS 80 （Method for Determination of Hazardous Substances 80）提供之採樣率，以及本文之吸附劑內擴散模式進行比較。MDHS 80 對不同有機溶劑提供單一之採樣率，而實驗數據和本文之擴散模式皆顯示採樣率隨採樣時間增長而降低之關係。在採樣時間 0.5～8 小時範圍內，雖然除了苯乙烯外，使用本文擴散模式之採樣率較MDHS 80使用之單一採樣率之平均誤差為大，但在採樣時間 0.5～2 小時範圍內本文擴散模式所計算之採樣率其誤差值皆有明顯降低，其中苯乙烯、乙酸乙酯、對──二甲苯使用本文擴散模式之採樣率較 MDHS 80 使用之單一採樣率之平均誤差為小。

A simple diffusion model has been employed to examine the adsorption kinetics of six organic solvents, i.e. ethyl acetate, n-butyl acetate, styrene, para-xylene, methyl isobutyl ketone, and tetrachloroethylene, adsorbed individually in a passive sampler, packed with Tenax-TA. The uptake rates calculated from experimental data are compared with that taken from MDSH 80 method and from the diffusion model. All experimental and diffusion model results show that uptake rates decrease with sampling time. For the sampling time between 0.5 and 8 hours, the errors of uptake rate of the six organics by the MDHS 80 method are all smaller than that calculated from the diffusion model except for that of styrene. However, the accuracy of simulated results of styrene, ethyl acetate, and para-xylene in the sampling interval of 0.5 and 2 hours are better than that from MDHS 80. The model assumes that the mass transfer resistance is controlled exclusively inside the adsorbent with linear adsorption isotherm. This study provides a primary theoretical basis to investigate the relationship between uptake rate and sampling time.