Bouchard Daniel, Wanner Philipp, Luo Hong, McLoughlin Patrick W, Henderson James K, Pirkle Robert J, Hunkeler Daniel
Centre for Hydrogeology and Geothermics (CHYN), University of Neuchâtel, Rue Emile Argand 11, 2000 Neuchâtel, Switzerland.
Centre for Hydrogeology and Geothermics (CHYN), University of Neuchâtel, Rue Emile Argand 11, 2000 Neuchâtel, Switzerland.
J Chromatogr A. 2017 Oct 20;1520:23-34. doi: 10.1016/j.chroma.2017.08.059. Epub 2017 Aug 24.
The methodology of the solvent-based dissolution method used to sample gas phase volatile organic compounds (VOC) for compound-specific isotope analysis (CSIA) was optimized to lower the method detection limits for TCE and benzene. The sampling methodology previously evaluated by [1] consists in pulling the air through a solvent to dissolve and accumulate the gaseous VOC. After the sampling process, the solvent can then be treated similarly as groundwater samples to perform routine CSIA by diluting an aliquot of the solvent into water to reach the required concentration of the targeted contaminant. Among solvents tested, tetraethylene glycol dimethyl ether (TGDE) showed the best aptitude for the method. TGDE has a great affinity with TCE and benzene, hence efficiently dissolving the compounds during their transition through the solvent. The method detection limit for TCE (5±1μg/m) and benzene (1.7±0.5μg/m) is lower when using TGDE compared to methanol, which was previously used (385μg/m for TCE and 130μg/m for benzene) [2]. The method detection limit refers to the minimal gas phase concentration in ambient air required to load sufficient VOC mass into TGDE to perform δC analysis. Due to a different analytical procedure, the method detection limit associated with δCl analysis was found to be 156±6μg/m for TCE. Furthermore, the experimental results validated the relationship between the gas phase TCE and the progressive accumulation of dissolved TCE in the solvent during the sampling process. Accordingly, based on the air-solvent partitioning coefficient, the sampling methodology (e.g. sampling rate, sampling duration, amount of solvent) and the final TCE concentration in the solvent, the concentration of TCE in the gas phase prevailing during the sampling event can be determined. Moreover, the possibility to analyse for TCE concentration in the solvent after sampling (or other targeted VOCs) allows the field deployment of the sampling method without the need to determine the initial gas phase TCE concentration. The simplified field deployment approach of the solvent-based dissolution method combined with the conventional analytical procedure used for groundwater samples substantially facilitates the application of CSIA to gas phase studies.
用于采集气相挥发性有机化合物（VOC）以进行化合物特异性同位素分析（CSIA）的溶剂溶解法的方法学得到了优化，以降低三氯乙烯（TCE）和苯的方法检测限。先前由[1]评估的采样方法是将空气抽过一种溶剂，以溶解并积累气态VOC。采样过程结束后，然后可以像处理地下水样品一样处理溶剂，通过将一份溶剂稀释到水中以达到目标污染物所需浓度来进行常规CSIA。在所测试的溶剂中，四甘醇二甲醚（TGDE）在该方法中表现出最佳适用性。TGDE与TCE和苯具有很强的亲和力，因此在化合物通过溶剂的过程中能有效地溶解它们。与之前使用的甲醇相比，使用TGDE时TCE（5±1μg/m）和苯（1.7±0.５μg/m）的方法检测限更低（之前甲醇对TCE的检测限为385μg/m，对苯的检测限为130μg/m）[2]。方法检测限是指将足够质量的VOC加载到TGDE中以进行δC分析所需的环境空气中的最低气相浓度。由于分析程序不同，发现与δCl分析相关的TCE的方法检测限为156±6μg/m。此外，实验结果验证了采样过程中气相TCE与溶剂中溶解的TCE的逐步积累之间的关系。因此，基于气-溶剂分配系数、采样方法（例如采样率、采样持续时间、溶剂量）以及溶剂中TCE的最终浓度，可以确定采样事件期间存在的气相TCE浓度。此外，在采样后分析溶剂中TCE浓度（或其他目标VOC）的可能性使得该采样方法能够在现场部署，而无需确定初始气相TCE浓度。基于溶剂的溶解法的简化现场部署方法与用于地下水样品的传统分析程序相结合，极大地促进了CSIA在气相研究中的应用。
