Compound Specific Isotope Ratio Analysis in Vapour Intrusion Studies using Waterloo Membrane Sampler (WMS)
Goli, Oana Cristina
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Compound specific isotope analysis (CSIA) has been used extensively for fingerprinting applications and for the evaluation of the degradation processes in organic contaminant studies in groundwater. Recently, an increase in academic interest on the potential applications of CSIA in vapour intrusion has been observed, and various studies have been conducted. A key challenge of this research is the development of analytical protocols for CSIA that handle very low concentrations of organic compounds typically found in indoor samples. A sampling device capable of gathering enough mass for CSIA has to be tested for field applications. In this research the Waterloo Membrane Sampler (WMS), a permeation-type passive sampler that has been successfully used in numerous studies, is presented as a potential device for this purpose. Indeed, the WMS has been successfully applied in the quantitation of volatile analytes in indoor and outdoor air, as well as soil-gas matrices. The objective of this research was to evaluate the applicability of the WMS for CSIA in vapour intrusion studies. Analyte amounts sufficient for CSIA were collected when using thermal desorption to introduce the sample into the gas chromatography-isotope ratio mass spectrometry system (TD-GC-IRMS). The TD-GC-IRMS was employed to determine the stable carbon isotopic composition (δ13C) of three model analytes: hexane, benzene and trichloroethylene, which were contained in a standard gas mixture. In order to determine whether isotopic fractionation occurred during the exposure, measures of δ13C were taken for individual compounds found in both the standard gas (active sampling) and in the gas permeating through the PDMS membrane into the sorbent (passive sampling). Various WMS were exposed to the standard gas for 3, 6, 12, 24, 48, 96 and 192 hours. Variations of the isotopic carbon composition for each analyte were measured versus time, amount of analytes sorbed and exposure temperature. Results obtained in all studies indicate good reproducibility with a standard deviation within the accepted analytical error of ± 0.5 ‰. All sampling processes introduced small isotopic fractionation; however, the degree of fractionation remained practically constant and independent of sampling time, mass adsorbed and temperature, therefore could be accounted for. The new method developed was applied in a field study, where the results obtained were compared with solvent base active sample collection and analysis. Results obtained demonstrated good data reproducibility. This indicates that CSIA coupled with WMS could be a valuable tool in environmental forensics field.