GC-MS of Volatile Organic Compounds Using Purge and Trap Extraction

Keywords compound specific isotope analysis, VOC, purge and trap, sources of contamination, degradation pathways 

The compound specific isotope analysis (CSIA) has been successfully used in the assessment of in situ remediation of contaminated environments, identification of pollutant degradation pathways, or the verification of contaminant sources. In these types of studies, the sensitivity of isotope ratio monitoring GC-MS (irm-GC-MS) is often a limiting factor, since concentrations of organic contaminants in groundwater are very often in the low pg/L range. Hence, in order to be able to routinely use irm-GC-MS techniques in environmental studies, efficient extraction procedures are required. 

While P T, providing the lowest MDLs for VOCs, is a routinely used extraction method for the trace level quantification, the on-line coupling with irm-GC-MS has rarely been reported (Schmidt et al, 2004). 

Since the P T procedure includes various phase transition steps that may shift the isotopic signature of the analytes (evaporation, sorption and condensation), the P T method parameters of purge time, desorption time and injection temperature have been carefully evaluated for the determination of the 8 C-values. The compound specific isotope ratios of 10 different VOCs ranging from the unpolar benzene to the polar MTBE as listed in Table 4.6 were determined (Zwank, 2003 Zwank and Berg, 2013). 

Sample concentration System Tekmar purge and trap concentrator LSC 3100 

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Zwank, L. and Berg, M. (2013) Enhanced Method Detection Limits for irm-GC-MS of Volatile Organic Compounds Using Purge and Trap Extraction., Application Note 30053, Thermo Electron. 

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