Water samples
Method brief: The default method for environmental water samples involves extraction/preconcentration using a purge and trap unit. KEI uses the default option of cryofocusing of purge and trap effluent to permit complete transfer of the effluent into the GC column of the instrument. This assures excellent reporting limits for most of typical target VOCs, at 1 µg/L or better (or low tens of µg/L for hydrogen CSIA). VOCs in difficult chromatographic matrices can be analyzed using two-dimensional chromatography.
Isotope ratios: KEI can determine carbon, chlorine, bromine and hydrogen isotope ratios in VOCs. Currently, other elements are not available.
Examples of target compounds:
Chlorinated ethenes (PCE, TCE, DCEs, VC)
Other halocarbons (1,2-dichloroethane, 1,2-dibromoethane, chlorobenzenes, chloroform, carbon tetrachloride)
BTEX, naphthalene, methylnaphthalenes, MtBE and TBA
The list above shows only representative examples and other VOCs can be potentially analyzed. Typically, KEI can determine C isotope ratios for any compound compatible with gas chromatography separation with none or with relatively low method development. Feasibility of hydrogen and chlorine CSIA varies. If your target compound is not listed, contact the lab for availability of service.
Sample requirements:
Water samples should be collected in standard VOA vials and preserved with HCl following the approach of VOCs concentration analysis (USEPA 5030 or similar). MtBE and several less common compounds are susceptible to acid hydrolysis. Such samples should be preserved by increasing pH above 12, using Trisodium phosphate (TSP). Other containers and preservatives must be approved by the lab on case-specific basis. KEI will typically require at least 3 VOA vials to be provided from each monitoring well. The exact count will be confirmed based on the list of target contaminants, isotope ratios and the projected concentrations of the contaminants. We recommend shipping the samples overnight, on ice or with ice packs, following the standard approach for VOCs concentration analysis.
Soil gas samples
Method brief: This section concerns analysis of gas phase VOCs at intermediate to high concentrations. Refer to the next section for information on analysis of gas phase VOCs under 100 ng/L. The default method for soil gas samples in Summa canisters involves preconcentration on carbon adsorbent media and then thermal desorption of the condensate, with the follow up step identical to those applied to aqueous VOCs, including the option for two-dimensional chromatography.
Isotope ratios: KEI can determine carbon, chlorine, bromine and hydrogen isotope ratios in VOCs. Currently, other elements are not available.
Examples of target compounds:
To date KEI and the predecessor lab at the U. Oklahoma analyzed soil gas samples for chlorinated ethenes and benzene. Other VOCs can be feasible with a degree of method optimization, similarly as discussed in the context of CSIA of aqueous VOCs (contact the lab for availability of service).
Sample requirements:
KEI recommends collecting soil gas samples in Summa canisters, following the standard approach of USEPA TO-15 (the canisters must be provided by the client, e.g., rented from a third-party environmental lab). Other sampling methods with peer-reviewed validation can be accepted on a case-by-case basis, provided they are appropriate for the sample's actual concentration range. KEI is equipped to handle other sampling media such as methanol traps or adsorbent tubes. KEI will typically require one to two Summa canisters to be provided from each monitoring point. The exact count and the canister volume will be confirmed based on the list of target contaminants, isotope ratios and the projected concentrations of the contaminants. Rapid shipping and refrigeration are not necessary for this type of samples.
Indoor air samples
Method brief: This section concerns analysis of gas phase VOCs at low concentrations. Gas phase VOCs are preconcentrated in the field from as much as 100L of air, using active sampling into carbon adsorbent tubes. Adsorbent tubes are then analyzed by KEI using thermal desorption, with the follow up step identical to those applied to aqueous VOCs. In practice, this type of samples always requires two-dimensional chromatography since target compounds reside within a complex matrix of volatiles degassing from indoor surfaces.
Isotope ratios: KEI can determine carbon, chlorine, and hydrogen isotope ratios in VOCs. Currently, other elements are not available.
Examples of target compounds:
Existing validation of the sample preconcentration methodology for sample volumes approaching the recommended maximum of 100L is available exclusively for trichloroethene (TCE), tetrachloroethene (PCE) and benzene. For these three compounds, carbon CSIA (and chlorine CSIA for the two halocarbons) achieves a reporting limit better than 1 ng/L using the full 100 L air sample volume. At this point, KEI does not recommend routine applications to other VOCs at equally low concentrations, due to significant cost of validation of the sampling methodology for additional target compounds. We invite inquiries about the feasibility of analysis of other VOCs occurring at tens of ng/L (contact the lab for availability of service).
The original report from the validation study:
McHugh, T., T. Kuder, M. Klisch, and R.P. Philp. 2012. Laboratory Validation Report: Use of Compound Specific Stable Isotope Analysis to Distinguish Between Vapor Intrusion and Indoor Sources of VOCs. ESTCP Project ER-201025, Laboratory Study Report, Version 2. January 2012. Prepared by GSI Environmental and University of Oklahoma for the Environmental Security Technology Certification Program (ESTCP).
Download the ER-201025 validation report →
Sample requirements:
The canonical approach to analysis of low ng/L samples relies on the use of the validated adsorbent medium (Graphsphere 2016, a rebranded Carboxen 1016 product) and specified range of air flow rates (the canisters must be provided by the client, e.g., rented from a third-party environmental lab). Other sampling methods with peer-reviewed validation may be accepted on a case-by-case basis, provided they are appropriate for the sample's actual concentration range. KEI will typically require at least two adsorbent tubes from each monitoring point (or a multiple of two if there are more than one target contaminant). Rapid shipping and refrigeration are recommended for this type of samples.
R&D in progress:
Ongoing in-house project aims to test an alternative preconcentration method based on passive adsorbent samplers. If successful, the new method will be integrated into the service portfolio.