Validation of a rapid and simple method for the preparation of aqueous organic compounds prior to compound specific isotope analysis |
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| Authors: | Timothy J Benbow Russell D Frew Alan R Hayman |
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| Institution: | bDepartment of Chemistry, University of Otago, P.O. Box 56, Dunedin, Otago 9081, New Zealand |
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| Abstract: | Landfill leachate comprises a complex mixture of contaminants many of which may have multiple sources in the environment confounding conventional techniques for apportioning sources. Compound specific isotope ratio mass spectrometry offers the potential to “fingerprint” compounds enabling discrimination to be made between different sources. This paper presents a rapid and highly reproducible method to prepare landfill leachate samples for compound specific isotope analysis. A suitable solid phase extraction (SPE) method was developed using artificial contaminant solutions, natural waters spiked with artificial contaminants (eucalyptol, dodecane, benzothiazole, dibutyl phthalate and naphthalene), and samples of landfill leachate. The elution of adsorbed compounds from the SPE cartridge was found to be the major cause of hydrogen and carbon isotope fractionation. Three different SPE cartridge types were tested: C18, Strata-X and ENV+. Fractionation of between 1‰ and 245‰ for hydrogen isotopes and 0–1.83‰ for carbon isotopes was observed. Part of the fractionation could be attributed to the different SPE cartridges but the major contribution was from the choice of the eluting solvent. Our results indicated hydroxylated styrene-divinylbenzene cartridges eluted with dichloromethane resulted in negligible hydrogen or carbon isotope fractionation for any of the tested organic compounds.The isotopic fractionation of hydrogen and/or carbon of most artificial contaminants were proportional to the efficiency with which they were extracted from water. Only naphthalene exhibited isotopic fractionation unrelated to its extraction efficiency but this fractionation was negligible.The comparative extraction of landfill leachate using SPE and LLE indicated SPE generally extracts slightly more of each compound from leachate than LLE. This relationship is stronger than for polar compounds. In addition, the δD composition of each compound prepared using SPE was with two standard deviations of the sample compound prepared using LLE, and the δ13C composition of each compound prepare using either method was mostly within two standard deviations. |
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