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Abstract

Compound-specific isotope analysis using gas chromatography interfaced to isotope ratio mass spectrometry (GC/IRMS) was applied for the determination of delta C-13 values of the marine halogenated natural product 2,3,3',4,4',5,5'-heptachloro-1'-methyl-1,2'(.)bipyrrole (Q1) The delta C-13 value of a labmade Q1 standard (-34.20 +/- 0.27 parts per thousand) was depleted in C-13 by more than 11 parts per thousand relative to the residues of Q1 in dolphin blubber from Australia and skua liver from Antarctica. This clarified that the synthesized Q1 was not the source for Q1 in the biota samples. However, two Australian marine mammals showed a large variation in the delta C-13 value, which, in our experience, was implausible. Since the GC/IRMS system was connected to a conventional ion trap mass spectrometer by a post-column splitter, we were able to closely inspect the peak purity of Q1 in the respective samples. While the mass spectra of Q1 did not indicate any impurity, a fronting peak of PCB 101 was identified in one sample. This interference falsified the delta C-13 value of the respective sample. Once this sample was excluded, we found that the delta C-13 values of the remaining samples, i.e. liver of Antarctic brown skua (-21.47 +/- 1.47 parts per thousand) and blubber of Australian melon-headed whale (-22.80 +/- 0.33 parts per thousand), were in the same order. The standard deviation for Q1 was larger in the skua samples than in the standard and the whale blubber sample. This was due to lower amounts of skua sample available. It remained unclear if the Q1 residues originate from the same producer and location. Copyright (c) 2006 John Wiley & Sons, Ltd.