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Based on 2H/1H measurements of commercial synthetic and natural citral (neral and geranial), on-line gas chromatography–pyrolysis–isotope ratio mass spectrometry (HRGC–P–IRMS) was used to determine the δ2HSMOW values of citral in essential oils from Cymbopogon flexuosus and C. citratus, Litsea cubeba, Lippia citriodora, Melissa officinalis and the Citrus species C. aurantium, C. limon, C. sinensis,C. paradisi and C. aurantifolia. The technique allowed reliable differentiation of natural (δ2HSMOW from −236 to −314‰) from synthetic products (δ2HSMOW from +38 to −197‰), even when some samples can also have very negative δ2H values, e.g. −197‰, but permitted no distinction within the origins from the various plant species. Copyright © 2001 John Wiley & Sons, Ltd. |