Mass-spectrometer bias in stable isotope ecology

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  2. Dr Aileen Mill
  3. Dr Christopher Sweeting
  4. Carolyn Barnes
  5. Saoud Al-Habsi
  6. Michael MacNeil
Author(s)Mill AC, Sweeting CJ, Barnes C, Al-Habsi SH, MacNeil MA
Publication type Article
JournalLimnology and Oceanography: Methods
ISSN (print)1541-5856
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Stable isotope analysis (SIA) is recognized as a powerful analytical tool with numerous ecological applications. This has been highlighted by the increase in popularity of the isotope ratio mass spectrometry (IRMS) technique and the large number of studies reporting isotopic data. Comparisons of new isotopic data with previously published results and the use of large volumes of isotopic ratios in meta-analyses to explain isotopic variance are commonplace. Such data often originate from different IRMS instruments and are assumed to be readily comparable as all instruments are calibrated to International Atomic Energy Agency (IAEA) standards. To test the validity of this assumption, we analyzed a single ecological sample (homogenized cod muscle, Gadus morhua) on eight anonymous IRMS instruments and found significant variation in both delta N-15 and delta C-13. We used a one-way analysis of variance (ANOVA) with random effects to estimate the average variability of laboratory results within and among instruments. Overall, 74% of variation in d15N and 35% of variation in d13C of a single ecological sample was explained by differences in the IRMS instrument used. In light of these findings, researchers are encouraged to submit their own sample reference to provide an independent check on variation between runs and between instruments; consistent discrepancies between instruments should be corrected through linear regression. Comparisons of data obtained from multiple instruments should acknowledge inter-instrument variation as a potential source of error.
PublisherAmerican Society of Limnology and Oceanography
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