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Reconstructing bulk isotope ratios from compound-specific isotope ratios.

Douglas J Morrison1, Karen Cooper, Tom Preston

  • 1Stable Isotope Biochemistry Laboratory, SUERC, Rankine Avenue, Scottish Enterprise Technology Park, East Kilbride, Glasgow G75 0QF, UK. D.Morrison@suerc.gla.ac.uk

Rapid Communications in Mass Spectrometry : RCM
|May 26, 2010
PubMed
Summary

Bulk and compound-specific isotope analysis (CSIA) of fish oil showed excellent agreement for delta(13)C values. This validates CSIA as a reliable method for detailed carbon isotope studies in complex biological samples.

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Area of Science:

  • Environmental Science
  • Analytical Chemistry
  • Biogeochemistry

Background:

  • Bulk elemental analysis coupled with isotope ratio mass spectrometry is standard for delta(13)C analysis.
  • Compound-specific isotope analysis (CSIA) offers detailed isotopic information by analyzing individual compounds.
  • Theoretical concordance is expected between bulk and CSIA delta(13)C measurements.

Purpose of the Study:

  • To test the concordance between bulk and compound-specific isotope analysis (CSIA) for delta(13)C measurements.
  • To validate CSIA as a reliable method for complex biological matrices like fish oil.
  • To assess the agreement between bulk and reconstructed bulk delta(13)C values derived from CSIA.

Main Methods:

  • Fish oil samples were analyzed using bulk isotope analysis (isotope ratio mass spectrometry).
  • Fatty acids from saponified fish oil were converted to fatty acid methyl esters (FAMEs).
  • Compound-specific isotope analysis (CSIA) was performed using gas chromatography/combustion/isotope ratio mass spectrometry on FAMEs, with an internal standard for quantification.

Main Results:

  • Measured bulk mean delta(13)C was -23.75 ± 1.57 per thousand.
  • Reconstructed bulk mean delta(13)C from CSIA data was -23.76 ± 1.44 per thousand.
  • The Bland-Altman method showed good agreement between bulk and CSIA methods, with a mean difference of 0.01 per thousand and no significant bias.

Conclusions:

  • Bulk and CSIA methods for delta(13)C analysis of fish oil are in excellent agreement.
  • CSIA provides a reliable and accurate alternative for detailed carbon isotope investigations.
  • The findings support the use of CSIA for tracer studies and natural abundance analyses in complex organic samples.