Analytical and Bioanalytical Chemistry

, Volume 397, Issue 7, pp 2807–2816 | Cite as

The isotopic mass defect: a tool for limiting molecular formulas by accurate mass

  • E. Michael ThurmanEmail author
  • Imma Ferrer
Original Paper


This paper describes the use of the relative isotopic mass defect, which is the mass defect between the monoisotopic mass of an element and the mass of its A + 1 or its A + 2 isotopic cluster. The relative isotopic mass defect is combined with the intensity of the isotopic cluster and a formula generator to find the correct molecular formula for unknown pesticides, using accurate mass measurements. This paper introduces the concept of the relative mass defect of isotopes and the isotopic mass average (IMA), especially for C, H, N, O, S, Cl, and Br, and how to correlate these measurements to the correct molecular formula of an unknown compound. A heuristic rule of ±3 × 10−3 u (+3 millimass units) is developed as a simple observational tool for viewing accurate mass data with four-decimal-place mass accuracy. This heuristic rule allows one to rapidly scan data “by eye” without the use of sophisticated software, and is a useful and rapid way of examining a molecular formula.


Liquid chromatography/mass spectrometry Accurate mass Mass defect Isotopologs Pesticides Unknown identification 



The authors acknowledge Agilent Technologies for instrument support and supplies and technical input on this paper. In particular, we acknowledge the help and assistance of Jerry Zweigenbaum of Agilent Technologies.


  1. 1.
    Thurman EM, Ferrer I, Fernandez-Alba AR (2005) J Chromatogr A 1067:127CrossRefGoogle Scholar
  2. 2.
    Ferrer I, Fernandez-Alba AR, Zweigenbaum JA, Thurman EM (2006) Rapid Commun Mass Spectrom 20:3659CrossRefGoogle Scholar
  3. 3.
    Kaufmann A, Butcher P, Maden K, Widmer M (2007) Anal Chim Acta 586:13CrossRefGoogle Scholar
  4. 4.
    Thurman EM (2006) J Mass Spectrom 41:1287CrossRefGoogle Scholar
  5. 5.
    Grange AH, Sovocool GW (2008) Rapid Commun Mass Spectrom 22:2375CrossRefGoogle Scholar
  6. 6.
    Ibanez M, Sancho JV, Pozo OJ, Niessen W, Hernandez F (2005) Rapid Commun Mass Spectrom 19:169CrossRefGoogle Scholar
  7. 7.
    Integrated Publishing (2009) Binding energy.
  8. 8.
    Audi G (2006) Int J Mass Spectrom 251:85CrossRefGoogle Scholar
  9. 9.
    NIST (2009) Atomic weights and isotopic compositions for all elements.
  10. 10.
    Cameron AE, Wichers E (1962) J Am Chem Soc 84:4175CrossRefGoogle Scholar
  11. 11.
    Sparkman DO (2002) Mass spectrometry desk reference. Global Publishing, PittsburghGoogle Scholar
  12. 12.
    Ferrer I, Thurman EM (2005) Anal Chem 77:3394CrossRefGoogle Scholar
  13. 13.
    Smith RM, Busch KL (1999) Understanding mass spectra: a basic approach. Wiley, New YorkGoogle Scholar
  14. 14.
    Thurman EM, Ferrer I, Zweigenbaum JA (2006) Anal Chem 78:6703CrossRefGoogle Scholar
  15. 15.
    Ferrer I, Thurman EM (2009) Liquid chromatography time-of-flight mass spectrometry: principles, tools, and applications for accurate mass analysis. Wiley, HobokenCrossRefGoogle Scholar
  16. 16.
    Ferrer I, Thurman EM, Fernandez-Alba A (2005) Anal Chem 77:2818CrossRefGoogle Scholar

Copyright information

© Springer-Verlag 2010

Authors and Affiliations

  1. 1.Center for Environmental Mass Spectrometry Department of Civil, Environmental and Architectural EngineeringUniversity of ColoradoBoulderUSA

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