Solubility equilibrium gradients in the analytical ultracentrifuge: an approach towards the isolation of critical crystal nuclei in solution

  • Gordon Lucas
  • Lars Börger
  • Helmut Cölfen
Conference paper
Part of the Progress in Colloid and Polymer Science book series (PROGCOLLOID, volume 119)


Sedimentation equilibrium methods which are able to establish a solubility gradient for inorganic species in an ultracentrifugal field are presented. These methods are generally based on the concepts of density gradient and sedimentation equilibrium ultracentrifugation. However, in addition to the formation of a density or an equilibrium gradient, physicochemical parameters such as the pH or the solvent quality are varied throughout the solution column if appropriate high-density or high-molar-mass solutes are chosen or a mixture of solvents with different density is applied. This is demonstrated for two types of solubility gradients including for the case of a pH gradient; parameters for the adjustment of the overall pH are discussed. pH gradients were formed up to 3 pH units and are sensitive to addition of electrolytes, so they can only be applied to sparingly soluble salts. The gradual variation of the solubility of inorganic particles leads to the dissolution of the particles upon sedimentation when the dissolution point is reached. The ionic species formed show increased diffusion compared to the sedimenting particles, so they can diffuse back to regions of lower solubility and thus form a crystal again. This finally leads to an equilibrium situation for the critical crystal nucleus. In the case of a pH gradient with CdS, it is demonstrated that a transition from particles to dissolved ions indeed takes place and can be monitored in the analytical ultracentrifuge. For BaCrO4, the transition to the more soluble BaCr2O7 with decreasing pH can readily be monitored via the associated spectral changes, clearly demonstrating the possibility to perform chemical reactions in a pH gradient.

Key words

Sedimentation equilibrium Sedimentation velocity Density gradient ultracentrifugation Critical crystal nucleus 


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  1. 1.
    Gibbs JW (1961) The collected works of JW Gibbs. Yale University Press, New HavenGoogle Scholar
  2. 2.
    Kashchiev D (1982) J Chem Phys 76:5098CrossRefGoogle Scholar
  3. 3.
    Oxtoby DW, Kashchiev D (1994) J Chem Phys 100:7665CrossRefGoogle Scholar
  4. 4.
    Oxtoby DW (1998) Acc Chem Res 31:91CrossRefGoogle Scholar
  5. 5.
    Mutaftschiev B (1993) In: Hurle DTJ (ed) Handbook of crystal growth. Elsevier, Amsterdam, p 189Google Scholar
  6. 6.
    Yau ST, Vekilov PG (2000) Nature 406:494CrossRefGoogle Scholar
  7. 7.
    Oxtoby DW (2000) Nature 406:464CrossRefGoogle Scholar
  8. 8.
    Cölfen H, Pauck T (1997) Colloid Polym Sci 275:175CrossRefGoogle Scholar
  9. 9.
    Vossmeyer T, Katsikas L, Giersig M, Popovic IG, Diesner K, Chemseddine A, Eychmüller A, Weller H (1994) J Phys Chem 98:7665CrossRefGoogle Scholar
  10. 10.
    Hollemann AE, Wiberg N (1985) Lehrbuch der anorganischen Chemie, 91st edn. de Gruyter, New York, p 1042Google Scholar
  11. 11.
    Cölfen H, Pauck T, Antonietti M (1997) Progr Colloid Polym Sci 107:136CrossRefGoogle Scholar
  12. 12.
    Börger L, Cölfen H (1999) Progr Colloid Polym Sci 113:23CrossRefGoogle Scholar
  13. 13.
    Börger L, Cölfen H, Antonietti M (2000) Colloids Surf A 163:29CrossRefGoogle Scholar
  14. 14.
    Qi L, Cölfen H, Antonietti M (2000) Angew Chem Int Ed Engl 39:604CrossRefGoogle Scholar

Copyright information

© Springer-Verlag 2002

Authors and Affiliations

  • Gordon Lucas
    • 1
  • Lars Börger
    • 1
  • Helmut Cölfen
    • 1
  1. 1.Max Planck Institute of Colloids and InterfacesColloid ChemistryPotsdamGermany

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