Optimization of Sensitivity

  • Kevin D. Altria
Part of the Methods in Molecular Biology book series (MIMB, volume 52)


The injection volumes involved in CE are very small (in the order of 1–10 nL). In addition, the area of capillary employed for on-column detection may be only 50 × 200 µm. Both these factors influence the detector sensitivity to a large extent. CE is less sensitive when directly compared to HPLC with typical injections of 10–50 µL and 1-cm detector cells. The difference may be up to an order of magnitude (2) when comparing at the same UV wavelength. Several strategies may be employed (Table 1) to maximize the sensitivity in CE. These include use of low UV wavelengths, increased capillary bore, and optimized sampling procedure.
Table 1

Summary of Approaches Available for Increasing Sensitivity

Action to improved sensivity

Drawback(s) to consider

Employ low-UV wavelength

Increased background noise—determine wavelength to give optimum signal-to-noise ratio

Increase capillary bore

Increased current, reduced EOF giving possible alteration in selectivity

Increased injection time

Reduction in separation efficiency; excessive time will result in run failure

Appropriate use of electrokinetic injection

Sampling bias for more mobile ions, sample matrix effects on injection amount

Increased electrolyte strength

Increased current and associated noise

Optimize electrolyte composition

Effects on selectivity and current

Decrease operating voltage

Increase in analysis time

Decrease temperature

Increase in analysis time

Capillary modifications

Reduction in separation efficiency and resolution, increased cost

Sample derivatization

Additional sampling handling

Indirect detection

Extra method development considerations

Wide-bore capillaries

EOF profile disturbed, adjustments to rinse and injection times, siphoning effects more pronounced

Increased detector slit width

Reduction in separation efficiency and resolution


Injection Time Indirect Detection Background Absorbance Hydrodynamic Injection Electrokinetic Injection 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.


  1. 1.
    Altria, K. D. (1993) Sensitivity optimisation for use of capillary electrophoresis in pharmaceutical analysis. LC-GC Int. 11, 438–442.Google Scholar
  2. 2.
    Hoffstetter-Kuhn, S., Paulus, A., Gassman, E., and Widmer, H. M. (1993) Influence of borate complexation on the electrophoretic behaviour of carbohydrates in capillary electrophoresis. Anal. Chem. 63, 1541–1547.CrossRefGoogle Scholar
  3. 3.
    Altria, K. D. (1993) Quantitative analysis of salbutamol related impurities by capillary electrophoresis. J. Chromatogr. 634, 323–328.CrossRefGoogle Scholar
  4. 4.
    Altria, K. D. (1993) Capillary electrophoresis for pharmaceutical research and development. LC-GC Int. 6, 616–620.Google Scholar
  5. 5.
    Chien, R. L. and Burghi, D. S. (1992) On-column sample concentration using field amplificatton in CZE. Anal. Chem. 64, 489A–496A.CrossRefGoogle Scholar
  6. 6.
    Jackson, P. E. and Haddad, P. (1993) Optimisation of injection technique in capillary electrophoresis for the determination of trace levels of anions in environmental samples. J. Chromatogr. 640, 481–487.CrossRefGoogle Scholar
  7. 7.
    Chervet, J. P., Van Soest, R. E. J., and Ursem, M. (1991) Z-shaped flow cell for UV detection in capillary electrophoresis. J. Chromatogr. 543, 439–449.CrossRefGoogle Scholar
  8. 8.
    Tsuda, T., Sweedler, J. V., and Zare, R. N. (1990) Rectangular capillaries for capillary zone electrophoresis. Anal. Chem. 62, 2149–2152.CrossRefGoogle Scholar
  9. 9.
    Swartz, M. E. and Merion, M. (1993) On-line sample preconcentration on a packed-inlet capillary for lmproving the sensitivity of capillary electrophoretic analysis of pharmaceuticals. J. Chromatogr. 632, 209–213.CrossRefGoogle Scholar
  10. 10.
    Amankwa, L. N., Albink, M., and Kuhr, W. G. (1992) Fluorescence detection in capillary electrophoresis. TRAC 11, 114–120.Google Scholar
  11. 11.
    Ruyers, H. and Van der Wal, S. J. (1994) Fully automated analysis of amino acid enantiomers by derivatisation and chiral separation on a capillary electrophoresis instrument. J. Liquid Chromatogr. 17, 1883–1897.CrossRefGoogle Scholar
  12. 12.
    Reinhold, N. J., Tjaden, U. R., and Vand der Greef, J. (1994) Automated on-capillary isotachophoretic reaction cell for fluorescence derivatisation of small sample volumes at low concentrations followed by capillary zone electrophoresis. J. Chromatogr. 673, 255–266.CrossRefGoogle Scholar
  13. 13.
    Motomizu, S., Oshima, M., Matsuda, S., Obata, Y., and Tanaka, H. (1992) Separation and determination of alkaline-earth metal ions as UV absorbing chelates with EDTA by capillary electrophoresis Determination of calcium and magnesium in water and serum samples. Anal. Sci. 8, 619–624.CrossRefGoogle Scholar
  14. 14.
    Wang, T. and Hartwick, R. A. (1992) Norse and detection limits of indirect absorption detection in capillary zone electrophoresis. J. Chromatogr. 607, 119–125.CrossRefGoogle Scholar
  15. 15.
    Foret, F., Fanali, S., Ossicini, L., and Bocek, P. (1989) Indirect photometric detection in capillary zone electrophoresis. J. Chromatogr. 470, 299–308.CrossRefGoogle Scholar
  16. 16.
    Vorndan, A. G., Oefner, P. J., Scherz, H., and Bonn, K. (1992) Indirect UV detection of carbohydrates in capillary zone electrophoresis. Chromatographia 33, 163–168.CrossRefGoogle Scholar
  17. 17.
    Nielen, M. W. F. (1991) Quantitative aspects of indirect UV detection in capillary zone electrophoresis. J. Chromatogr. 588, 321–326.CrossRefGoogle Scholar
  18. 18.
    Beck, W. and Engelhardt, H. (1992) Capillary electrophoresis of organic and inorganic cations with indirect UV detection. Chromatographia 33, 313–316.CrossRefGoogle Scholar
  19. 19.
    Tindall, G. W., Wilder, D. R., and Perry, R. L. (1993) Optimising dynamic range for the analysis of small ions by capillary zone electrophoresis. J. Chromatogr. 641, 163–167.CrossRefGoogle Scholar
  20. 20.
    Belder, D. and Schomburg, G. (1992) Enantiomer separation of tocainide analogues by cyclodextrin modified electrokinetic chromatography. JHRCC 15, 686–693.Google Scholar
  21. 21.
    Thomas, B. R., Fang, X. G., Chen, X., Tyrell, R. J., and Ghodbane, S. (1994) Validated micellar electrokinetic capillary chromatography method for the quality control of the drug substances hydrochlorothiazide and chlorothiazide. J. Chromatogr. 657, 383–394.CrossRefGoogle Scholar
  22. 22.
    Moring, S. E., Pairaud, C., Albin, M., Locke, S., Thibault, P., and Tindall, G. W. (1993) Enhancement of UV detection sensitivity for capillary electrophoresis. Am. Lab. July, 22.Google Scholar

Copyright information

© Humana Press Inc., Totowa, NJ 1996

Authors and Affiliations

  • Kevin D. Altria
    • 1
  1. 1.Glaxo Research and DevelopmentWare, HertfordshireUK

Personalised recommendations