Chromedia Resolution Equation Tool

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  • Published: Apr 2, 2009
  • Channels: Ion Chromatography / Proteomics & Genomics / HPLC / Detectors / Sample Preparation / Laboratory Informatics / Separations Science Digest / Gas Chromatography / Electrophoresis
thumbnail image: Chromedia Resolution Equation Tool

Resolution Equation Tool

We have created this tool to help you intuitively understand the resolution factor.

Try it, it is free... and it is fun!

Frank van Geel, Chromedia

If we combine all of the equations concerning efficiency, selectivity, retention and resolution mathematically, then we obtain the so called "resolution equation":

Resolution Equation

in which: 

  • Rs = separation or resolution factor
  • alpha = selectivity factor
  • k = retention factor
  • Nth = theoretical plate number

With this equation we can explain and predict the effect of any change in the chromatographic parameters on the separation process. This equation is also the basis for method optimisation.

The tool should help you to intuitively understand the resolution factor. Slide the sliders to see how the three parameters alpha, k and Nth change the peaks. We hope that this will increase your intuition of how the parameters influence the resolution factor.

After having played with this tool, you should have a better understanding of the following guidelines:

  • The sample components must be retained by the stationary phase in order to become separated (k > 0).
  • Separation depends on different degrees of retention i.e. the k values must be different from each other so that the selectivity alpha is greater than unity. The greater the difference, the greater is the chance of separation.
  • The column plate number N must be high enough in order to produce sufficiently narrow peaks that are baseline-separated. When N is not sufficiently high, peaks will overlap and the separation will be incomplete.
  • A resolution value smaller than 1.5 leads to incomplete separation: the peaks overlap. The overlap can sometimes be so large that the individual components cannot be distinguished at all. One peak then "contains" two compounds. With a resolution value between 1.25 and 1.5, the extent of separation depends on peak symmetry. When Rs is smaller than 1.25 we can never obtain baseline separation.

You can further improve your understanding we have opened up Chromedia's chapter "Test your know-how"by Harold McNair.

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