# Plate Theory and Extensions - Retention Measurements on Close Eluting Peaks > Page 44

and,
_{ }(41)

Equation (41) is the Gaussian form of the elution curve equation and can be used as an alternative to the Poisson form in all applications of the Plate Theory.

# Retention Measurements on Close Eluting Peaks

The retention
data, are the most important measurements made in any chromatographic analysis.
In addition to providing data for identification (using the capacity ratio or
the separation ratio), retention times are also important in column design. It
will be shown later that the column efficiency needed to ensure resolution of a
pair of solutes can be calculated from the capacity ratio and the separation
ratio of the two peaks. However, when the solutes are eluted close together,
serious errors can arise in retention measurements. In addition, the error
becomes particularly significant when the accurate calculation of the required
retention and efficiency is particularly essential. The proximity of one peak
to another distorts the apparent positions of the peak maxima in the combined
envelope. Consequently, the *apparent* positions of the peak maxima are
significantly different from their *true* positions when eluted
individually. This effect is shown in Figure 10. The profiles of each peak are
calculated employing the normal Error function (Gaussian) and are then
superimposed by addition to provide the composite envelope.