# Plate Theory and Extensions - Quantitative Analysis from Retention Measurements > Page 47

**Figure 13. Curves
Relating Apparent Separation Ratio Relative to Actual Separation Ratio for Two Closely
Eluting Peaks**

** **

In contrast, the separation ratio need only be in excess of about 1.035 on the high efficiency columns (10,000 theoretical plates), before accurate retention measurements can be made on the composite curve. It follows that,:

*Considerable care must be taken when accessing closely
eluting peaks. If the resolution is inadequate, measurements must be taken on
the individual solutes, chromatographed separately.*

# Quantitative Analysis from Retention Measurements

A consequence
of the above discussion on composite peak envelopes is that if the retention
times of a pair of solutes are accurately known, then the *measured retention
time* of the composite peak will be related to the *relative quantities*
of each solute present. It follows that an assay of the two components could be
obtained from accurate retention measurements only. This method of analysis was
shown to be feasible and practical by Scott and Reese (12).

Consider two solutes that are eluted so close together that a single composite peak is produced. Employing the Gaussian form of the elution equation, the concentration profile of such a peak can be described by the following equation: