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To quantify the separation between two compounds, the resolution factor R is calculated from the chromatogram (Figure 1.8):

(1.33)

For two adjacent peaks, this relationship involves two parameters: firstly, the difference between their retention times, t_R(2) − t_R(1), which corresponds to the distance between the two peaks, and, secondly, their half‐width at the base, ½ (ω₂ + ω₁) if we assume that each peak corresponds to an isosceles triangle (Figure 1.8).

Other expressions derived from the preceding ones and established with a view to replacing one parameter by another or to accommodating simplifications may also be employed to express the resolution. Therefore, Eqs. (1.34)–(1.36) are used quite often.

Equation (1.35) shows how resolution is affected by the efficiency, capacity factor, and selectivity factor. The chromatograms in Figure 1.9 present an experimental verification of this.

(1.34)

(1.35)

(1.36)

Figure 1.8 Resolution factor. A simulation of chromatographic peaks by juxtaposition of two identical Gaussian curves to a greater or lesser extent. The visual aspects corresponding to the values of R are indicated on the diagrams. From a value of R = 1.5 the peaks can be considered to be baseline resolved, the valley between them being around 2%.