Chromatography

Chromatography parameters for characterizing two separate analytes

Resolution R.

$$\mathrm{R.}=\frac{2\left(t_{r_2}-t_{r_1}\right)}{w_{\text{1}}+w_{\text{2}}}=\frac{\mathrm{1,18}\left(t_{r_2}-t_{r_1}\right)}{w_{{\text{0,5}}_{\text{1}}}+w_{{\text{0,5}}_{\text{2}}}}\begin{array}{l}{\mathit{t}}_{\mathit{R.}}\text{- (gross) retention time}\\ w\text{- base peak width}\\ w_{\text{0,5}}\text{- Peak width at half height}\end{array}$$

• Measure of the system's ability to separate two analytes under the chosen chromatographic conditions.
• A resolution larger is sufficient $\mathrm{1,5}$ (at $\mathrm{1,5}$ only overlap 0.3% of the peak areas).

Selectivity factor (separation factor) α

$$\alpha =\frac{K_{\text{2}}}{K_{\text{1}}}=\frac{k_{\text{2}}^{\text{'}}}{k_{\text{1}}^{\text{'}}}\begin{array}{l}K\text{- partition coefficient}\\ k^{\text{'}}\text{- capacity coefficient}\end{array}$$

• Measure of the separability of two analytes.
• The greater the difference in the distribution coefficients, the easier it is to separate.
• Since the substance eluted later is always at the top in the quotient, the selectivity factor is always greater than one.
• Values ​​greater than 1 to 10 are optimal.