Optimization of an isocratic chromatogram using four solvents

5 OPTIMIZATION OF AN ISOCRATIC CHROMATOGRAM USING FOUR SOLVENTS 

Many separation problems require no gradient at all if the mobile phase is optimized. The disadvantage of all gradients is that they require reconditioning, which takes a certain amount of time. 

The best mixture (with respect to retention) for separating ten phenols by reversed-phase chromatography was found to be water-methanol (60 40), represented by chromatogram (J). The mobile phase polarity can be calculated as foUows  

P is then kept constant for all seven chromatograms. Chromatogram (2) with acetonitrile  

Compare with Section 10.3. The P values used here are different, namely Aieou = 2.6, Pacn = 3-2, 

Sections 9.4 and 10.3 have already provided the basis for optimization by attempting to work with three different solvent mixtures hexane-ether, hexane-dichloromethane and hexane-ethyl acatate for adsorption chromatography and water-methanol, water-acetonitrile, water-tetrahydrofuran for reversed-phase systems. However, this concept is not restricted to binary mixtures but a third or even a fourth component may be added in an attempt to improve the separation. An arrangement of seven different mixtures (Fig. 18.10) provides the best basis for systematic evaluation. An example is outlined below. 

Chromatogram with methanol and acetonitrile. The mobile phase is a 1 1 mixture of the eluents used in and . 

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