Selection of Organic Modifier

On most columns pure water cannot be used as mobile phase. Therefore, mainly binary mixtures of water with an organic modifier are used. Particularly small organic molecules such as methanol, acetonitrile and tetrahydrofuran are well suited, since they do not disturb the water "structure" too much. Since plots of log k versus mobile phase composition are often not linear usingTHF and MeCN, MeOH is recommended as standard organic modifier [7-9, 10], Water molecules have a stronger hydrogen-donating ability than methanol, while they have a slightly stronger hydrogen-accepting ability than acetonitrile but slightly weaker than that of methanol [41].

A new approach is the use of micelles as organic component. Micelle/water partition coefficients (Pmw) measured with a HPLC system were recently proposed as a new hydrophobic index [42], Possible advantages need to be evaluated.

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