For quantitative methods, the controlled immersion of the layer in a solution of the reagents is the preferred technique, since it does not rely on manual dexterity and produces superior results in scanning densitometry. Some solutions do not make good dip-ping solutions because they contain solvents that are too aggressive or viscous for convenient application (e.g., aqueous strong acids and bases). Dipping solutions are usually less concentrated than those used for spraying and water is often replaced by an alcohol for adequate permeation of reversed-phase layers. In general, it isnecessary to reformulate dipping solutions from earlier recipes for