A series of solvents with an increasing degree of polarity, generally used to explain solvent strength in liquid-solid or adsorption chromatography. A nonpolar solvent such as pentane would be at one end of the scale; dichloromethane would be an intermediate solvent; a strongly polar solvent, such as water, would be at the other end of the scale. Thus, when developing a method or running a gradient, an eluotropic series is useful for selecting solvents.