A method of chemical separation that involves passage of a liquid phase through a solid phase and relies on subtle chemical interactions to resolve complex mixtures into pure compounds. A small amount of the sample to be separated is injected onto the top of a column that is densely packed with spherical particles of small diameter, that is, the stationary phase. A liquid solvent, the mobile phase, flows through the column continuously to carry the sample from the top to the bottom of the column. During passage through the column, the components of the sample are transferred back and forth continuously between the two phases, and small thermodynamic differences in the chemical interactions of the various sample components with the mobile and stationary phases slow the passage of some solutes more than others and lead to their separation. The technique can be performed on very small scales for chemical analysis, dealing with micrograms or even nanograms of sample, or it can be performed on an industrial scale for purification of commercial products. The technique has great resolving power (see illus.).