In contrast to analytical HPLC, preparative HPLC separates and refines compounds following chemical synthesis or extraction from natural sources. In separating such compounds to a high degree of purity a preparative system consumes a lot of solvent. However, the purity requirement for the solvent is not as great as that for analytical applications thereby allowing the solvent to be purchased in bulk at a reasonable price.
A proven analytical method does not necessarily upscale successfully to preparative levels. In analytical HPLC it is small quantities of analyte that are being separated whereas the aim for the preparative method is to produce fractions of reasonably large quantities of product, usually further purified by evaporative drying. Thus, the eluant recipe should avoid the use of non-volatile salts, such as ion-pair reagents, substituting them for volatile additives such as formic, acetic, trifluoroacetic or heptafluorobutyric acids. Furthermore, eluants based mainly on volatile organic solvents, such as methanol and acetonitrile, should be preferred over aqueous rich formulations.