Refers to reversed-phase chromatography performed without water as a component of the eluent on a reversed-phase packing. Used for very nonpolar compounds that cannot be eluted or are difficult to elute from a reversed-phase column with 100% methanol or acetonitrile. In these cases, solvent A should be acetonitrile, and solvent B should be a stronger solvent such as tetrahydrofuran. Reversed-phase rules apply to nonaqueous reversed-phase chromatography; that is, the more nonpolar the analyte, the greater the retention.