A spectroscopic method which measures the difference in @A00028@ of left- and right-handed circularly polarised light by a material, as a function of the @W06659@. Most biological molecules, including @P04898@ and @N04245@, are @C01057@ and show circular @DT07357@ in their @UT07492@ absorption bands, which may be used as an indication of @S05530@. Metal centres that are bound to such molecules, even if they have no inherent @C01058@, usually exhibit CD in absorption bands associated with @L03518@-based or ligand-metal @C01008@. CD is frequently used in combination with absorption and @MT06778@ studies to assign electronic transitions.