Analysis of melatonin using a pH- and temperature-responsive aqueous chromatography system

A new method for the qualitative and quantitative analysis of an intracerebral hormone, such as melatonin, has been proposed, utilizing newly designed copolymers that include ion-exchange groups. These copolymers responded to both the temperature and the pH, and the copolymers were modified with cross-linked hydrogel applied onto aminopropyl silica beads. The products were evaluated as HPLC packing materials for a pH- and temperature-responsive chromatography. The property of the surface of the stationary phase was altered from hydrophilic to hydrophobic, and from charged to non-charged by changes in both the temperature and the pH. In the chromatographic system, we investigated how to change the retention of melatonin by varying the temperature. A pH- and temperature-responsive chromatography is expected to be useful for the separation of pharmaceuticals and biomolecules.