Development and validation of new methods for the determination of melatonin and its oxidative metabolites by high performance liquid chromatography and capillary electrophoresis, using multivariate optimization - Hevia, D.; Botas, C.; Sainz, R.M.; Quiros, I.; Blanco, D.; Tan, D.X.; Gomez-Cordoves, C.; Mayo, J.C. (Journal of Chromatography A, 2010)