Experimental design for the rapid selection of separation conditions for methyl and propyl parahydroxybenzoate, phenylephrine hydrochloride and chlorphenamine maleate by ion-pair liquid chromatography, De Beer, J., Vandenbroucke C.V., and Massart D.L. , J.Pharm.Biomed.Anal., 0/11/1994, Volume 12, Issue 11, Number 1396, p.1379 - 1396, (1994)