title: Development and validation of a reversed-phase ion-pair liquid chromatography method for the determination of magnesium ascorbyl phosphate and melatonin in cosmetic creams.
abstract: A reversed-phase ion-pair high-performance liquid chromatographic method was developed and validated for the determination of magnesium ascorbyl phosphate and melatonin in cosmetic creams. The determination was performed on a BDS C 18 analytical column (250 x 4.6 mm i.d., 5 microm particle size); the mobile phase consisted of 0.020 M tetrabutylammonium hydroxide and 0.025 M potassium dihydrogen phosphate (pH 6.8) mixed with acetonitrile in a ratio (77:23, v/v) and pumped at a flow rate 1.00 ml min(-1). The UV detector was operated at 260 nm. The retention times of the magnesium ascorbyl phosphate, melatonin and chlorthalidone that was used as internal standard, were 6.55, 9.18 and 11.07 min, respectively. Calibration graphs are linear (r better than 0.9990, n=6), in concentration range 1.00-10.00 microg ml(-1) for magnesium ascorbyl phosphate and 0.63-6.25 microg ml(-1) for melatonin. The intra- and inter-day R.S.D. values were less than 6.0%, while the relative percentage error E(r) was less than 3.5% (n=5). The quantitation limits were 0.69 and 0.47 microg ml(-1), for magnesium ascorbyl phosphate and melatonin, respectively. The method was applied to the analysis of a cosmetic cream and proved to be suitable for rapid and reliable quality control.
authors.affiliation: University of Athens, School of Pharmacy, Department of Pharmaceutical Chemistry, 157 71 Panepistimiopolis, Zografou, Athens, Greece.
authors.forename: Athanasia
authors.initials: A
authors.lastname: Varvaresou
authors.forename: Efthimios
authors.initials: E
authors.lastname: Tsirivas
authors.forename: Kritonas
authors.initials: K
authors.lastname: Iakovou
authors.forename: Evagelos
authors.initials: E
authors.lastname: Gikas
authors.forename: Zaxarias
authors.initials: Z
authors.lastname: Papathomas
authors.forename: Ariadni
authors.initials: A
authors.lastname: Vonaparti
authors.forename: Irene
authors.initials: I
authors.lastname: Panderi