title: An evaluation of cis- and trans-retinol contents in juices using dispersive liquid-liquid microextraction coupled to liquid chromatography with fluorimetric detection.
abstract: This study describes a method for coupling dispersive liquid-liquid microextraction (DLLME) and normal-phase liquid chromatography (NP-LC) with fluorescence detection for vitamin A determination with the view to developing a new green sample preparation technique. Parameters affecting DLLME, including the nature and volume of both extractant and disperser solvents, salt addition and time and speed of the centrifugation step, were optimized. The sample was saponified according to European Standards to convert all forms of vitamin A to retinol. For microextraction, 8 mL water were placed in a glass tube with conical bottom and the saponified sample consisting of 2 mL of the methanolic extract containing 100 μL tetrachloroethane was rapidly injected by syringe, thereby forming a cloudy solution. Phase separation was performed by centrifugation, and a volume of 20 μL of the sedimented phase was analyzed by NP-LC. The enrichment factor, calculated as the ratio between the slopes of DLLME-LC and direct LC, was 50 ± 3. The matrix effect was evaluated for different juice samples, and it was concluded that sample quantification can be carried out by aqueous calibration when the standards are also submitted to saponification. The proposed method was applied for determining both cis- and trans-retinol isomers in commercial juices of different types. The intraday and interday precisions were lower than 6% in terms of relative standard deviation. The method was validated using two certified reference materials.
authors.affiliation: Department of Analytical Chemistry, Faculty of Chemistry, Regional Campus of International Excellence Campus Mare Nostrum, University of Murcia, E-30071 Murcia, Spain.
authors.forename: Pilar
authors.initials: P
authors.lastname: Viñas
authors.forename: María
authors.initials: M
authors.lastname: Bravo-Bravo
authors.forename: Ignacio
authors.initials: I
authors.lastname: López-García
authors.forename: Manuel
authors.initials: M
authors.lastname: Hernández-Córdoba
mesh_terms: D002853:Chromatography, Liquid; D005470:Fluorometry; D005638:Fruit / Q000737:chemistry*; D059627:Liquid Phase Microextraction; D013237:Stereoisomerism; D014801:Vitamin A / Q000032:analysis* / Q000737:chemistry
chemical_list: D014801:Vitamin A