title: Quantitative determination of (-)-epicatechin in cider apple juices by (1)H NMR.
abstract: This paper reports a quantitative determination method of (-)-epicatechin in apple juices by measuring of its signal at 7.05 ppm in the (1)H NMR spectrum. It is a direct method that does not need any previous derivatization. 1,3,5-Benzenetricarboxylic acid was added to the juice as internal standard for the determination of the absolute concentration of (-)-epicatechin. Ascorbic acid was also added to avoid enzymatic oxidation of the phenolics and to adjust the pH at 2.74, since the chemical shift of some compounds varies with the pH. Standard addition method accomplished with the juices of two different varieties of apples gave recoveries between 95 and 109%. The precision of the method was tested for repeatability (n=5) and reproducibility (n=13) obtaining a coefficient of variation of 5.8 and 8.6%, respectively. Limit of detection, calculated from "3S(y/x)+intercept", is 24 mg l(-1).
authors.affiliation: Applied Chemistry Department, Faculty of Chemistry, University of the Basque Country, Manuel Lardizabal 3, 20018 Donostia-San Sebastián, Spain.
authors.forename: Iñaki
authors.initials: I
authors.lastname: Berregi
authors.forename: José Ignacio
authors.initials: JI
authors.lastname: Santos
authors.forename: Gloria
authors.initials: G
authors.lastname: Del Campo
authors.forename: José Ignacio
authors.initials: JI
authors.lastname: Miranda