title: A paper-based platform with a pencil-drawn dual amperometric detector for the rapid quantification of ortho-diphenols in extravirgin olive oil.
abstract: A simple, sensitive and fast responding device is described for the discrimination of hydrophilic ortho-diphenols, whose presence in abundant enough amounts is typical for extra virgin olive oils (EVOOs), from hydrophilic mono-phenols instead present in almost all vegetable oils. It consists of a dual electrode detector pencil-drawn at the end of a paper microfluidic channel, defined by hydrophobic barriers, where samples of these antioxidants, extracted from vegetable oils by a 80:20% v/v acetonitrile/water mixture, were applied. Thin-layer chromatographic runs conducted by using a 0.01 M H2SO4+ 1 M KCl running buffer allowed the selective detection of hydrophilic ortho-diphenols by profiting from the fact that they undergo reversible oxidation at less positive potentials than those required by monophenols for displaying their irreversible anodic process. On this basis, a potential for the oxidation of hydrophilic ortho-diphenols was applied to the upstream pencil-drawn electrode (W1) (at which a minor fraction of mono-phenols was also oxidized), while a potential for the reverse process involving the sole product (ortho-quinones) of the reversible oxidation of ortho-diphenols was imposed at the downstream pencil-drawn working electrode (W2). Thus, cathodic peak currents linearly dependent on analyte concentrations could be recorded at W2which led to a satisfactory detection limit (8 μM, equivalent to 1.23 mg/L) even when working electrodes W1and W2with same dimensions were employed. Improved sensitivities and lower detection limits were achieved by increasing the dimensions of W2with respect to W1, thanks to the improvement of the collection efficiency. Throughout this investigation, hydroxytyrosol (HTy) and tyrosol (Ty) were adopted as models of ortho-diphenols and mono-phenols, respectively, in view of their abundant presence in EVOOs. Real samples of EVOO from different production companies, of a simple olive oil and of a sunflower oil were analyzed. Different hydrophilic ortho-diphenol contents were found in EVOO samples (up to 40.8 mg/kg), while only a negligible amount turned out to be present in simple olive oil. No trace of these antioxidants were instead found in sunflower oil, as expected. All concentrations found were in good agreement with those detected by a more frequently employed spectrophotometric method used for the sake of comparison.
authors.affiliation: Department of Agrifood, Environmental and Animal Science, University of Udine, Via Cotonificio 108, I-33100, Udine, Italy. Electronic address: nicolo.dossi@uniud.it.
authors.forename: Nicolò
authors.initials: N
authors.lastname: Dossi
authors.affiliation: Department of Agrifood, Environmental and Animal Science, University of Udine, Via Cotonificio 108, I-33100, Udine, Italy.
authors.forename: Rosanna
authors.initials: R
authors.lastname: Toniolo
authors.affiliation: Department of Agrifood, Environmental and Animal Science, University of Udine, Via Cotonificio 108, I-33100, Udine, Italy.
authors.forename: Flavia
authors.initials: F
authors.lastname: Impellizzieri
authors.affiliation: Department of Agrifood, Environmental and Animal Science, University of Udine, Via Cotonificio 108, I-33100, Udine, Italy.
authors.forename: Franco
authors.initials: F
authors.lastname: Tubaro
authors.affiliation: Department of Agrifood, Environmental and Animal Science, University of Udine, Via Cotonificio 108, I-33100, Udine, Italy.
authors.forename: Gino
authors.initials: G
authors.lastname: Bontempelli
authors.affiliation: Department of Chemical and Geological Science, University of Modena and Reggio Emilia, Via Campi 183, I-41125, Modena, Italy.
authors.forename: Fabio
authors.initials: F
authors.lastname: Terzi
authors.affiliation: Department of Chemistry, Federal University of Minas Gerais, 31270-901, Belo Horizonte, Brazil.
authors.forename: Evandro
authors.initials: E
authors.lastname: Piccin
mesh_terms: D000975:Antioxidants / Q000032:analysis*; D002855:Chromatography, Thin Layer; D004566:Electrodes; D000069463:Olive Oil / Q000032:analysis*; D010084:Oxidation-Reduction; D010636:Phenols / Q000032:analysis*
chemical_list: D000975:Antioxidants; D000069463:Olive Oil; D010636:Phenols
keywords: Dual amperometric detection; Electrochemical detection of ortho-diphenols in oil samples; Extra virgin olive oil; Paper-based electrochemical devices (PEDs); Pencil-drawn electrodes (PDEs)