title: A novel electroanalytical approach based on the use of a room temperature ionic liquid for the determination of olive oil acidity.
abstract: In this paper, a novel voltammetric/amperometric approach for the direct determination of free acidity (FFA, expressed as mass percentage of free oleic acid) in olive oil samples is presented. The method is based on the reduction processes occurring at a platinum microdisk electrode involving the free fatty acids present in the matrices. To overcome problems related to the low conductivity of the samples investigated, olive oils were mixed with suitable amounts of the room temperature ionic liquid (RTIL), tri-hexyl(tetradecyl)phosphonium bis (trifluoromethylsulfonyl) imide ([P14,6,6,6]+[NTf2]-), which acted as a supporting electrolyte. Conditions for a reliable quantification of the acids were preliminarily investigated by performing voltammetric and chronoamperometric measurements in RTIL solutions containing oleic acid at different concentrations. Oleic acid (OA) was chosen as a model compound as it is the main component of the FFA content in olive oils. In order to establish the effect of oxygen on the electroanalytical responses, the reduction process of OA was investigated under both deoxygenated and oxygenated conditions. It was found that, in both situations, the current arising from the electrode process of OA depended linearly on the OA concentration over a wide range varying from 0.1% to 8% OA (w/w). This range includes FFA values which can be found on all categories of commercially available oil samples, including extra-virgin, virgin and lampante oils. Voltammetric and chronoamperometric experiments were also performed in oil/RTIL samples artificially acidified (extra-virgin olive oils with known addition of oleic acid) and in natural olive oils from some commercial categories. The results obtained indicated that the electrochemical procedure developed was satisfactory in terms of both sensitivity and detection limits. The reliability of the proposed approach for the detection of FFA was finally assessed by comparison of the voltammetric/chronoamperometric values with those obtained by the official method for quantification of olive oil acidity, which is an acid/base volumetric titration.
authors: Department of Molecular Science and Nanosystems, Ca' Foscari University of Venice, Campus Scientifico Via Torino 155, 30172 Venezia Mestre, Italy. Electronic address: toni@unive.it.
authors: M Antonietta
authors: MA
authors: Baldo
authors: Department of Pharmacy, University of Genoa, Viale Cembrano 4, 16148 Genova, Italy.
authors: Paolo
authors: P
authors: Oliveri
authors: Department of Pharmacy, University of Genoa, Viale Cembrano 4, 16148 Genova, Italy.
authors: Remo
authors: R
authors: Simonetti
authors: Department of Molecular Science and Nanosystems, Ca' Foscari University of Venice, Campus Scientifico Via Torino 155, 30172 Venezia Mestre, Italy.
authors: Salvatore
authors: S
authors: Daniele
mesh_terms: D055664:Electrochemical Techniques; D004566:Electrodes; D006046:Gold / Q000737:chemistry; D006863:Hydrogen-Ion Concentration; D007094:Imides / Q000737:chemistry*; D052578:Ionic Liquids / Q000737:chemistry*; D019301:Oleic Acid / Q000032:analysis* / Q000737:chemistry; D000069463:Olive Oil / Q000737:chemistry*; D010084:Oxidation-Reduction; D010984:Platinum / Q000737:chemistry; D013696:Temperature
chemical_list: D007094:Imides; D052578:Ionic Liquids; D000069463:Olive Oil; D019301:Oleic Acid; D010984:Platinum; D006046:Gold
keywords: Electroanalysis; Microdisk electrodes; Oleic acid; Olive oil acidity; Room temperature ionic liquid