31st EFFoST International Conference 2017

Trace heavy metals dangerous to human health, as Pb, As or Cu, can be present in olive oil because of contamination from soil and fertilizers, production or storage procedures, or exposition of the olive plants to vehicular and industrial emissions. The analysis of metal ions in such highly viscous organic matrix by using conventional analytical procedures is rather challenging since it requires the application of series of strong and time-consuming pretreatment steps which can be a source of contamination of the sample, possibly reflecting in scarce accuracy and precision. In this work we present a novel analytical approach that combines electrochemical preconcentration with spectroscopic analysis, focusing on the determination of lead in olive oil as a case study. In order to perform electrochemical experiments in such a complex and low-conductive food matrix, the room temperature ionic liquid (RTIL) [P14,6,6,6]+[NTf2]-, which is soluble in vegetable oils, was used as supporting electrolyte. For the development and validation of the analytical approach, at first, standard solutions of lead in non-aqueous medium were produced by an electrochemical procedure based on the galvanostatic anodic dissolution of high-purity Pb in RTIL. The analytical strategy developed here for the assessment of Pb content in oils can be summarized in the following steps: 1) mixing of the oil with the RTIL; 2) potentiostatic electrochemical metal deposition onto a thin Pt coil, directly from the tested real sample, 2 mL volume; 2) potentiostatic anodic stripping of the metal deposit after transfer to aqueous acid solution; 3) spectroscopic (ICP-MS or GF-AAS) analysis of the solution collected. The feasibility and performance of this analytical protocol were tested both in standard solutions of Pb(II) in RTIL, and in oil samples mixed with RTIL 0.5 M and spiked with Pb. Particular attention was devoted to the optimization of the potentiostatic deposition and re-oxidation parameters, by resorting to an experimental design model properly set up to get optimal conditions in terms of efficiency of deposition/stripping steps, quantitative recovery and measurement time. The proposed procedure was finally applied to the determination of Pb content in some Italian extra virgin olive oils. From the results obtained, it can be concluded that the combination of this simple and fast electrochemical preconcentration/stripping protocol followed by spectroscopic analytical quantification is a promising analytical strategy for the assessment of trace metal contaminants in edible oils, avoiding mineralization or other time-consuming pretreatments of the complex food matrix.