Determination of inorganic anions in commercial seed oils and in virgin olive oils produced from de-stoned olives and traditional extraction methods, using suppressed ion exchange chromatography (IEC)

Ion exchange chromatography (IEC) with a conductivity detector and chemical suppression, was used to evaluate the content of some inorganic anions ( F - , Cl - , Br - , NO 2 - , NO 3 - , PO 4 3 - , SO 4 2 - and I - ) in commercial seed oils and in Sicilian virgin olive oil samples produced both from whole and de-stoned olives. Anions separation was achieved with a Metrosep Anion Dual 1 column (3.0 × 150 mm; 10.0 μm) packed with quaternary ammonium polymethacrylate. The isocratic elution was carried out using a solution of carbonate (3.12 mM)/hydrogen carbonate (3.25 mM)/2% acetone. Anions were extracted from the oily matrix using hot water pH 8 with carbonate/hydrogen carbonate buffer in an ultrasound bath. Under these conditions, detection limits ranging from 8.4 to 31 μg kg−1 (ppb) were achieved for all the studied anions; the precision of the method was within 6.5 rsd%. The analysis of vegetable oils provided evidence that the concentrations of bromide, nitrite, nitrate and iodide were lower than the detection limits in all the studied samples, whereas chlorides were the most abundant inorganic anions. Furthermore, the concentration of anions was significantly higher in olive oils obtained from the whole fruits than in samples produced from de-stoned olives.