Determination of 87Sr/86Sr isotopic ratio in olive oil and pomace using multicollector-ICPMS: Analysis of pomace residues as a simpler approach for determination of 87Sr/86Sr ratio in olive oil with low Sr content

This study presents an analytical procedure for measuring the 87Sr/86Sr isotopic ratio in olive oil and pomace using multicollector-inductively coupled mass spectrometry (MC-ICPMS). The developed method combines liquid-liquid extraction with an acid solution and degradation of organic residues in the extract by dry ashing and oxidation by H2O2 and HNO3. The method enabled 87Sr/86Sr ratios to be obtained in olive oil with Sr content as low as 0.2 ng g−1, with a precision of 54 ppm. The method’s validity was confirmed by an interlaboratory comparison using NIST SRM 2387, providing the first data on its elemental Sr (2380 ± 230 ng g−1; n = 10), and 87Sr/86Sr isotopic composition (0.70908 ± 0.00004; n = 14). The procedure was applied to olive oil and pomace samples, showing that they have an identical 87Sr/86Sr ratio, which was consistent with that determined in soils from the same orchards. The results thus revealed that Sr isotopic ratios of olive oil and pomace can both be used in geographical traceability studies of olive oil, which means that, instead of processing large volume of oil, characteristic 87Sr/86Sr signatures of olive oil can be more easily obtained by analyzing small quantities of pomace obtained by centrifuging the oil.