Optimized Pretreatment for Accurate Determination of Elemental Composition of Extra Virgin Olive Oil (EVOO) Using ICP-OES and ICP-MS: A Comprehensive Study

The goal of this study was to develop and validate an effective analytical method for the accurate quantification of trace elements—including Al, Fe, Zn, and rare earth elements—in extra virgin olive oils (EVOOs) using ICP-OES and HR-ICP-MS. Due to the low concentrations of these elements and the complex oil matrix, various sample pretreatment techniques were tested and evaluated using a certified reference material.

The optimized pretreatment involved agitation, sonication, and mineralization with nitric acid and hydrogen peroxide at room temperature. This approach was applied to 13 Italian EVOO samples to determine elemental profiles. Additionally, principal component analysis was used to investigate whether the elemental composition could differentiate oils based on their regional origin.

The original article

Optimized Pretreatment for Accurate Determination of Elemental Composition of Extra Virgin Olive Oil (EVOO) Using ICP-OES and ICP-MS: A Comprehensive Study

Paolo Inaudi, Ilenia Certomà, Mery Malandrino, Laura Favilli, Riccardo Cecire, Stefano Bertinetti, Ornella Abollino, Agnese Giacomino

Journal of Food Composition and Analysis, 2025, 107846

https://doi.org/10.1016/j.jfca.2025.107846

licensed under CC-BY 4.0

Selected sections from the article follow. Formats and hyperlinks were adapted from the original.

The elemental composition of foods holds significance in both nutritional and toxicological contexts, serving as a vital quality parameter (Abbatangelo et al., 2019, Acar, 2012, Inaudi et al., 2020). This is particularly true for extra-virgin olive oil (EVOO), where trace element concentrations play a crucial role in assessing its quality, storable period, and freshness (Wali et al., 2021). Derived from the fruits of the olive tree (Olea Europea. L), olive oil stands as a powerful source of vitamins and nutrients, making it a cornerstone of the Mediterranean diet, renowned not only for its distinct flavour but also for its potential health benefits (Bajoub et al., 2017, Bakkali et al., 2012).

In the context of olive oil quality assurance, the International Olive Council (IOC) has set forth stringent criteria, including maximum residue levels (MRL) for As, Cu, Pb (0.1 mg kg^-1), and Fe (3 mg kg ^-1) in both olive oils and olive-pomace oils (International Olive Council IOC 2019, n.d.). Additionally, regulatory standards, such as Codex Stan 33-1981, have established MRLs for Cu and Fe in various vegetable oils, ranging from 0.1 to 5 mg kg^-1 (Codex Stan 33-1981 2021, n.d.). This emphasis on quality control aligns with the recent surge in interest regarding element determination in EVOO samples, particularly for purposes of geographical traceability and authentication (Beltrán et al., 2015, Cecchi and Alfei, 2013, Giacomino et al., 2022). Against the backdrop of a global olive oil industry which saw production approaching 3 million tons between 2021 and 2022, with Europe contributing nearly 2 million tons (t) (including Spain, 1400 t; Italy, 329 t; Greece, 232 t; and Portugal, 206 t) and non-European countries contributing approximately 1 million tons (such as Tunisia, 240 t; Turkey, 235 t; Morocco, 200 t; Algeria, 91 t; Egypt, 20 t; and Argentina, 3 t), the need for robust quality assessment measures becomes ever more pressing (Chiaudani et al., 2023, International Olive Oil Council, n.d).

Despite being celebrated for its positive health impacts, olive oil, like other vegetable oils, can harbour pollutants, including toxic elements (Cabrera-Vique et al., 2012). These contaminants may stem from soil composition, environmental pollution, or contamination during production and storage processes. Thus, understanding and monitoring trace element levels in olive oil is imperative for ensuring its safety and nutritional integrity. On the other hand, among the factors influencing its quality and nutritional profile, the elemental composition and presence of rare earth elements (REEs) play significant roles, influencing both flavour and health attributes (Chiaudani et al., 2023, Gu et al., 2018).

In recent years, advancements in analytical techniques have enabled precise characterization of the elemental composition of EVOO (Jiang et al., 2015, Ma et al., 2025, Maléchaux et al., 2020, Rotondo et al., 2024).

Inductively Coupled Plasma Optical Emission Spectroscopy (ICP-OES) and Inductively Coupled Plasma Mass Spectrometry (ICP-MS) have emerged as powerful tools for elemental analysis due to their sensitivity and ability to detect trace elements (Angioni et al., 2006, Astolfi et al., 2021, Chiaudani et al., 2023, Cindric et al., 2007, Gaggero et al., 2020, Giacomino et al., 2022, Llorent-Martínez et al., 2011, Zeiner et al., 2005). These techniques offer insights into the concentration of essential minerals and potentially harmful elements, thereby informing quality control measures and ensuring consumer safety. Moreover, the direct connection between the soil composition and the elemental content in EVOO suggests the use of the element’s concentrations for the origin recognition of the products, useful in the fight against food frauds.

However, the accurate determination of elemental content in EVOO is contingent upon effective sample pretreatment procedures. Various factors such as matrix interference and sample complexity necessitate meticulous optimization of pretreatment conditions to minimize analytical errors and maximize sensitivity. In this study, we tested different procedure to identify the optimal pretreatment conditions for the analysis of EVOO samples.

Furthermore, the vast datasets generated by ICP-OES and ICP-MS demand sophisticated data analysis techniques to extract meaningful insights. Chemometric methods offer a robust framework for multivariate analysis, facilitating the interpretation of complex data matrices and uncovering hidden patterns within the elemental profiles of EVOO samples. By employing chemometric processing, we aim to unravel the intricate relationships between elemental composition, geographical origin, and processing methods, shedding light on the factors influencing the quality and authenticity of Italian EVOO.

In this paper, we present the results of our investigation, encompassing the optimization of pretreatment conditions for elemental analysis of EVOO using ICP-OES and ICP-MS, followed by chemometric treatment of the acquired data. Our findings contribute to the comprehensive understanding of the elemental composition and REE content of Italian EVOO, laying the groundwork for future studies aimed at enhancing its quality, nutritional value, and authenticity.

2. Material and methods

2.1. Instruments and reagents

Dissolution of samples took place in vessels made of polytetrafluoroethylene (PTFE) using the Milestone MLS-1200 Mega microwave laboratory unit (Milestone, Sorisole, Italy). Sample analyses were conducted using an Optima 7000 ICP-OES (Perkin Elmer, Norwalk, CT, USA) and a sector field ICP-MS Element 2 (HR-ICP-MS, Thermo Fisher Scientific, Waltham, Massachusetts, MA, USA). High purity water (HPW) from a Milli-Q apparatus (Millipore, Burlington, MA, USA) was utilized for sample preparation and standard solutions. Analytical grade reagents were employed consistently throughout the experiments, and standard metal solutions were prepared from 1000 mg L^-1 single element Merck Titrisol stock solutions (Merck, Darmstadt, Germany).

3. Results and Discussion

3.2. ICP-OES

Table 3 reports the results obtained for the samples of Italian EVOO analyzed using ICP-OES are reported, and represented in Fig. 1.

Journal of Food Composition and Analysis, 2025, 107846: Fig. 1. Distributions of major and minor element concentrations in the EVOO samples.

For all samples, in addition to the elements listed in the table, the determination of As, B, Ba, Cd, Cr, Cu, Mn, Ni, P, Pb, Si, Sn, Sr was also attempted, but their content was not quantified since they were present in concentrations below the detection limit. One essential and one probably essential micronutrient, recorded in low concentrations in almost all samples of EVOO, are Co and V, which probably derive from the natural soil composition. Regarding geogenic elements, Al is also likely derived from the natural soil composition; however, it is a toxic metal for plants. As seen in Table 3, concentrations vary within a narrow range of values. Among the essential and most important elements from a biochemical point of view, K stands out with concentrations above 1 mg kg^-1 in almost all samples except for EVOO8 and EVOO9, followed by Na with a minimum concentration (0.68 mg kg^-1) in EVOO4 and a maximum (1.76 mg kg^-1) in EVOO12, and Mg with a maximum concentration recorded as 0.71 mg kg^-1 in EVOO7. Also, Li and Se, as shown, fall among the elements with concentrations greater than or equal to 1 mg kg^-1. Lithium, a non-essential element, is found in traces in numerous plants that absorb it from the environment. Selenium, on the other hand, is a micronutrient naturally present in both animal and plant species. The marked Se enrichment in Sardinian oils aligns with the island’s basaltic–volcanic soils, while the Li‑ and Al‑rich Ligurian samples reflect granite‑derived coastal substrates. Finally, the presence of antimony, although in low concentrations in all samples of EVOO, cannot be neglected: antimony is a potentially toxic element with no biochemical relevance that can be found in traces in soils.

3.3. ICP-MS

ICP-MS was employed to determine several metals including Cu, Fe, Mn, Ni, Zn. Attention was focused onto these five trace metals because they have an influence on the flavour and oxidative stability of the oil due to their catalytic effect on the auto-oxidation mechanism. Moreover, the rare earth elements (Ce, Dy, Er, Eu, Gd, Ho, La, Lu, Nd, Pr, Sc, Sm, Tb, Tm, Y, Yb) have been detected due to their correlation with geogenic source. Analyses were conducted at both low and medium resolution. The results of minor elements (μg kg^-1) are reported in Table 4 and represent in Fig. 1. Rare Earth element’s concentrations are reported in Table S5 for metals (ng kg^-1).

Journal of Food Composition and Analysis, 2025, 107846: Table 4. Concentrations of 5 elements in Italian EVOOs obtained by ICP- MS. The results are expressed in µg kg-1.

It was not possible to obtain a satisfactory calibration curve for ⁵⁶Fe at low resolution due to interference from ⁴⁰Ar¹⁶O; therefore, this element was determined by considering the isotopes 54 and 56 at medium resolution. Additionally, the concentrations of Ni, Cu, and Zn were derived from the averages of their isotopes: 60 and 62 for nickel, 63 and 65 for copper, and 64, 66, and 68 for zinc. For rare earth elements, only concentrations above the instrumental detection limit are reported.

Iron is a micronutrient utilized by plants in chlorophyll formation; copper is also indispensable for plants as it plays a crucial role in photosynthesis, respiration, protein synthesis, and cell wall metabolism. Fe and Cu content in EVOOs can derive from the soil composition, from some fertilizers used in olive cultivation (copper salts), or from contamination during oil processing and storage. As seen in the table, both Cu and Fe exhibit significant variability in concentration values, ranging from approximately 10 to 117 µg kg^-1 and from 342 to 1217 µg kg^-1, respectively. The importance of these two metals for EVOO quality lies in their ability to act as pro-oxidants by catalyzing the autoxidation reactions of the oil itself. As for Zn, noticeable variability in concentrations can be observed; for example, the value of approximately 3055 µg kg^-1 in EVOO12 stands out compared to those samples where no zinc was detected. Considering that the median value is 246 µg kg^-1, a contamination in EVOO12, during analysis, cannot be ruled out. Calabrian EVOO 12‑13 show the highest suite of REEs, consistent with weathered granitoid soils common in that area. Zinc is an essential element in plants, which can absorb and accumulate it, as it serves as an activator for some enzymes. Periodic application of Bordeaux‑type copper fungicides and Zn/Mn‑containing foliar fertilisers plausibly explains the Cu peaks in EVOO7 and the Zn outlier in EVOO12. It is considered a pollutant when present in high concentrations; in EVOOs, its presence is deleterious as it is one of those metals that increase the speed of oil autooxidation reactions. The levels of Mn are lower than 20 µg kg^-1 in all samples; it can be hypothesized that they derive from soil composition rather than oil processing. Literature reports that its catalytic activity falls between that of Cu and Fe, and a Mn concentration near 0.6 mg kg^-1, much higher than the one found in this study, induces a 50% decrease in oil resistance to oxidative processes (Li et al., 2021). Finally, nickel was detected only in samples of EVOO12 and EVOO13, albeit in low concentration. Veneto orchards are partly irrigated with moderately saline groundwater from the Po‑delta alluvium, which can raise Na and Mn in the fruit. Manganese and iron uptake are enhanced during late‑season maturation; the oils collected in November (Veneto, Sardinia) therefore show higher Mn and Fe than early‑harvest Ligurian oils.

In general, the data obtained exhibit significantly high values of RSD% for the rare earth elements. It should be noted that pretreatment tests aimed at optimizing the analysis procedure was conducted by determining metals using ICP-OES, when the response of rare earth elements was not yet known. Furthermore, low concentrations could also be a potential cause of the high RSD% values obtained.

4. Conclusion

The conducted study enabled the development of a procedure for determining the element content within extra virgin olive oils. The homogenization of the samples before their mineralization was found to be of paramount importance to obtain repeatable concentrations. Chemometric treatment revealed the possibility of using them as markers for oil typification according to their origin. In the case of rare earth elements, however, the obtained results showed high variability, likely due to the low concentrations involved. Therefore, future developments will be dedicated to identifying optimal pretreatment conditions that allow for minimized variability in the rare earth element content across different aliquots of the same sample. Specifically, a specific experimental design will be conducted with the aim of enhancing the discriminatory capacity of the inorganic component toward the geographical origin of the sample.