Development and method validation for determination of Deltamethrin residue in olive oil using a reversed-phase high performance liquid chromatography

Abstract

Olive oil is the most important commodities produced in the Mediterranean region. Due to its significant economical importance, the usage of pesticides in its production is systematic, by using a wide range of plant protection products with a variety of modes of action. As a consequence, monitoring of their residue levels in these products is a necessity. In the present study a reversed-phase high performance liquid chromatography method, with a short sample preparation step, based on acetonitrile extraction is developed and validated in olive oil, with a large scope that includes Deltamethrin as pesticide. Good sensitivity and selectivity of the method were obtained with limits of quantification at 0.2 mg kg -1 . Deltamethrin has recovery rate which is of about 80℅. We confirm also the efficiency of alumina, used as adsorbent in the clean up step, to remove triglycerides and to get a pure extract. The agronomic implementation of this protocol allows us to determine the influence of some parameters on the dose and the period of treatment affecting the detected quantities of Deltamethrin residues in the produced olive oil. Indeed, we prove that the treatment dose should be specific for each case considering the olive variety, the geography of the orchard, and the predicted harvest time to determine the convenient dose of treatment. In addition, the results show that the preventive treatment at the blooming phase, does not lead to the concentration of Deltamethrin residues in the oil as it happens at the lipogenesis phase. Keywords: Clean up, Deltamethrin residues, HPLC, olive oil, dose of treatment I. Introduction Olive oil constitutes an essential ingredient in the Mediterranean meals, and more still, nowadays, we are discovering the multiple therapeutic virtues of this aliment thanks to its richness of antioxidants. Thus, producing countries are stimulated to enhance their export rate since it highly contributes in the national economy. Consequently, the use of agrochemicals and pesticides becomes compulsory to avoid the encountered production losses and in order to attain a higher quantity with a better quality. This issue is constantly subject to environmental debates. Indeed, these agricultural practices are responsible of potential risk for human health and can be a source of contamination for the soil, the micro-flora and the groundwater, leading to the entire ecosystem imbalance. With the emergence of the concept of sustainable development, organic food, and the expected decline of Maximum Residue Levels (MRLs) as those of baby-food, the producers are obliged to provide the external market with an olive oil containing pesticide quantities below the MRLs. These rigorous controls require pesticide residues extraction, purification and then analysis with accuracy. Many studies pointed out the difficulties in the separation of the pesticide molecules from fatty matrix that contains between 98 and 99 % of triglycerides (1), and worse still; the pesticide's components are concentrated in olive oil during the processes of its formation and extraction (2). Besides, the oil matrix protects them from any oxidation or degradation phenomena that lead to their persistence even at low levels. Therefore, a crucial clean up method is necessary for a precise separation of the pesticides from oil in order to avoid the co-elution of fats during chromatographic analysis. In fact, high molecular weight lipid (600- 1500) can cause damages on columns that may reduce the resolution's efficiency (3).