Determination of etoxazole in the plum by gas chromatography-mass spectrometry

Abstract

Etoxazole is an acaricide (miticide/ovicide) belonging to the diphenyl-oxazoline group of chemicals and is suitable for use in integrated plant protection. Etoxazole is extremely selective. It has a permit to control red fruit spider, nettle mite and yellow vine spider. It is used in the formulation in the form of a concentrated suspension, where the amount of the active substance etoxazole is in a concentration of 110 g/L. Borneo (Agromarket, RS) formulation of etoxazole insecticide is better known for sale in Serbia. Etoxazole inhibits chitin biosynthesis during larval metabolism. It is used for fruits, primarily for apples, pears, apricots, peaches and plums. Analysis of pesticide residues in food and other environmental products have become an important factor in controlling the quality and safety of food and human health. The objective of this research is to provide information on the variation of etoxazole levels in the plums. A rapid and accurate method based on modified QuEChERS sample preparation was developed for determination of etoxazole in plums by gas chromatography-mass spectrometry (GC/MS). For the extraction, 10g of sample was weighed in a 50 mL PTFE centrifuge tube. Then, 10 mL of acetonitrile was added and the samples were shaken 3 min. Afterwards, 4 g of magnesium sulfate and 1 g of sodium chloride were added and the extract was then centrifuged for 5 min (4000rpm). In the second extraction phase, magnesium sulfate and PSA were used for clean-up. GC/MS analysis was performed using GC Clarus 680 PerkinElmer system equipped with a MS Clarus SQ8T mass spectrometer. The temperature of injector was 220°C, and sample injection was performed in splitless mode, and the injection volume was 1 μL. Matrix-matched solutions were also prepared by serially diluting the intermediate solution with blank etoxazole-free plum sample extracts to perform matrix-matched calibration. Matrix-compliant solutions were also prepared by serial dilution of intermediates with blind plum sample extracts to perform matrix-compliant calibration at the same concentrations as in the solvent. The linearity of the analytical response across the studied range of concentrations (0.01 - 0.10 mg/kg) was excellent, obtaining correlation coefficient higher of 0.999521. The average recovery for fortification levels of 0.01 and 0.1 mg/kg were 98.2% and 106.1% respectively. The precision values associated with the analytical method, expressed as RSD values, were less than 20%. Limit of quantification was 0.01 mg/kg. 20 plum samples were examined. Two samples of plums did not contain etoxazole, while the others contained in the amount of 0.044 to 0.061 mg/kg. The obtained value of the examined plums is above the MRL (maximum residue level) which is 0.04 mg/kg from the Commission Regulation (EU) 2018/686 of 4 May 2018 amending Annexes II and III to Regulation (EC) No 396/2005 of the European Parliament. The obtained validation data has confirmed that QuEChERS extraction ensures satisfactory results for determination etoxazole in plums. Such method showed the advantages of simplicity, rapidness, and sensitivity, and could meet the requirements for the determination of others pesticides residues in various fruits.