Determination of agrochemical multi-residues in grapes. Identification and confirmation by gas chromatography-mass spectrometry

The valley of the Sao Francisco river, northeastern Brazil, is home to the major mango and grape producers of Brazil, many of which already export to foreign markets. Grape cultivation in the Sao Francisco River Valley is arguably the most important fruit cultivation in the region. The products are assessed using stringent criteria through audits based on international standards, which specify the maximum levels of agrochemical residues in the fruits. The objective of this study was to adapt and validate the effective Quick, Easy, Cheap, Effective, Robust and Safe (QuEChERS) method for the determination of agrochemical multi-residues in grapes. Agrochemicals of interest included fungicides, insecticides, and herbicides, including groups of compounds such as pyrethroids, triazoles, dicarboximides, quinones, tetrazines, dinitroanilines, carbamates, organochlorine, and organophosphate. The grapes were collected weekly over a period of 6 months on farms and markets in the region (approximately 140 samples). Sample preparation involved ultra-turrax extraction, centrifugation and clean-up with a mixture of inorganic salts and polymers, enabling the identification and confirmation by gas chromatography-mass spectrometry (GC-MS) of 80 agrochemical multi-residues in grapes. The results showed QuEChERS to be an accurate and effective method, with detection limits (0.0025-0.02 mg kg(-1)) and quantification limits (0.01-0.22 mg kg(-1)) within the requirements of both domestic standards (Ministry of Agriculture) and international standards for food, including Codex Alimentarius and others. The repeatability was tested at intermediate levels of limits of quantification with seven replicates, presenting variation coefficients in the range 2.1-15%. Recovery percentages were satisfactory, and within the range 70-125%.