Validation of a microwave-assisted micellar extraction method for the oxibendazole determination in soil samples

Oxibendazole is a veterinary drug used as an antihelmintic for companion and farm animals. This drug may enter into the environment directly, via excretion of faeces and urine by grazing animals, or indirectly, when manure of treated farm animals are used as soil organic amendment. In this work, a simple, fast, reliable and sensitive method based on microwave-assisted micellar extraction (MAME) procedure, using Genapol X-080 (0.5%) as surfactant, has been developed for the quantification of oxibendazole in soil samples. Two classical methods, based on mechanical shaking and ultrasonic assisted extraction followed by solid phase extraction, were compared with the MAME procedure. Oxibendazole was determined by high-performance liquid chromatography (HPLC) with fluorescence detector. In the optimization of the MAME procedure were evaluated four parameters: surfactant volume, stirring, irradiation power and extraction time. Optimum conditions were 20 ml of Genapol X-080 (0.5%), irradiation power of 1000 W, extraction time of 2 minutes and stirring. At these MAME conditions, good recoveries (around 90%) were obtained, significantly higher than those found by classical method (below 55%). Two different soils from Madrid (central Spain) were included in the study. Results confirmed the extraction effectiveness is strongly influenced by physico-chemical soil properties.