Determination of thiabendazole residues in citrus fruits using a Multicommuted fluorescence-based optosensor

In this work, a method based on the combination of a multi-commuted flow system and solid-surface fluorescence spectroscopy has been developed and validated for the determination of thiabendazole residues in citrus fruits. The flow system was designed using three-way solenoid valves, controlled by Java-written home-made software, for independent automated manipulation of solutions. The native fluorescence signal of thiabendazole (using C18 as solid support) was used for its quantitation in citrus extracts. The sample treatment involved a liquid–liquid extraction with acetonitrile followed by a clean-up step using primary–secondary amine. Using an optimized sampling time, the analytical signal showed linearity in the range 0.3–10 mg kg−1 with a detection limit of 0.09 mg kg−1 and obtaining R.S.D. (%) values better than 2% for both lemon and orange matrices. Recovery experiments accomplished on different citrus fruit samples at different concentrations yielded recoveries between 87.1 and 108.9%. The proposed method was satisfactorily applied to the analysis of thiabendazole in different citrus samples, obtaining remarkably good agreement with liquid chromatography–electrospray/mass spectrometry reference method.