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 C-18 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. (c) 2005 Elsevier B.V. All rights reserved.