[Determination of thiabendazole (TBZ) in grapefruit]

The officially recognized gas chromatographic method (detector: nitrogen-phosphorus detector) for determination of thiabendazole (TBZ) in grapefruits, tends to give results that are higher than the actual values. This may be due to the fact that more of the TBZ in authentic TBZ solution is adsorbed on the column than TBZ in the sample solutions that contain a lot of impurities. Because of this difficulty, two liquid chromatographic methods were compared. If a fluorescence detector is available, the method of Nakazato et al. (ethyl acetate extraction and ion pair HPLC) is the best for preparation of test solution. When an ultraviolet detector is used, clean-up of the ethyl acetate extract is necessary. By the method of Kitada et al., the retention time of TBZ becomes shorter after injection of many samples. In view of these results, the method of Nakazato et al. is the methods-of-choice for TBZ in grapefruit.