Detection of thiabendazole in grapefruit juice


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MATRIX: Grapefruit Juice

ANALYTE: Thiabendazole (TBZ)

RANGE OF DETECTION: 10 to 250 ppb

Benomyl/ Carbendazim RaPID AssayÒ Kit and Sample Diluent. TBZ Standards (0, 10, 50 and 250 ppb TBZ) prepared in Sample Diluent. Reagents: ethanol and ethyl acetate (pesticide grade), 2M ammonium chloride (53.5 g/L in water, pH 9.5, adjusted with 14.5N ammonium hydroxide), distilled or deionized water, anhydrous sodium sulfate. Equipment: homogenizer (Polytron Model PT-10-35, Omni 5000 or equivalent), vacuum aspirator apparatus, nitrogen gas and evaporating apparatus, 1.5 mL micro-centrifuge tubes and 50 mL conical polypropylene centrifuge tubes, centrifuge(s) capable of accepting both sizes of centrifuge tubes, glass test tubes, serological pipettes, micropipet (200 mL), vortex mixer, and scintillation vials.

Weigh 5 grams of juice into a 50 mL conical centrifuge tube. Add 5 mL of ethanol, 15 mL of the 2M ammonium chloride solution and 20 mL of ethyl acetate. Homogenize the mixture for 2 minutes at medium speed. Centrifuge the tube at 5000 x g for 3 minutes to facilitate phase separation. Transfer approximately 15 mL of the upper layer (ethyl acetate) to a scintillation vial containing 1 g of anhydrous sodium sulfate and vortex the vial for 5 seconds. Transfer 4 mL of the sodium sulfate treated extract to a glass test tube and evaporate to dryness under nitrogen gas. A warm water bath can be used to facilitate drying. Dissolve the extract residue in 1 mL of Sample Diluent. Transfer the sample to a 1.5 mL micro-centrifuge tube and centrifuge at 10,000 x g for 10 minutes to pellet insoluble materials from the sample.

Prepare TBZ Standards at the concentrations indicated above. Set up a TBZ standard curve according to the directions of the Benomyl/ Carbendazim RaPID Assay package insert. Analyze the supernatant of the final centrifuged sample as 'sample'. Avoid disturbing pellet when collecting sample from the supernatant. If particulates are present in the sample, repeat centrifugation. Note: A TBZ procedure must be installed on the RPA-I analyzer so the TBZ concentration units are applied correctly.

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