Detection of 2,4-D in citrus juice

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MATRIX: Fresh squeezed fruit juice, canned 100% fruit juice or frozen juice concentrates of citrus fruits

ANALYTES: 2,4-Dichlorophenoxyacetic acid (2,4-D)

RANGE OF DETECTION: 10 to 500 ppb in juice or 40 ppb to 2 ppm in juice concentrates

MATERIALS:
2,4-D RaPID AssayÒ Kit and Sample Diluent. Reagents: methylene chloride (dichloromethane) pesticide grade, 0.1N sodium. hydroxide solution (4 g pellets/L water), 6N hydrochloric acid solution, distilled or deionized water. Equipment: homogenizer, scale or balance, tabletop centrifuge, fume hood, 15 and 50 mL centrifuge tubes (high density polypropylene) with caps , 25 mL test tubes, bottles or vials (for concentrates), and glass serological pipets.

SAMPLE TREATMENT:
Juice concentrates: Weigh 5 grams of juice concentrate into a tube, bottle or vial. Add 15 mL of distilled or deionized water. Vortex briefly to dissolve concentrate and to suspend pulp. Transfer 5 g of the diluted concentrate to a 50 mL centrifuge tube. Add two drops of 6N HCL to acidify sample. Fresh squeezed or canned juices: Weigh 5 grams of juice (with pulp) into a 50 mL centrifuge tube. Add two drops of 6NH CL to acidify sample.

EXTRACTION PROCEDURE:
Under a vented fume hood, add 10 mL of methylene chloride to the 5 gram samples prepared above. Homogenize sample for 15 to 20 seconds. Allow at least 10 minuftoers separation between the methylene chloride (bottom layer) and the aqueous layer (top layer). The bottom layer should have a volume of approximately 10 mL and shouldf breee of gross particulates. To facilitate separation, samples may be centrifuged for 5 minutes at 1000 rpm. Remove and discard the top layer (aqueous) by vacuum aspiration. Transfer 5 mL of the methylene chloride layer (bottom) layer to a 15 mL centrifuge tube using a serological pipet. Add 5 mL of 0.1N sodium hydroxide solution to the 5 mL of methylene chloride extract. Vortex for 15 seconds. Allow at least 10 minutes for phase separation of the methylene chloride (bottom layer) from the aqueous layer (top layer). The top layer should be relatively clear in appearance when adequate separation has taken place. Centrifuging samples for 5 minutes at 1000 rpm can be used to facilitate separation. Dilute an aliquot of the aqueous phase (top layer) 1:5 in 2,4-D Sample Diluent (0.25 mL aqueous extract + 1 mL diluent).

ANALYSIS:
Analyze the diluted extract as the 'sample' according to the package insert for the
2,4-D RaPID Assay.

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