AOAC Official Method 957
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1F90BA2B61C0474EBD16268858A89200 |
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日期： |
2024-7-30 |
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10.6.06,AOAC Official Method 957.14?,Captan Pesticide Residues,Spectrophotometric Method,First Action 1957,Final Action,Surplus 1994,(Applicable to firm fruits such as apples, pears, peaches, and plums,and to green vegetables.),A. Principle,Captan is extracted from crop with benzene; H2O, color, and appreciable,amounts of waxes are removed, and red color is developed,by fusion of captan with resorcinol at 135°C; color changes to yellow,on addition of CH3COOH.,B. Reagents,(a) Resorcinol.—Must be free of discoloration and pass following,tests: Fuse 0.5 g and dissolve in 25 mL CH3COOH. A at 425 nm,is ￡0.015, against CH3COOH. 1.00 g should not lose >2 mg in 4 h,overH2SO4; if more is lost, dry overH2SO4 until test is satisfactory.,(b) Cleanup mix.—10 parts Nuchar, 5 parts Hyflo Super-Cel, and,5 parts anhydrous Na2SO4.,(c) Captan standard solutions.—(1) Stock solution.—3 mg/mL.,Transfer 150 mg pure captan (available from Chevron Chemical,Co.,POBox 4010, Richmond,CA94804 USA) to 50mLvolumetric,flask and dilute to volume with benzene. (2) Intermediate solution.—,300 mg/mL. Pipet 10mLstock solution into 100mLvolumetric,flask and dilute to volume with benzene. (3) Working solution.—,30 mg/mL. Pipet 10 mL intermediate standard solution into,100 mL volumetric flask and dilute to volume with benzene.,C. Preparation of Test Portion,(a) Fruits.—Accurately weigh ca 500 g test portion into clean,dry jar with screw cap faced with sheet cork gasket covered with wet,filter paper, or other solvent-tight lid, and add 500mLbenzene. Multiples,of test portion-to-benzene ratio can be used. Agitate 15 min,drain benzene into container, and transfer to separator. (Transfer to,separator may be omitted where there is no separable aqueous layer.),Transfer ca 100 mL separated benzene layer to 250 mL,glass-stoppered flask, and decolorize and dehydrate with 3–4 g,cleanup mix, (b), by shaking vigorously ca 5 min. Filter through,folded paper, rejecting first 10–15 mL.,(b) Green vegetables.—Chop laboratory sample in food chopper,such as Hobart Food Cutter, mix, and transfer 100 g to explosion-,proof blender. Add 200 mL benzene and blend 2 min; add 20 g,anhydrous Na2SO4 and blend 2 min more. Pour mixture into 500 mL,centrifuge bottle, stopper with cork, and centrifuge at ca 1400 rpm,5–10 min. Decant benzene layer into 250 mL glass-stoppered,Erlenmeyer, add ca 6 g cleanup mix, (b)/100 mL benzene, and shake,vigorously ca 5 min. Filter through folded paper, discarding first,10 mL. If water–white solution does not result, repeat cleanup treatment.,Pipet 50 mL into 100 mL volumetric flask and dilute to volume,with benzene.,D. Determination,Pipet 5 mL filtrate, C(a), or aliquot, (b), into 25 ′200 mm test tube,and add 0.5 ± 0.1 g resorcinol. Heat 20 min in oil bath at 135 ± 5°C,cautiously at first to evaporate benzene; then immerse reaction tubes to,depth of ca 5 cmbut do not let them touch bottom of bath. Remove, and,immediately add 10–15 mL CH3COOH, followed by rapid immersion,in H2O at room temperature. Transfer quantity to 25 mL volumetric,flask, using CH3COOH, dilute to volume with CH3COOH, and mix.,Determine A at 425 nm in 1 cm cell against CH3COOH within 1 h.,Calculate ppm (mg/g) from standard curve.,E. Preparation of Standard Curve,Prepare standard curve simultaneously with test portions. Pipet 0,2, 4, and 5 mL aliquots of working standard solution into 25 ′,200 mm test tubes and add benzene to make total volume of 5 mL in,each tube. Add 0.5 ± 0.1 g resorcinol and continue as in determination,beginning “Heat 20 min in oil bath . . .”. (Note: One dropH2Oin,reaction tube will cause apparent loss of ca 20% captan. Do not leave,benzene aliquots in unstoppered reaction tubes where condensation,of moisture will take place.),References: JAOAC 40, 219(1957); 46, 143, 241(1963).,CAS-133-06-2 (captan),. 2000 AOAC INTERNATIONAL……
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