AOAC Official Method 964
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35502087B4D044C4A2AAB8F3F37B54CE |
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0.02 |
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1 |
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日期： |
2024-7-30 |
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10.6.13,AOAC Official Method 964.19?,Dodine Pesticide Residues,Spectrophotometric Method,First Action 1964,Final Action 1965,Surplus 1994,(Applicable to apples, peaches, pears, pecans, and strawberries.),A. Reagents,(a) Bromocresol purple solution.—Recrystallize indicator-grade,bromocresol purple from boiling toluene (ca 2 g/100 mL). Dissolve,0.4 g recrystallized material in 75 mL 0.01M NaOH; if necessary,add additional 0.01M NaOH to bring pH to 6.0–6.1. Filter, if necessary,and dilute to 500mLwithCO2-freeH2O. Store in brown bottle.,(b) Buffer solution.—pH 5.5. Dissolve 15.2 g Na2HPO4×7H2O,and 74.0 g NaH2PO4×H2O in CO2-free H2O and dilute to 1 L.,(c) Dodine (DDGA) standard solutions.—(1) Stock solution.—,130 mg/mL. Dissolve 32.5 mg Reference Standard (available,from American Cyanamid Co.) in methanol and dilute to 250 mL,with methanol. (2) Working solution.—13 mg/mL. Dilute 25 mL,aliquot stock solution to 250 mL with methanol.,B. Preparation of Laboratory Sample,Grind test laboratory sample in high-speed blender with methanol–,CHCl3 (2 + 1) in ratio of 400 mL solvent/100 g laboratoy sample.,Filter with suction through 2 Whatman No. 1, or equivalent,papers in Büchner, and wash pulp with methanol–CHCl3 (2 + 1), using,100 mL/100 g laboratory sample. Determine volume of solution,and transfer portion equivalent to 50 g laboratory sample to 400 mL,beaker.,C. Determination,Add several glass beads and 1mL HCl to beaker, and evaporate to,50 mL on steam bath. Add 30 mL 30% NaCl solution and 100 mL,methanol. Cool, transfer to 500 mL separator, and extract gently,with 50 mL CCl4 by inverting separator 6–8 times. Let phases separate,and discard CCl4 layer. Repeat with 50mLCCl4, inverting separator,ca twice as many times. Discard CCl4; then extract with 50 mL,CCl4, shaking gently 30 s. Finally, extract with 50 mL CCl4, shaking,vigorously 1 min, and again discard CCl4.,Adjust pH of solution to ca 5.5 with 4M NaOH (pH meter), and,add 20 mL pH 5.5 buffer and 20 mL bromocresol purple solution,A(a). Re-adjust pH to 5.5 and extract complex with two 50 mL portions,CHCl3, shaking 2 min each time. Shake combined extract 30 s,with 25 mL pH 5.5 buffer, A(b), and transfer CHCl3 layer to another,separator. Shake 1 min with 25 mL pH 5.5 buffer, A(b), let stand,10 min, and transfer CHCl3 to another separator. Shake with 20 mL,0.05M NaOH to remove all combined indicator and any organic acids,which may persist. Recomplex dodecylguanidine (in CHCl3 as free,base) by shaking 3 min with 5 mL bromocresol purple solution ,A(a),and 20 mL pH 5.5 buffer, A(b). Wash CHCl3 with three 15 mL,portions pH 5.5 buffer, A(b),shaking 1 min each time. Transfer CHCl3,to dry 250 mL separator and shake 2 min with 20 mL 0.05M NaOH,measured by pipet. Read A of indicator in aqueous solution at 590 nm,using Beckman spectrophotometer, or equivalent. Obtain mg DDGA,from standard curve.,D. Preparation of Standard Curve,Add 0.5, 1.0, 2.0, 3.0, 4.0, and 5.0 mL standard solution, A(c), to,series of separators containing 100 mL methanol, 50 mL H2O, 30 mL,30% NaCl solution, 20 mL bromocresol purple solution,, A(a), and,20 mL pH 5.5 buffer, A(b). Adjust pH of each solution to 5.5 and continue,as in C, paragraph 2, beginning “. . . and extract complex with,two 50 mL portions CHCl3, shaking 2 min each time.” Read A of,each aqueous solution at 590 nm and plot against mg DDGA. No,blank correction is necessary for standards.,mg/g (ppm) DDGA =,mg DDGA in aliquot/g test portion in aliquot,Reference: JAOAC 47, 300(1964).,CAS-2439-10-3 (dodine),. 2000 AOAC INTERNATIONAL……
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