AOAC Official Method 922
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E053ED0A9778496F8224CBF28D3E1233 |
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0.01 |
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1 |
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日期： |
2024-7-30 |
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7.1.10,AOAC Official Method 922.05,Copper in Pesticide Formulations,First Action 1922,Final Action,(Applicable to such preparations as Bordeaux–lead arsenate, Bordeaux–,zinc arsenite, Bordeaux–Paris green, and Bordeaux–calcium,arsenate.),A. Electrolytic Method,Evaporate filtrate and washings from PbSO4 precipitation, 922.04,(see 7.1.09), to fuming; add few mL fuming HNO3 to destroy organic,matter, and continue evaporation to ca 3 mL. Take up with ca,150 mL H2O, add 5 mL HNO3, and filter if necessary. Wash into,250 mL beaker, adjust volume to 200 mL, and electrolyze, using rotating,anode and weighed gauze cathode with current of 2–3 amp.,After all Cu has apparently deposited (ca 30 min), add 15–20 mL,H2O to electrolyte and continue electrolysis few min. If no further,deposition occurs on newly exposed surface of electrode, wash with,H2O without breaking current either by siphoning or quickly replacing,beaker with electrolyte successively with 2 beakers of H2O. Interrupt,current, rinse cathode with alcohol, dry few moments in,oven, and weigh. Calculate percent Cu in test portion.,B. Volumetric Thiosulfate Method,Proceed as in A to point at which filtrate and washings from,PbSO4 precipitation are treated with fuming HNO3 and evaporated,to volume of ca 3 mL. Take up in ca 50 mL H2O, add NH4OH in excess,and boil to expel excess NH3, as shown by color change in liquid,and partial precipitation. Add 3–4 mL CH3COOH (4 + 1), boil,1–2 min, cool, add 10 mL 30% KI solution (w/v), and titrate with,standard Na2S2O3 solution until brown color becomes faint. Add,starch indicator, 922.03A(f) (see 7.1.05), and continue titration cautiously,until blue color due to free I2 entirely disappears. From mL,standard Na2S2O3 solution used, calculate percent Cu in test portion.,Thiosulfate standard solution.—Prepare solution containing 39 g,Na2S2O3×5H2O/L. Accurately weigh 0.2–0.4 g pure electrolytic Cu,and transfer to 250 mL Erlenmeyer roughly marked at 20 mL intervals.,Dissolve Cu in 5mLHNO3 (1 + 1), dilute to 20 or 30 mL, boil to,expel red fumes, add slight excess saturated Br2–H2O, and boil until,Br2 is completely removed. Cool, and add 10 mL NaCH3COO solution,(574 g trihydrate/L). Prepare 42 g/100 mL KI solution made,very slightly alkaline to avoid formation and oxidation of HI. Add,10 mL of the KI solution and titrate with Na2S2O3 solution to light,yellow. Add enough starch indicator, 922.03A(f) (see 7.1.05), to,produce marked blue. As end point nears, add 2 g KSCN and stir until,completely dissolved. Continue titration until precipitate is perfectly,white. 1 mL Na2S2O3 solution = ca 10 mg Cu.,It is essential for Na2S2O3 titration that concentration of KI in solution,be carefully regulated. If solution contains <320 mg Cu, at,completion of titration 4.2–5 g KI should have been added for each,100 mL total solution. If greater amounts of Cu are present, add KI,solution slowly from buret with constant agitation in amounts proportionately,greater.,Reference: JAOAC 5, 398(1922).,CAS-7440-50-8 (copper),. 2000 AOAC INTERNATIONAL……
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