AOAC Official Method 970
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9AE38B927BD64E52BA626E33622F19ED |
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0.03 |
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2 |
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日期： |
2024-7-30 |
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文本摘录（文本识别可能有误，但文件阅览显示及打印正常，pdf文件可进行文字搜索定位）：
10.3.03,AOAC Official Method 970.53?,Organophosphorus,Pesticide Residues,Single Sweep Oscillographic,Polarographic Confirmatory Method,First Action 1970,Final Action 1974,Surplus 1994,(Applicable to diazinon, malathion, methyl parathion, and parathion.),A. Apparatus,(Wash all glassware with hot HNO3 [1 + 1] and rinse with H2O.),(a) Polarograph.—Any voltammetric or polarographic instrument,capable of linear sweep voltammetry at 10 ng pesticide/mL cell,solution (equivalent to 0.01 ppm (mg/mL) based on 1 g test portion in,1 mL cell solution).,(b) Silver wire electrode.—Deposit very thin coating of AgCl on,No. 20 or 22 gage Ag wire as follows: Dip wire in 10% HNO3, rinse,in H2O, and then let stand 10 min in 1M HCl.,B. Reagents,(a) Acetonitrile.—Distilled in glass at 82 ± 1°C.,(b) Acetone.—Distil at 56.5°C with 0.25 g KMnO4/L. Distillation,must be performed as directed.,(c) Ethyl acetate.—Distilled in glass at 77 ± 1°C.,(d) Petroleum ether.—Distilled in glass at 30–60°C.,(e) Nitrogen.—Prepurified, H2O-pumped.,(f) Tetramethyl ammonium bromide.—Eastman Kodak No. 670,or equivalent.,(g) Electrolyte solutions.—(1) For diazinon.—Dissolve 7.7 g,(CH3)4NBr in 300 mL H2O. Add 115 mL CH3COOH and dilute to,500 mL with H2O. (2) For malathion.—Dissolve 15.4 g (CH3)4NBr,in 300 mL H2O. Add 0.2 g LiCl and 4.1 mL HCl, and dilute to,500 mL with H2O. (3) For methyl parathion and parathion.—Dissolve,2.2 g NaCH3COO×3H2O and 1.17 g NaCl in 100 mL H2O and,adjust to pH 4.8 with CH3COOH, using pH meter.,(h) Pesticide standard solutions.—(1) Stock solutions.—Prepare,individual solutions containing 1.00 mg pesticide/mL ethyl acetate.,Store at 0°C. (2) Intermediate solutions.—0.2 mg/mL. Transfer,5 stock solution to 25 mL volumetric flask and dilute to volume with,petroleum ether for diazinon, methanol for malathion, and acetone,for methyl parathion and parathion.,C. Preparation of Standard Curves,(a) Diazinon.—Transfer 0.0, 1.0, 2.0, 3.0, 4.0, and 5.0 mL intermediate,standard solution of diazinon to individual 100 mL volumetric,flasks and dilute to volume with petroleum ether. Transfer,1.0 mL of each solution to separate 50 mL Erlenmeyers and evaporate,to incipient dryness under gentle jet of dry air. Evaporate remaining,solvent with warmth of hand. Dissolve residue in 5.0 mL,electrolyte solution, (g)(1). Transfer solution to polarographic cell,adjust to 25 ± 1°C, and bubble N2 through solution 5 min. Polarograph,between -0.70 and -1.2 V against either Hg pool or Ag wire,reference electrode.,Peak potential for diazinon at 25°C is -0.90 ± 0.05 V against either,electrode. Plot mg diazinon/mL cell solution against peak height,in units instrument sensitivity setting.,(b) Malathion.—Transfer 0.0, 1.0, 2.0, 3.0, 4.0, and 5.0mLintermediate,standard solution of malathion to individual 25 mL volumetric,flasks and dilute to volume with methanol. Transfer 2.0mLof,each solution to separate 50 mL Erlenmeyers and add 1.0 mL 0.1M,KOH. After 3 min, add 2.0 mL electrolyte solution, (g)(2), mix well,and let stand 5 min. Transfer to polarographic cell, adjust to 25 ±,1°C, and bubble N2 through solution 5 min. Polarograph between,-0.5 and -1.0 V against either Hg pool or Ag wire electrode.,Peak potential for malathion at 25°C is –0.82 ± 0.05 V against Ag,wire and -0.85 ± 0.05 V against Hg pool reference electrodes. Plot,mg malathion/mL cell solution against peak height in units instrument,sensitivity setting. (Note: Compound actually polarographed,is fumaric acid resulting from basic hydrolysis of malathion.),(c) Parathion and methyl parathion.—Transfer 0.0, 1.0, 2.0,3.0, 4.0, and 5.0 mL intermediate parathion (or methyl parathion),standard solution to individual 100mLvolumetric flasks and dilute,to volume with acetone. Transfer 5.0 mL aliquots of each solution,to separate 50 mL Erlenmeyers, add 5.0 mL electrolyte solution,(g)(3), mix well, and transfer ca 5mL to polarographic cell. Adjust,to 25 ± 1°C, bubbleN2 through solution 5 min, and polarograph between,–0.4 and –0.9 V against either Hg pool or Ag wire reference,electrode.,Peak potential for parathion and methyl parathion at 25°C is,–0.68 ± 0.05 V against Hg pool and –0.70 ± 0.05 V against Ag wire,reference electrodes. Plot mg pesticide/mL cell solution (10 mL),against peak height in units ′ instrument sensitivity setting. Cell solution,volume = 5 mL extract + 5 mL electrolyte solution.,D. Preparation of Extracts,Prepare, extract, and clean up test portions as in 970.52K–O (see,10.1.01). Concentrate 15% and 50% eluates from Florisil column to,suitable definite volume in K–D concentrator. All eluting solvents,must be peroxide-free by test in Definitions and Explanatory Ter……
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