AOAC Official Method 958
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85E9EA30EDA74F248B0CE2C7EAA8D03F |
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0.03 |
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2 |
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日期： |
2024-7-30 |
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10.6.03,AOAC Official Surplus Method 958.07i,Lindane and Technical BHC,Pesticide Residues,Distinguishing Method,First Action,Surplus 1970,10th ed.,24.106 Principles,BHC is extd with n-hexane. Ext. is refluxed over,fuming H SO and BHC is extd with acetonitrile. 2 4,Purified ext. is chromatographed on paper to sep. and,identify pesticides.,24.107 Reagents,(a) n-Hexane.—Tech. grade, 95 mole % min.,redistd.,(b) Acetonitrile.—Commercial grade, redistd.,(c) Fuming sulfuric acid.—30% free SO . 3,(d) Immobile solvent.—N,N-Dimethylformamide,b.p. 152–154E, 2-phenoxyethanol, m.p. 12–14E, and,ethyl ether, 10:2:88 (v/v).,(e) Mobile solvent.—2,2,4-Trimethylpentane, 99,mole % min.,(f) Chromogenic agent.—Dissolve 1.7 g AgNO in 3,H O, add 10 mL 2-phenoxyethanol and 50 mL EtOH, 2,and dil. with H O to 200 mL. (If temp. changes cause 2,sepn of 2-phenoxyethanol, add EtOH in 1 mL,increments, with mixing, until redissolved.),(g) Benzene hexachloride std soln.—Tech. grade,(10–15% (-isomer), 50 mg/10 mL EtOAc.,(h) Lindane std soln.—99+% (-isomer, 50 mg/10 mL,EtOAc.,(i) Benzene hexachloride-lindane std soln.—40 mg,BHC + 10 mg lindane/10 mL EtOAc.,(j) Chromatographic paper.—Whatman No. 1, 8 × 8",sheets. (If paper contains excessive amount of Agreacting,material, wash thoroly with distd H O and dry 2,in air or in oven at 100E.),24.108 Apparatus,(a) Chromatographic chamber.—For ascending,chromatography with 8 × 8" sheets. Construct tanks, 9",long × 9" high × 3?" wide, from light stainless steel.,From ?" strips of the metal, form 2 supports and,suspend flush with top from notches on sides as corners,of tank. (Arthur H. Thomas Co. No. 3106-F10 has been,found suitable.),(b) Atomizer.—Sprayer with reservoir calibrated at,10 mL intervals for use with adjustable constant,pressure air supply.,(c) Strong ultraviolet light source.—Such as,germicidal lamps (General Electric Co., Cleveland,Ohio), either (1) two 30 watt, 36" tubes, mounted in,reflectors ca 8" above papers; or (2) two 15 watt, 18",tubes, mounted in desk lamp fixture ca 4" above papers.,24.109 Determination,(a) Extraction.—Select wt material representative of,sample (ca 1000 g, or entire contents of small unit pkg),and comminute in food chopper. Transfer 100 g wellmixed,sample to high speed blender with 100 mL H O. 2,Add 100 g anhyd. Na SO and 200 mL n-hexane, line 2 4,blender cover with Al foil, and blend to uniform slurry,then 5 min. more. Transfer to two 250 mL centrifuge,bottles with stoppers covered with Al foil, and,centrifuge 5 min. Siphon off as much hexane phase as,possible (siphon described in 947.07 (See 33.6.13) is,convenient). Puncture caked plant material with thick,glass rod at opposite points on bottle wall, and pour off,and discard aq. phase. Break up cake with rod,centrifuge, and decant and combine hexane fractions.,Add 10 g anhyd. Na SO , shake, and filter thru rapid 2 4,paper into graduated cylinder. If total of <100 mL,hexane is recovered, discard first ext., take another 100,g portion comminuted product, and repeat from,"Transfer 100 g well-mixed sample," increasing amount,of solvent so that at least 50% of the hexane is finally,recovered.,(b) Purification of extract.—Transfer total ext.,noting vol., to 200 mL standard taper 24/40 erlenmeyer,(preferably lipped). Adjust vol. to ca 50 mL by evapg,solvent on steam bath with aid of jet of air. Add 10 mL,fuming H SO (caution!), insert standard taper air 2 4,condenser, and reflux on steam bath 30 min. Cool, pour,mixt. into dry 125 mL separator (lubricate all separator,only with n-hexane), and drain and discard free-flowing,portion of the acid. Decant hexane into another dry,reflux app., rinse flask and separator with 5 mL hexane,and add rinsing to reflux app. Add 10 mL fuming,H SO , reflux, sep. acid, and rinse as before, collecting 2 4,hexane in 125 mL g-s. flas. Add three 100 mg portions,filter aid (diatomaccous earth, such as Hyflo Super-,Cel), swirling ca 30 sec. after each addn. Filter thru 9,cm acid-resistant paper (Whitman No. 50 or equiv.) into,250 mL separator. Rinse flask twice with 5 mL hexane,and add washings to filter, letting filter drain between,addns.,Ext. hexane with four 60 mL portions H O, shaking 2,gently to avoid emulsions. Discard aq. phase, leaving,any emulsion. Add H O to completely fill separator, 2,and drain and discard aq. phase. (If emulsion is present spot aliquots to obtain spots to approx. intensities of,after final washing, add anhyd. Na SO in excess of spots obtained from stds. 2 4,satn, draw off any aq. phase that may have formed, and,filter hexane thru rapid paper into 250 mL separator,washing first separator ans filter with two 5 mL,portions hexane……
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