AOAC Official Method 974
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15DCBFA39C1C40888B0263704CDF1E58 |
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0.03 |
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2 |
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日期： |
2024-7-30 |
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10.3.01,AOAC Offical Method 974.22?,Organophosphorus Pesticide Residues,Carbon Column Cleanup Method,First Action 1974,Final Action 1976,Surplus 1994,(CH3CN extraction and charcoal cleanup column using KCl thermionic,or flame photometric detector for residues of parathion,paraoxon, carbophenothion and itsOanalog, and EPN on apples and,green beans.),A. Reagents,(a) Solvents.—Redistilled from glass (see 970.52A [see,10.1.01]): ethyl acetate, CH2Cl2, benzene, hexane, CH3CN, and,isopropanol.,(b) Acid-treated charcoal.—Slurry 200 g acid-treated charcoal,with 500 mL HCl, cover with watch glass, and stir magnetically,while boiling 1 h. Add 500 mL H2O, stir, and boil additional,30 min. Collect charcoal in Büchner and wash with H2O until,washings are neutral to universal indicator paper. Dry at 130°C in,forced-draft oven.,(c) Magnesium oxide.—See 970.52B(k) (see 10.1.01).,(d) Adsorbent mixture.—Mix one part acid-treated charcoal,2 parts hydrated MgO, and 4 parts Celite 545, acid washed. Keep,sealed.,(e) Pesticide standard solutions.—Prepare solutions containing,1 mg/mL ethyl acetate of each of following: parathion, paraoxon,carbophenothion, carbophenothion O analog, and EPN.,(f) Eluting solution.—CH3CN–benzene (1 + 1). Purity,test.—Reagents must be free of substances causing KCl thermionic,or flame photometric detector response, as indicated by following,test: Carry reagents through entire method, and inject 5 mL from final,concentrate into gas chromatograph, using conditions described,in 968.24F (see 10.3.02). Concentrate must not cause recorder deflection,>1 mm from baseline for 2–60 min after injection.,B. Apparatus,See also 970.52E (see 10.1.01) and 968.24B(a) (see 10.3.02).,(a) Vacuum adapter.—Kontes Glass Co., No. 954002, or equivalent.,(b) Gas chromatograph.—With potassium chloride thermionic,detector [see 968.24B(i) and (k) (see 10.3.02)] or flame photometric,detector [see 974.22B(e) and (i)].,(c) Column.—See 968.24B(j) (see 10.3.02).,(d) Potassium chloride thermionic detector (KClTD).—See,970.52H(d)(1) or (2), (e), (f), and (k) (see 10.1.01). Also check linearity,of GC system to paraoxon and carbophenothion O analog.,(e) Flame photometric detector (FPD).—With P selective optical,filter for 526 nm wavelength (Tracor Instruments, Inc.). Equivalent,to KClTD for determination of organophosphorus pesticides in,fruits and vegetables. (Note: Older commercial models of FPD may,give rise to adsorption and/or degradation of O analogs of,organophosphorus pesticides within detector’s gas mixing chamber.,Design changes of detectors manufactured after mid-1973 have generally,corrected this problem. Flameout in FPD, on injection of test,portion extract, can be avoided by letting H2 enter detector [lower,part] so that H2 and GC column effluent mix before burner area.,Air–O2 enters detector through upper part. This arrangement reverses,that recommended by manufacturer. Specifications for physical,modification of FPD to correct above problems are available from,Division of Chemistry and Physics, U.S. Food and Drug Administration,Washington,DC20204 USA.) Use highly stabilized 0–750Vdc,variable power supply capable of 10maoutput (Keithley Instruments,Inc., 28775 Aurora Rd, Cleveland, OH 44139 USA, or equivalent),6.3Vac ignitor power supply, electrometer with bucking capability of,1 ′ 10-6 A (Tracor Instruments, Inc., or equivalent), and variable,transformer capable of delivering 150 watts to control temperature,of flame housing. Strip chart recorder should be compatible with,electrometer.,(f) Hydrogen.—From cylinder of compressed H2 gas. Equip cylinder,with regulator, delivery line, and variable flow controller capable,of 200 mL/min delivery. Metering shut-off valve is required,separate from controller.,(g) Air.—Cylinder of compressed air equipped as in (f) to deliver,up to 100 mL/min. Separate shut-off valve is not needed.,(h) Oxygen.—Cylinder of compressed O2 gas equipped as in (f),to deliver up to 50 mL/min. Combine with air using standard,Swagelok tee before detector inlet.,(i) Flame photometric detector operation.—Adjust temperature,of burner housing to ca 170–180°C before igniting flame. Temperature,will rise 20–30°C after ignition. Do not allow detector to exceed,220°C. Adjust gas flows at controllers to ca 150–300 mL/min H2,50–100 mL/min air, and 5–20 mL/min O2. Adjust column effluent,flow, 970.52R(a) (see 10.1.01), to 120mLN2/min. Turn offH2 flow,with metering shut-off valve (f). (Caution: Before attempting ignition,make certainH2 has been purged from detector with other gases.,One min interval between ignition attempts is adequate.) Apply ca,750 V to photomultiplier tube from power s……
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