AOAC Official Method 990
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B7250E00379145B3B654239BB3362191 |
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0.05 |
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5 |
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日期： |
2024-7-30 |
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10.2.03,AOAC Official Method 990.06,Organochlorine Pesticides in Water,Gas Chromatographic Method,First Action 1990,Final Action 1993,(Applicable to determination of 29 organochlorine pesticides in,drinking water.),See Table 990.06A for the results of the interlaboratory study.,A. Principle,Measured volume of test portion (1 L) is extracted with CH2Cl2,by shaking in separatory funnel or mechanical tumbling in bottle.,CH2Cl2 extract is separated, dried with anhydrous Na2SO4, solvent,exchanged with methyl tert-butyl ether (MTBE), and concentrated,to 5 mL. Pesticides are separated and measured by capillary column,gas chromatography with electron-capture detection. Estimated,method detection limits range from 0.0015 mg/L for a- and g-chlordane,to 5 mg/L for chlorobenzilate; values for 24 compounds range,between 0.025 and 0.5 mg/L.,B. Apparatus,(a) Separatory funnel.—2000 mL, with TFE-fluorocarbon stopcock,and ground-glass or TFE-fluorocarbon stopper.,(b) Tumbler bottle.—1.7 L (Wheaton Roller Culture Vessel),with TFE-fluorocarbon lined screw cap. Cut liners to fit screw cap,from sheets (Pierce Catalog No. 012736) and extract overnight with,methanol before use.,(c) Kuderna–Danish (K–D) apparatus.—(1) Concentrator,tube.—10 or 25 mL, graduated (Kontes 570050-1025 or,570050-2525, or equivalent). Check calibration of concentrator tube,at volumes used in method. Use ground-glass stoppers to prevent,evaporation of extracts. (2) Evaporation flask.—500 mL (Kontes,570001-0500, or equivalent). Attach to concentrator tube with springs.,(3) Snyder columns.—Three-ball macro (Kontes 503000-0121, or,equivalent); 2-ball micro (Kontes 569001-0219, or equivalent).,(d) Vials.—Glass, 5–10 mL capacity, with TFE-fluorocarbon,lined screw caps.,(e) Separatory funnel shaker.—Capable of holding 2 L separatory,funnels and shaking them with rocking motion to thoroughly,mix funnel contents (Eberbach Co., Ann Arbor, MI USA).,(f) Tumbler.—Capable of holding and tumbling bottles, (b),end-over-end at 30 turns/min (Associated Design and Manufacturing,Co., Alexandria, VA USA).,(g) Boiling stones.—Carborundum, No. 12 granules (Thomas,Scientific, No. 1590-033). Heat 30 min at 400°C before use. Cool,and store in desiccator.,(h) Water bath.—Heated, capable of control ±2°C. Use bath in,hood.,(i) Balance.—Analytical, capable of accurately weighing to,nearest 0.0001 g.,(j) Gas chromatograph.—Temperature-programmable system,suitable for use with capillary columns, including syringes, analytical,columns, gases, detector, and strip chart recorder. Data system is,recommended for measuring peak areas. Primary column: 30 m ′,0.25mmid DB-5 fused-silica capillary column, 0.25 mmfilm thickness,(J&W Scientific, Inc.). Confirmation column: 30 m ′0.25 mm,id DB-1701 fused silica capillary column, 0.25 mm film thickness,(J&W Scientific, Inc.). Operating conditions: injection volume 2 mL,splitless with 45 s delay; He carrier gas at 30 cm/s linear velocity; injector,250°C; detector 320°C; oven programmed from 60–300°C at,4°C/min; electron capture detector.,C. Reagents,(a) Standard solutions.—Use standards of test compounds with,purity 396% to prepare stock solutions at 1 mg/mL in methyl,tert-butyl ether (MTBE). Commercially prepared stock standards,may be used at any concentration if they are certified by manufacturer,or independent source. Store solutions at room temperature,and protect from light. Replace stock standard solutions after 2,months, or sooner if comparison with laboratory control standards,indicates degradation.,( b ) I n t e r n a l s t a n d a r d s o l u t i o n . — P r e p a r e,pentachloronitrobenzene (purity 398%) stock solution at 0.1 mg/mL,in MTBE. Add 5 mL stock solution to 5 mL test portion extract to,give final internal standard concentration of 0.1 mg,pentachloronitrobenzene/mL of extract.,(c) Surrogate solution.—Prepare 4,4￠-dichlorobiphenyl (purity,396%) stock solution at 0.5 mg/mL in MTBE. Add 50 mL stock solution,to 1 L test sample prior to extraction to produce surrogate concentration,of 25 mg 4,4￠-dichlorobiphenyl/L in test sample and,assuming quantitative recovery, 5.0 mg/mL in extract.,(d) Instrument performance solution.—Prepare individual stock,standard solutions containing chlorothalonil, chlorpyrifos, DCPA,and d-BHC at 0.10 mg/mL in MTBE. For assessing instrument performance,combine 50 mL chlorothalonil stock solution, 2 mL,chlorpyrifos stock solution, 50 mL DCPA stock solution, and 40 mL,d-BHC stock solution in 100 mL volumetric flask and dilute to volume,with MTBE.,(e) Solvents.—Acetone, methylene chloride, and MTBE. Distilled-,in-glass quality, or equivalent.,(f) Phosphate buffer.—pH 7. Mix 29.6……
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