AOAC Official Method 999 aoac9.1.09
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AD639CDE82CA47B39EB4C5C3E7349FE1 |
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0.03 |
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3 |
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日期： |
2024-7-30 |
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9.1.09,AOAC Official Method 999.11,Determination of Lead, Cadmium,Copper, Iron, and Zinc,in Foods,Atomic Absorption Spectrophotometry,after Dry Ashing,First Action 1999,NMLK–AOAC Method,[Applicable to the determination of lead, cadmium, zinc, copper,and iron in food by dry ashing and flame atomic absorption spectrometry,(GFAAS), flame and graphite furnace procedures. See Table,999.11A for the results of the interlaboratory study supporting,the acceptance of the method.],Caution: Always gently add acid to water.,Avoid environmental contamination by Pb. Store quartz crucibles,in20%HNO3 and rinse with deionized water before use. When necessary,crucibles may be boiled with 20%HNO3 before use. Heat platinumcrucibles,until red hot and boil with50%(v/v) HCl prior to use.,Ash products with a high fat content (340%), e.g., margarine or,lard, with great care to avoid self-ignition. Pre-ash such products according,to D(c)(2), even if a programmable furnace is used.,A. Principle,Test portions are dried and then ashed at 450°C under a gradual increase,(￡50°C/h) in temperature. 6M HCl (1 + 1) is added, and the,solution is evaporated to dryness. The residue is dissolved in 0.1M,HNO3, and the analytes are determined by flame and graphite procedures.,B. Apparatus,(a) Atomic absorption spectrophotometer.—With an air–acetylene,burner or nitrous oxide–acetylene burner for flame and a graphite,furnace for electrothermal determinations, with appropriate,background (nonatomic) correction (see Table 999.11B).,See Table 999.11C for example of instrumental parameters for,graphite furnace AAS. (The parameters listed are for a Perkin Elmer,HGA-500 instrument. For other instruments, the parameters may,have to be changed. Suitable parameters are usually given in the,manual provided with the instrument.),. 2002 AOAC INTERNATIONAL,Table 999.11A Interlaboratory study results,Metal Sample Analyte range Mean, mg/kg na sr,b sR,c RSDr,d RSDR,e rf Rg,Pb-HGAAS Liver paste/milk powder 30.04 0.040 11 0.019 0.019 46 46 0.052 0.052,Apple sauce 0.27 10 0.10 38 0.29,Minced fish 0.53 10 0.11 20 0.31,Wheat bran 0.111 12 0.056 50 0.16,Simulated diets D/E 0.246 10[1] 0.034 0.048 14 20 0.096 0.14,Cd-HGAAS Liver paste 30.05 0.0491 11 0.0058 12 0.016,Minced fish/wheat bran 0.175 8[1] 0.021 0.032 12 18 0.058 0.089,Simulated diets D/E 0.51 8 0.10 0.13 19 26 0.27 0.37,Zn-FAAS Liver paste/minced fish 30.7 6.63 13 0.35 0.50 5.3 7.5 0.98 1.4,Apple sauce 0.699 11[3] 0.047 6.8 0.13,Wheat bran 71.5 12[2] 4.9 6.8 14,Milk powder 35.0 12[2] 2.8 8.0 7.9,Simulated diets D/E 37.82 11[2] 0.68 1.31 1.8 3.5 1.9 3.7,Cu-FAAS Apple sauce/minced fish 30.2 0.240 12[1] 0.076 0.076 32 32 0.21 0.21,Milk powder 0.51 14[2] 0.23 45 0.65,Liver paste 5.34 13[2] 0.37 6.9 1.0,Wheat bran 9.52 12 0.98 10 2.7,Simulated diets D/E 45.4 12[1] 1.6 3.1 3.6 6.9 4.6 8.8,Fe-FAAS Liver paste 34 24.3 14 2.8 11 7.8,Minced fish/milk powder 3.99 11[3] 0.44 0.54 11 14 1.2 1.5,Wheat bran 124 13[1] 14 11 39,Simulated diets D/E 216 13 18 23 8.2 11 49 64,a n = Number of laboratories remaining after elimination of outliers [in brackets].,b sr = Repeatability standard deviation.,c sR = Reproducibility standard deviation.,d RSDr = Relative repeatability standard deviation.,e RSDR = Relative reproducibility standard deviation.,f r = 2.8 ′ sr.,g R = 2.8 ′ sR.,(b) Hollow cathode, or electrodeless discharge lamps for all elements,determined.,(c) Furnace.—Programmable, or muffle furnace with thermostat,maintaining 450 ± 25°C. If muffle furnace is used, a separate,pre-ashing device is required. See (d)–(h).,(d) Hot plate.—With heating control, to heat up to about 300°C.,(e) Lamp.—IR 250 W, fixed to a retort stand in a way that allows,adjustment of the distance to the plate.,(f) Ceramic plate.—e.g., Desiccator plate on a low stand, with a,diameter that suits the hot plate.,(g) Glass cover.—e.g., Crystallizing dish, 185 mm diameter,100 mm height, to fit on (f) or equivalent.,(h) Wash-bottle.—“Scrubber,” containing H2SO4 for purification,of air.,See Figure 999.11 for assembly of items (d)–(h).,(i) Quartz or platinum crucibles.—50–75 mL.,(j) Polystyrene bottles.—With leak-proof closures, 100 mL.,Carefully clean and rinse all glassware and plasticware with,HNO3 or HCl to avoid metal contamination. Cleaning procedure for,glass and plasticware.—Acid solution: 500 mL concentrated,HNO3,C(c) +4500 mL deionized water,C(a). Wash first with water,and detergent. Rinse with tap water, followed by deionized water,then with dilute acid. Finally rinse 4–5 times with deionized water.,C. Reagents,Reagents should be at least analytical reagent grade (p.a.), preferably,ultrapure (suprapur), or equivalent.,(a……
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