AOAC Official Method 2001
|
ID： |
4876863DE5644B6CBE4C9ECD5762BB52 |
|
文件大小(MB)： |
0.03 |
|
页数： |
3 |
|
文件格式： |
|
|
日期： |
2024-7-30 |
|
购买： |
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）：
4.2.11,AOAC Official Method 2001.11,Protein (Crude) in Animal Feed,Forage (Plant Tissue), Grain, and Oilseeds,Block Digestion Method Using Copper Catalyst,and Steam Distillation into Boric Acid,First Action 2001,[Applicable to the determination of 0.5–50% Kjeldahl N,(3–300% equivalent crude protein) in forage, animal feed and pet,food, grain, and oilseeds, and applicable to the same matrixes as,976.05 (4.2.05), 976.06 (4.2.06), 984.13 (4.2.09), 988.05 (4.2.03),and 990.02 (4.2.07); the method does not measure oxidized forms of,N or heterocyclic N compounds.],See Tables 2001.11A and B for the results of the interlaboratory,study, expressed on a protein basis (N ′ 6.25), supporting acceptance,of the method.,A. Principle,The material is digested in H2SO4 to convert the protein N to,(NH4)2SO4 at a boiling point elevated by the addition of K2SO4 with,a Cu catalyst to enhance the reaction rate. Ammonia is liberated by,alkaline steam distillation and quantified titrimetrically with standardized,acid. Aluminum block heaters increase the efficiency of the,digestion.,The digest must contain residual H2SO4 to retain the NH3. Water,is added manually or automatically to the digest to avoid mixing,concentrated alkali with concentrated acid and to prevent the digest,from solidifying. Concentrated NaOH is added to neutralize the acid,and make the digest basic, and the liberatedNH3 is distilled into a boric,acid solution and titrated with a stronger standardized acid, HCl,to a colorimetric endpoint. The same endpoint detection system,(e.g., indicator, wavelength) must be used for the standardization of,the HCl and for the analyte.,The analyte is referred to as “crude” protein because the method,determines N, a component of all proteins. In addition, N from,sources other than true protein is also determined. (Additional digestion,procedures must be used in order to includeNfrom nitrate.) The,amount of protein in most materials is calculated by multiplying%N,by 6.25, because most proteins contain 16% N.,The H2SO4 and NaOH used are in concentrated form and are,highly corrosive. Wear gloves and eye protection while handling the,chemicals. Do not mix concentrated acid and NaOH directly. If,chemicals are splashed on the skin or in the eyes, flush with copious,amounts of water. Seek medical attention. Do not breathe the sulfur,oxide fumes produced during digestion.,B. Apparatus,(a) Digestion block.—Aluminum alloy block with adjustable,temperature device for measuring and controlling block temperature,(Tecator Digestion System 20, 1015 Digestor, Foss North America,7682 Executive Dr, Eden Prairie, MN 55344, USA;,+ 1 - 9 5 2 - 9 7 4 - 9 8 9 2 , F a x : + 1 - 9 5 2 - 9 7 4 - 9 8 2 3 ,info@fossnorthamerica.com; or equivalent).,(b) Digestion tubes.—250 mL.,(c) Distillation units.—(1) For steam distillation.—Foss,Tecator 2200, or equivalent, to accept 250 mL digestion tubes and,500 mL titration flasks. (2) For steam distillation and,autotitration.—Foss Tecator 2300, or equivalent.,(d) Titration flask.—500 mL graduated Erlenmeyer flask (for,collection and titration of distillate).,(e) Fume exhaust manifold.—With Teflon ring seals, connected,to a water aspirator in a hooded sink.,(f) Weighing paper.—Low N, Alfie Packers No. 201 (Alfie,Packers, Inc., 8901 J St, Ste 10, Omaha, NE 68127, USA), or Fisher,09-898-12A, 3 ′3 in. (76 ′ 76 mm), or equivalent.,(g) Pipetting dispenser.—25 mL, adjustable volume, attached to,a 5 pint (2.4 L) acid bottle.,C. Reagents,(a) Sulfuric acid.—Concentrated, 95–98% H2SO4, reagent,grade.,. 2002 AOAC INTERNATIONAL,Table 2001.11A Interlaboratory study results for the determination of crude protein by block digestion with a copper catalyst and,distillation into 4% boric acid,ID No. of labsa Mean, % RSDr, % RSDR, % HORRAT,Protein block 10(1) 40.19 0.45 0.76 0.333,Swine pellets 10(1) 37.04 0.47 0.60 0.256,Corn silage 11 7.10 1.64 2.16 0.726,Grass hay 11 7.11 1.94 1.94 0.650,Fish meal 11 64.67 0.73 0.98 0.460,Dog food 11 24.50 0.87 0.91 0.369,Chinchilla food 11 18.01 0.89 0.99 0.383,Albumin 10(1) 79.14 0.40 0.44 0.212,Birdseed 11 13.48 0.88 1.29 0.475,Meat and bone meal 11 50.06 1.90 1.90 0.857,Milk replacer 11 20.78 1.39 1.39 0.550,Soybeans 9(2) 38.76 0.49 0.54 0.236,Sunflower seeds 11 17.43 2.38 2.38 0.916,Legume hay 11 18.81 1.45 1.45 0.565,a Each value is the number of laboratories retained after elimination of outliers; each value in parentheses is the number of laboratories removed as outliers.,(b) Catalyst.—7.0 gK2SO4 + 0.8 g CuSO4. (Commercially available,in tablet form as 3.5 g K2SO4 and 0.4 g CuSO4 per tablet.),(c) Sodium hydroxide solution.—40% (w/w) NaOH, low N,(￡5 mg N/g).,(……
……