AOAC Official Method Moisture in Animal Feed

Transcription

1 Loss on Drying at C -Final Action AOAC Official Method Moisture in Animal Feed Dry amount of sample containing 2 g dry material to constant weight at C under pressure <100 mm Hg. For feeds with high molasses content, use temperature < 70 and pressure <50 mm. Use covered Al dish >50 mm diameter and 40mm deep. Report loss in weight as moisture. A. Apparatus AOAC Official Method Moisture in Animal Feed by distillation with Toluene Connect 250 ml flask of Pyrex or other resistant glass by means of Bidwell-Sterling moisture receiver to 500 mm Liebig condenser. Calibrate receiver, 5 ml capacity, by distilling known amounts water into graduated column, and estimating column of water to.01 ml. Clean tube and condenser with chromic acid cleaning mixture, rinse thoroughly with water, then alcohol, and dry in oven to prevent undue amount water from adhering to inner surfaces. B. Determination If sample is likely to bump, add dry sand to cover bottom of flask. Add enough toluene to cover sample completely. Weigh and introduce enough sample into toluene to give 2-5 ml water and connect apparatus. Fill receiving tube with toluene, pouring it through top of condenser. Bring to boil and distill slowly, 2 drops/sec, until most of water passes over, then increase rate of distillation to 4 drops/sec. When all water is over, wash down condenser by pouring toluene in at the top for a short time to see whether any more water distills over. If any water remains in condenser remove by brushing down with tube brush attached to copper wire and saturated with toluene, washing down condenser at the same time. Let receiving tube come to room temperature. If any drops adhere to sides of tube, force them down, using copper wire with end wrapped with rubber band. Then read volume of water and calculate to percent.

2 AOAC Official Method Moisture in Soft-Moist and Semi-Moist Pet Foods Karl Fischer Method First Action 1991First Action 1995 (Applicable to samples containing 20-30% moisture and other volatile materials.) Method Performance: S r = 0.3; S R = 0.4; RSD r = 1.1%; RSD R = 1.7% A. Principle Water is extracted with methanol from pet food that contains other volatile components, and aliquot is titrated with Karl Fischer reagent. B. Apparatus and Reagents (a) Karl Fischer titration assembly.- Manual or automatic, with stirrer. (b) Karl Fischer reagent.- Stabilized, single solution (Fisher Scientific Co., SK3, or equivalent). (Caution: If solution contains pyridine, see Appendix B, safety note on pyridine.) To standardize reagent, add 100 mg H 2 O from weighing pipet, or other suitable device, to ml pretitrated CH 3 OH, and titrate with Karl Fischer reagent. C = mg H 2 O/mL reagent. (c) Methanol.- ACS reagent grade. 99.8% CH 3 OH. 0.1% H 2 O % acetone. C. Sample Preparation Reduce sample to as fine condition as possible. Household-style blender may be used; shake blender back and forth to move sample into blades. D. Determination

3 Accurately weigh 8-10 g prepared sample into Erlenmeyer that contains magnetic stirring bar. Add 200 ml CH 3 OH, and stopper flask. Stir magnetically 15 min. Let solids settle. Transfer 10 ml aliquot to titration vessel containing pretitrated methanol and titrate with Karl Fischer reagent. Determine blank on 10 ml CH 3 OH as above and subtract from sample determination. Water, % = [2 * (ml reagent * C)]/g sample Reference: JAOAC 73, 399(1990). Revised: March 1996 AOAC Official Method Moisture and Volatile Matter In Oils and Fats Vacuum Oven Method Final Action Soften sample, if necessary, by gentle heat, taking care not to melt it. When soft enough, mix thoroughly with effective mechanical mixer. Weigh 5 +/- 0.2 g prepared sample into Al moisture dish ca 5 cm diameter and 2 cm deep with tight-fit slip-over cover. Dry to constant weight in vacuum oven at uniform temperature degrees above bp of H20 at working pressure, which should be </= 100 mm Hg (13.3 kpa). Cool in efficient desiccator 30 min and weigh. Constant weight is attained when successive 1 h drying periods show additional loss of </= 0.05%. Report % loss in weight as moisture and volatile matter. Reference: Ind. Eng. Chem. 18, 1347(1926). JAOAC 14, 247(1931); 15, 560(1932). AOAC Official Method

4 Moisture in Oils and Fats Karl Fischer Method First Action 1984 Final Action 1985 ISO/TC34/SC11/N99 - ACOC Method (Applicable to oils and fats except for alkaline or oxidized samples.) A. Apparatus and Reagents (A) Karl Fischer titration assembly Manual or automated, with stirrer. (B) Karl Fischer reagent Stabilized with H2) equivalent of ca 5 mg H20/mL reagent. Available commercially or prepare as follows: Dissolve 133g I2 in 425 ml dry pyridine in dry glass stoppered bottle. Add 425 ml dry ethylene glycol monomethyl ether. Cool to <4 degrees in ice bath and bubble in g So2. Mix well and let stand 12 h. Reagent is reasonably stable, but restandardize for each series of determinations. Standardize daily with sodium tartrate 2H2O. 1 mg sodium tartrate 2H2O = mg H2O. Alternatively, standardize with weighed H2O in methyl alcohol as follows: Transfer accurately weighed amount (50 mg) H2O to titration vessel and titrate to electrometric end point. Calculate C = mg H2O / ml reagent. (C) Karl Fischer reagent diluent 2 Methoxyethanol - pyridine (4+1). (D) Sample solvent Anhydrous CHCL3 - methyl alcohol (1+1) or (2+1). B. Determination Weigh to nearest 0.01 g, 5-25 g prepared sample, containing </= mg H2O, into tritation vessel, dissolve in anhydrous CHCl3 - methyl alcohol. Titrate with undiluted or diluted (1+1) Karl Fischer reagent to electrometric end point. Carry out blank test using same amount of reagent, diluent, and solvents. Subtract blank titer. % H2O = (ml reagent x C) / (g sample x 10) Note: Pyridine-free Karl Fischer reagents are available from laboratory reagent suppliers. Reference: JAOAC 67, 299(1984)

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