AOAC Official Method 935.13 Calcium in Animal Feed Wet Ash Method
First Action 1935
Final Action
A. Preparation of Solution
(a) Weigh 2.5 g test portion into 500 or 800 mL Kjeldahl flask.Add 20–30 mL HNO3 and boil gently 30–45 min to oxidize all easily oxidizable matter. Cool solution somewhat and add 10 mL 70–72% HClO4. Boil very gently, adjusting flame as necessary, until solution is colorless or nearly so and dense white fumes appear. Use particular care not to boil to dryness at any time. Cool slightly, add 50 mL H2O, and boil to drive out any remaining NO2 fumes. Cool, dilute, filter into 250 mL volumetric flask, dilute to volume, and mix thoroughly.
(b) Weigh 2.5 g finely ground test portion into SiO2 or porcelain dish and ignite as in 942.05 (see 4.1.10). Add 40 mL HCl (1 + 3) and few drops HNO3 to residue, boil, transfer to 250 mL volumetric flask, cool, dilute to volume, and mix thoroughly.
