AOAC Final Action Methods in 2018

For infant formula, the test portion size is net 0.50 g of a powder sample, which should be taken from a reconstitution of 25 g powder in 200 g warm (50°C) water (e.g., 4.0 g of the reconstitution).] ( 4 )  Cheese .—Weigh 0.5–0.8 g to the nearest 1 mg into the MDC vessel. ( 5 )  Butter .—Weigh 0.5 g to the nearest 1 mg into the MDC vessel. ( 6 )  Blank .—In parallel with test portion digestions and analyses, carry out a blank test using the same procedures and reagents. ( 7 ) Carefully add 5.0 ± 0.1 mL HNO 3 into MDC vessel. Loosely cap MDC vessel without sealing. Predigest for at least 10 min at room temperature or until vigorous foaming subsides. Close MDC vessels and distribute onto microwave carousel to ensure uniform microwave power application on all samples. ( c )  Test portion preparation with MDO flask or tube .—( 1 )  Infant cereals or fortified milk powders .—Accurately weigh 1.00 ± 0.01 g into a 100 mL volumetric flask for MDO. ( 2 )  Milk and whey .—Weigh 4.0 g to the nearest 1 mg into the MDO flask or tube. ( 3 )  Dried milk, dried whey, and infant formula .—Weigh 1 g powdered product to the nearest 1 mg (or sample mass on a dry- weight basis in the prepared slurry) into the MDO flask or tube. ( 4 )  Cheese .—Weigh 0.3 g to the nearest 1 mg into the MDO flask or tube. ( 5 )  Butter .—Weigh 0.5 g to the nearest 1 mg into the MDO vessel. ( 6 )  Blank .—In parallel with test portion digestions and analyses, carry out a blank test using the same procedures and reagents. ( 7 ) Carefully add 5.0 ± 0.1 mL HNO 3 and then 5 mL H 2 O 2 into MDO flask or tube. Predigest for at least 10 min at room temperature or until vigorous foaming subsides. Distribute flasks or tubes onto microwave carousel to ensure uniform microwave power application on all samples. [ Note : An optimal analytical test portion mass of 0.5 g (1.0 g for MDO) is based on an empirical maximum energy release by the food of 3 kcal and 90–110% recovery.] [ Note : Line the MDC vessel walls or Pasteur pipet with weighing paper during sample transfer to keep sample from adhering to sides of vessel or use a Pasteur pipet to transfer liquid samples. Remove weighing paper from sample prior to next step. Weigh fluid samples or test portion from slurry test sample directly after mixing.) ( d )  Food-grade salt sample preparation .—Weigh 0.20 ± 0.01 g food-grade salt into a 100 mL volumetric flask. Add deionized water and 10 mL HNO 3 . Dissolve salt and dilute to volume with deionized water. ( e )  Test portion digestion .—( 1 )  MDC digestion .—With power setting appropriate to MDC (maximum power of 1600 W), and number of vessels used, ramp MDC temperature from ambient to 200 ± 20°C in 15 min and hold at 200°C for 25 min. Cool vessels to room temperature with cooling system on high for 15 min before venting. Transfer the MDC digests quantitatively to 50 mL volumetric flasks or 25 mL autosampler tubes. Dilute to volume with H 2 O and mix. [ Note : Final dilutions in volumetric flasks (e.g., 50 mL) or autosampler tubes (e.g., 25 mL) require the addition of appropriate amounts of HNO 3 for MDC digests to maintain the proportion of 10% (v/v) HNO 3 in the final solution to be analyzed.] ( Note : A digestion is judged complete when a clear to yellow analytical solution is produced.) ( 2 )  MDO digestion .—With power setting appropriate to MDO models (maximum power of 600 W), and number of vessels used, heat MDO vessels at 200 ± 20°C for 20 min. ( Note : Yellow vapors

( 2 )  Std5 .—Pipet 10 mL intermediate stock standard solution into a 100 mL acid-washed volumetric flask. Add 10 mL HNO 3 (MDC) or 15 mL combined acids (MDO), dilute to volume with H 2 O, mix, and transfer to acid-washed polyethylene bottle. ( 3 )  Std4 .—Pipet 5.0 mL intermediate stock standard solution into a 100 mL acid-washed volumetric flask. Add 10 mL HNO 3 (MDC) or 15 mL combined acids (MDO), dilute to volume with H 2 O, mix, and transfer to acid-washed polyethylene bottle. ( 4 )  Std3 .—Pipet 2.0 mL intermediate stock standard solution into a 100 mL acid-washed volumetric flask. Add 10 mL HNO 3 (MDC) or 15 mL combined acids (MDO), dilute to volume with H 2 O, mix, and transfer to acid-washed polyethylene bottle. ( 5 )  Std2 .—Pipet 1.0 mL intermediate stock standard solution into a 100 mL acid-washed volumetric flask. Add 10 mL HNO 3 (MDC) or 15 mL combined acids (MDO), dilute to volume with H 2 O, mix, and transfer to acid-washed polyethylene bottle. ( 6 )  Std1 .—Pipet 0.5 mL intermediate stock standard solution into a 100 mL acid-washed volumetric flask. Add 10 mL HNO 3 (MDC) or 15 mL combined acids (MDO), dilute to volume with H 2 O, mix, and transfer to acid-washed polyethylene bottle. ( 7 )  Blank .—Add 10 mL HNO 3 (MDC) or 15 mL combined acids (MDO) into a 100 mL acid-washed volumetric flask, dilute to volume with H 2 O, mix, and transfer to acid-washed polyethylene bottle. All calibration solutions when made are stable for 1 week in glass volumetric flasks. ( i )  Sampler wash solution, 10% HNO 3 (v/v) .—Dilute 100 mL trace metal-grade HNO 3 to 1000 mL with H 2 O. D. Sample Preparation and Digestion ( a )  Sample preparation .—( 1 ) Homogenize a representative sample by grinding as finely as possible and/or by preparing a slurry with H 2 O. ( 2 ) For infant cereals and fortified milk powders, preheat water at 50°C. Prepare the slurry by weighing 10.0 ± 0.1 g test sample and place into a 100 mL Erlenmeyer flask; add 90.0 ± 0.1 g H 2 O. Mix well with stopper. ( 3 ) For milk and whey, place the test sample in a water bath at 20°C and mix carefully. If the fat is not evenly dispersed, warm the test sample slowly in a water bath at 40°C, mix gently by inversion only, and cool quickly in the water bath at 20°C. ( 4 ) For dried milk, dried whey, and infant formula, transfer the test sample to a container with an airtight lid of twice the sample volume, close the container immediately, and mix by repeatedly shaking and inverting the container. ( 5 ) For cheese, remove the rind or surface layer so as to provide a test sample representative of the cheese as it is normally consumed. Grind the test sample with an appropriate device, mix the whole mass, and grind again quickly. If the test sample cannot be ground (e.g., soft cheese), mix the test sample thoroughly. ( 6 ) Transfer the homogenized sample to an airtight container immediately. Analyze test sample as soon as possible after homogenization. Do not analyze ground cheese that shows unwanted mold growth or deterioration. ( b )  Test portion preparation with MDC vessel .—( 1 )  Infant cereals or fortified milk powders .—Accurately weigh 0.50 ± 0.01 g test portion or sample mass on a dry weight basis in the prepared slurry to MDC vessel. ( 2 )  Milk and whey .—Weigh 4.0 g to the nearest 1 mg into the MDC vessel. ( 3 )  Dried milk, dried whey, and infant formula .—Weigh 0.5 g powdered product to the nearest 1 mg into the MDC vessel. [ Note :

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