AOAC Methods for Review in Codex STAN 234_11-2018

AOAC Official Methods Listed in CXS 234 for Milk and Milk Products

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A.1.13

AOAC Official Method 942.27 Standard Solutions of Sodium Thiosulfate First Action 1942 Final Action

A. Preparation of Standard Solution Dissolve ca 25 g Na 2 S 2 O 3 @ 5H 2 O. Boil gently 5 min and transfer while hot to storage bottle previously cleaned with hot chromic acid cleaning solution and rinsed with warm boiled water. (Temper bottle, if not heat-resistant, before adding hot solution.) Store solution in dark, cool place; do not return unused portions to stock bottle. If solutions less concentrated than 0.1M are desired, prepare by dilution with boiled water. (More dilute solutions are less stable and should be prepared just before use.) B. Standardization Accurately weigh 0.20–0.23 g K 2 Cr 2 O 7 (NIST SRM 136e dried 2 h at 100 ° C) and place in glass-stoppered iodine flask (or glass-stoppered flask). Dissolve in 80 mL chlorine-free water containing 2 g KI. Add, with swirling, 20 mL ca 1M HCl and immediately place in dark 10 min. Titrate with Na 2 S 2 O 3 solution, A , adding starch solution after most of I 2 has been consumed. Molarity (mol/L) = g K 2 Cr 2 O 7 × 1000/mL Na 2 S 2 O 3 × 49.032 References: JAOAC 25 , 659(1942); 27 , 557(1944); 28 , 594(1945); 38 , 382(1955); 47 , 43, 46(1964); 48 , 103(1965). O in 1 LH 2

 2005 AOAC INTERNATIONAL

10/9/2018

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