AOAC Methods for Review in Codex STAN 234_11-2018

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

9

A.1.02

( b ) Reference solution .—To mixture of 5 mLHNO 3 ferric alum solution, 941.18D ( a ) ( see A.1.11), and 115 mLH 2 ca 0.02 mL 0.1M thiocyanate, B , noting exact volume used. B. Preparation of Standard Solution Prepare ca 0.1M solution from reagent that shows no chlorine using 7.612 g NH 4 SCN or 9.718 g KSCN/L. C. Standardization Accurately weigh, on tared watch glass, enough purified AgNO 3 to give titration of ca 40mL(ca 0.7 g for 0.1Msolution) and transfer with H 2 O through glass funnel to 250 mL glass-stoppered Erlenmeyer. Dissolve in ca 75mLH 2 O (halogen-free), and add 5mLHNO 3 (1 + 1) and 2 mL ferric alum solution, 941.18D ( a ) ( see A.1.11). Titrate with thiocyanate solution until titrated solution achieves a reddish brown color, which remains after shaking vigorously 1 min. Record buret reading and set flask aside 5 min, shaking occasionally and maintaining end point color by addition of thiocyanate solution as required. Then add additional thiocyanate solution, if necessary, to produce permanent end point color, matching with color of reference solution, A ( b ). From total volume thiocyanate solution used in titration, subtract volume contained in reference solution. (1 + 1), 2 mL O, add

AOAC Official Method 942.26 Standard Solutions of Ammonium and Potassium Thiocyanates First Action 1942 Final Action A. Reagents ( a ) Purified silver nitrate .—Dissolve 50 g AgNO 3 . Heat to dissolve, filter while still hot through fritted glass filter, using suction, and collect filtrate in clean borosilicate beaker. Wash beaker and filter with ca 5 mLhot water, adding washings to filtrate. Cool in ice bath, stirring to induce crystallization, and place in refrigerator at ca 10 ° C until equilibrium is reached. Decant liquid through fritted glass filter and transfer crystals to filter. Cover filter with watch glass and draw air through filter to remove adhering liquid. Transfer crystals to small, clean borosilicate beaker. Cover beaker with watch glass and place inside larger covered borosilicate beaker. Dry at 105 ° C and fuse at 220 ° –250 ° C (mp 208 ° C), holding at this temperature ca 15 min after crystals are melted. Protect from dust during preparation. Cool in desiccator, remove product from beaker, powder in mortar, dry 1/2 h at 105 ° C, and store in brown glass-stoppered bottle in dark over good desiccant. in 20 mL boiling water containing ca 5 drops NHO 3

Molarity (mol/L) = g AgNO 3

× 1000/mL titer × 169.87

References: JAOAC 25 , 661(1942); 30 , 105, 496(1947).

 2005 AOAC INTERNATIONAL

10/9/2018