OMB Meeting Book - Jan. 11, 2018

(n) Disposable syringe .—3 mL, with handspike and 0.45 μm disposable syringe filter. C. Chemicals and Reagents (a) Water, purified .—>18MΩ (EMD Millipore Corp., Billerica, MA, USA), or equivalent. (b) Sodium chloride (NaCl) .—Certified reference material for titrimetry, ≥99.5%, certified by the Federal Institute for Materials Research and Testing (Berlin, Germany) according to ISO 17025 (Cat. No. 71387; Sigma-Aldrich, St. Louis, MO, USA), or equivalent. (c) Silver nitrate (AgNO 3 ) .—Meets analytical reagent specification of the European Pharmacopoeia (Reag. Ph. Eur.), British Pharmacopoeia, and the United States Pharmacopeia (USP); assay 99.8–100.5% (Cat. No. 10220; Sigma-Aldrich); or equivalent. (d) Potassium ferrocyanide trihydrate [K 4 Fe(CN) 6 · 3H 2 O] .— Grade puriss p.a., American Chemical Society (ACS), International Organization for Standardization (ISO), and Reag. Ph. Eur.; ≥99% (Cat. No. 31524; Sigma-Aldrich); or equivalent. (e) Zinc acetate dihydrate [Zn(CH 3 COO) 2 2H 2 O] .—Grade ACS and puriss p.a., ≥99.0% (Cat. No. 96459; Sigma-Aldrich), or equivalent. (f) Nitric acid (HNO 3 ) .—Minimum 65% puriss p.a. (Cat. No. 100452; Merck, Darmstadt, Germany), or equivalent. (g) Standardized AgNO 3 solution .—0.1 mol/L (0.1 N) Titripur ® grade Reag. Ph. Eur. and USP (Cat. No. 1.09081.1000 or EM3214-1; Merck, Darmstadt, Germany) or ready-to-use standardized titrant prepared according to GB/T 601-2002 (1), or equivalent. (h) Sodium chloride ( NaCl) standardized solution, 0.1 M .—Cat. No. 35616 (Alfa Aesar, Ward Hill, MA, USA), or equivalent. (i) Glacial acetic acid, 100% . — Anhydrous for analysis; EMSURE ® grade ACS, ISO, and Reag. Ph. Eur. (Cat. No. 100063; Merck); or equivalent (j) Potassium nitrate (KNO 3 ) .—For analysis, EMSURE ® grade ISO and Reag. Ph. Eur. (Cat. No. 105063; Merck), or equivalent. (k) Acetone.— For cleaning of the electrode (Cat. No. 010-4; Honeywell, Muskegon, MI, USA), or equivalent. (l) Dimethylpolysiloxane .—Defoaming agent (Cat. No. DMPS2C; Sigma-Aldrich), or equivalent. D. Preparation of Solutions (a) Standardized AgNO 3 solution, 0.1 M. —If ready-to-use AgNO 3 standard solution, C ( c ), is not available, then weigh 16.9890 ± 0.0005 g AgNO 3 previously dried for 2 h at 120 ± 2°C. Dissolve in water and dilute to volume in a 1000 mL volumetric flask. Store in a brown reagent bottle. Note 1 : After preparation, check the titer by titration of 5.0 mLwith exactly 0.1 M NaCl solution. For either commercial or in-house solution, verify the titer on a regular basis. Note 2 : The standardized AgNO 3 solution must be protected from light, and can be stored for up to 2 months. (b) Sodium chloride solution, 0.1 M .—If ready-to-use NaCl standard solution is not available, weigh 5.8440 ± 0.0005 g NaCl, C ( b ), previously dried for 2 h at 110 ± 2°C. Dissolve in water and dilute to volume in a 1000 mL volumetric flask. Note : This solution is stable for up to 1 month. (c) Precipitating solution (Carrez) I .—Weigh 106 g potassium ferrocyanide trihydrate, C ( d ), dissolve in an appropriate amount of water, and transfer to a 1000 mL volumetric flask. Dilute to volume using water. Mix well.

AOAC Official Method 2016.03 Chloride in Milk, Milk Powder, Whey Powder, Infant Formula, and Adult Nutritionals Potentiometric Titration Method First Action 2016 [Applicable to the determination of chloride in milk, milk powder, whey powder, infant formula, and adult nutritionals by potentiometry, with an analytical range of 0.35–1060 mg chloride/100 g reconstituted product or ready-to-feed (RTF) liquids.] Caution : Consult Material Safety Data Sheets for all substances A. Principle Reconstitute powder samples by dissolving 25 g powder sample in 200 g warm water (40°C); RTF products are ready to use as they are. Precipitate proteins by adding precipitation solutions I and II, and then centrifuge. Acidify the supernatant with nitric acid solution. Titrate chloride ions against standardized silver nitrate solution (0.1 M), potentiometrically using a silver electrode to detect the end point. B. Apparatus Common laboratory equipment and, in particular, the following: (a) Analytical balance .—Precision to 0.1 mg. (b) Centrifuge .—Tabletop with rotor for 50 mL conical tubes, capable of operating at ≥12000 × g . (c) Centrifuge tubes .—50 mL, conical, polypropylene. (d) Pipets .—1, 10, 20, 50, and 100 mL, Class Aglass volumetric or automatic (Eppendorf or equivalent). (e) One-mark volumetric flasks .—50, 100, 500, and 1000 mL, glass, Class A. (f) Graduated cylinders .—25, 100, and 500 mL, glass. (g) Autosampler beaker .—e.g., 120 mL, depending on the titrator used. (h) pH Meter/mV meter .—With a scale covering ±700 mV, and a 20 or 25 mL buret (Mettler-Toledo, Columbus, OH, USA), or equivalent. (i) Automatic titrator .—Autosampler (Mettler-Toledo Rondo Tower) and motorized piston buret (Mettler-Toledo T50) with remote-control dispensing and filling (Mettler-Toledo LabX 3.1 software) or the Metrohm 862 Compact Titrosampler with 800 Dosino and 10 mL Exchange Unit (Riverview, FL, USA), or equivalent. Alternatively, a semiautomated (e.g., Metrohm Titrado 905/907, with Metrohm tiamo TM software, or equivalent) or a manual titrator (using a buret with accuracy of 0.01 mL) may be used. (j) Combined ring silver electrode .—e.g., Mettler DM 141 or DMi145-SC, MetrohmAg Titrode No. 6.0430.100S, or equivalent. Alternatively, a silver electrode with reference electrode may be used. (k) Magnetic stirrer .—Heidolph MR 3000 (Schwabach, Germany) or Metrohm 804Ti Stand with 802 Rod Stirrer, or equivalent. (l) Water bath .—Capable of warming water to 40°C, or equivalent. (m) Ultrasonic cleaner .—Model AS2060B (Tianjin Automatic Science Instrument Co. Ltd, Nanyang, China), or equivalent. that are required and considered hazardous. Follow all laboratory safety precautions and wear proper personal protective equipment.

© 2016 AOAC INTERNATIONAL

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