AOAC Final Action Methods in 2018

(m) Ultrasonic cleaner .—Tianjin Auto Science AS2060B or equivalent. (n) Disposable syringe .—3 mL, with handspike and 0.45 μm disposable syringe filter. ( o )  Blender .—Capable to hold and blend 100 mL volume. C. Chemicals and Reagents (a) Water .—Purified, Type I (EMD Millipore Corp., Billerica, MA, USA), or equivalent. (b) Sodium chloride (NaCl) .—Purity ≥99.5%, Certified Reference Material for titrimetry, Sigma-Aldrich Part. No. 71387, or equivalent. (c) Silver nitrate (AgNO 3 ) .—Meets analytical specification of European Pharmacopoeia (Ph. Eur.), British Pharmacopoeia (BP), and United States Pharmacopeia (USP); assay 99.8–100.5%, Sigma-Aldrich Part. No. 10220, or equivalent. (d) Potassium ferrocyanide trihydrate [K 4 Fe(CN) 6 · 3H 2 O] .— Puriss, p.a., American Chemical Society (ACS), International Organization for Standardization (ISO), and Ph. Eur. reagents; ≥99%, Sigma-Aldrich Part. No. 31524 or equivalent. (e) Zinc acetate dihydrate [Zn(CH 3 COO) 2 · 2H 2 O] .—ACS reagent, puriss p.a., ≥99.0%, Sigma-Aldrich Part. No. 96459, or equivalent. (f) Nitric acid (HNO 3 ) .—Minimum 65% puriss p.a., Merck No. 100452, or equivalent. (g) Standardized AgNO 3 solution .—Substance concentration c = 0.1 mol/L, Titripur ® Ph. Eur. and USP reagents No. 1.09081.1000 or EM3214-1, or ready-to-use standardized titrant prepared according to GB/T 601 (2), or equivalent. (h) Sodium chloride ( NaCl) standardized solution .— c = 0.1 mol/L, Alfa Aesar Part No. 35616 (Ward Hill, MA, USA), or equivalent. (i) Glacial acetic acid, 100% . — Anhydrous for analysis; EMSURE ® ACS, ISO, and Ph. Eur. reagents, Merck Part No. 100063 or equivalent. (j) Potassium nitrate (KNO 3 ) .—For analysis, EMSURE ® ISO and Ph. Eur. reagents, Merck Part No. 105063, or equivalent. (k) Acetone.— For cleaning of the electrode (No. 010-4; Honeywell, Muskegon, MI, USA, or equivalent). (l) Dimethylpolysiloxane .—Defoaming agent (Part No. DMPS2C; Sigma-Aldrich, or equivalent). D. Solutions (a) Standardized AgNO 3 solution, c = 0.1 mol/L. —If ready-to-use AgNO 3 standard solution, C ( g ), is not available, then weigh 16.9890 ± 0.0005 g AgNO 3 , C ( c ), 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. After preparation, check the titer by titration of 5.0 mL with exactly 0.1 mol/L NaCl, C ( h ) or D ( b ), solution. For either commercial or in-house solution, verify the titer on a regular basis following equation 1 or 2 in Calculations section. If outside 0.095– 0.105 mol/L, then investigate. Store standardized AgNO 3 solution protected from light for up to 2 months. (b) Sodium chloride solution, c= 0.1 mol/L .—If ready-to- use NaCl, C ( h ), 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. 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

AOAC Official Method 2016.03 Chloride in Milk, Milk Powder, Whey Powder, Infant Formula, and Adult Nutritionals Potentiometric Titration Method

First Action 2016 Final Action 2018 Codex-Adopted AOAC–ISO/IDF Method *

[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

that are required and considered hazardous. Follow all laboratory safety precautions and wear proper personal protective equipment.

A. Principle The method specifies one method [combined from 2015.07 ( see 50.11.01) and 2015.08 ( see 50.11.02)] for the determination of chloride in milk, milk powder, infant formula, and adult nutritionals by potentiometry, with an analytical range of 0.35–1060 mg chloride/100 g reconstituted product, or RTF liquids. Reconstitute powder samples by dissolving 25 g powder sample in 200 g warm water (40°C); RTF products are used as- is. Precipitate proteins by adding precipitation reagents I and II and centrifuge. Acidify the supernatant with nitric acid solution. Titrate chloride ions against standardized silver nitrate solution (0.1 mol/L) potentiometrically using a silver electrode to detect the end point. B. Apparatus Common laboratory equipment and, in particular, the following: (a) Analytical balance .—Precision 0.01 and 0.1 mg. (b) Centrifuge .—Table-top 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, glass, volumetric or automatic, Class A in accordance with ISO 1042:1998 (1). (e) One-mark volumetric flasks .—50, 100, 500, and 1000 mL, glass, Class A in accordance with ISO 1042:1998 (1). (f) Graduated cylinders .—25, 100, and 500 mL, glass. (g) Autosampler beaker .—Depending on the titrator used, e.g., 120 mL. (h) pH meter or mV meter .—With a scale covering ±700 mV, and a 20 or 25 mL buret. (i) Automatic titrator .—Autosampler, motorized piston buret, with remote control dispensing and filling. Mettler T50, Rondo Tower autosampler, MettlerLabX 3.1 software or Metrohm 862 Compact Titrosampler, 800 Dosino, 10 mL Exchange Unit, or equivalent. Alternatively a semiautomated (e.g., MetrohmTitrado 905/907, with MetrohmTiamo™ software) or equivalent. Amanual titrator (using a buret with accuracy of 0.01 mL) may also be used. (j) Combined ring silver electrode .—Mettler DM 141 or DMi145-SC, Metrohm Ag Titrode 6.0430.100, or equivalent. Alternatively, a silver electrode with reference electrode. (k) Magnetic stirrer .—Heidolph MR 3000 or Metrohm 804Ti Stand with 802 Rod Stirrer, or equivalent. (l) Water bath .—Labotech DWM 16, or equivalent.

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