6. AOACSPIFANMethods-2018Awards

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1114 J audzems : J ournal of AOAC I nternational V ol . 99, N o . 4, 2016

(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), 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 10mLExchangeUnit (Riverview, FL), 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, Metrohm Ag 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. (n) Disposable syringe .—3 mL, with handspike and 0.45 μm disposable syringe filter. (a) Water, purified .—Greater than 18MΩ (EMD Millipore Corp., Billerica, MA), 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), 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 (4), or equivalent. (h) Sodium chloride ( NaCl) standardized solution, 0.1 M .— Cat. No. 35616 (Alfa Aesar, Ward Hill, MA), or equivalent. C. Chemicals and Reagents

(i) Glacial acetic acid, 100% . — Anhydrous for analysis; EMSURE ® grade ACS, ISO, and Reag. Ph. Eur. (Cat. No. ) .—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), or equivalent. (l) Dimethylpolysiloxane .—Defoaming agent (Cat. No. DMPS2C; Sigma-Aldrich), or equivalent. 100063; Merck); or equivalent (j) Potassium nitrate (KNO 3 standard solution [ C ( c )] is not available, then weigh 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. (d) Precipitating solution (Carrez) II .—Weigh 220 g zinc acetate dihydrate [ C ( e )] and transfer to a 1000 mL volumetric flask. Dissolve with an appropriate amount of water and add 30 mL glacial acetic acid [ C ( i )]. Dilute to volume using water. Mix well. (e) Nitric acid solution .—With care, add 100 mL concentrated nitric acid [ C ( f )] to 300 mL water. Mix well. (f) Wash solution .—According to autosampler/titrator manufacturer’s instructions [e.g., acetone or nitric acid solution ( see e , above)], or other. (g) AgNO 3 solution, 0.025M (optional) .—Into a 1000 mL volumetric flask, pipet 250 mL 0.1 M AgNO 3 solution [ C ( g ) or D ( a )]. Dilute to volume with water. Note : Prepare freshly before use, and then check the titer by titration of 25 mL against 0.025 M NaCl solution. (h) NaCl solution, 0.025M (optional) .—Into a 100 mL volumetric flask, pipet 25 mL 0.1 M NaCl solution [ D ( b )]. Dilute to volume with water. Note : Prepare freshly before use. (i) KNO 3 solution, 1 M. —Weigh 10.11 g potassium nitrate [ C ( j )] into a 100 mL volumetric flask. Add about 80 mLwater and place the flask in an ultrasonic cleaner [ B ( m )] to dissolve with ultrasound and heating until dissolved thoroughly. Cool down 16.9890 ± 0.0005 g AgNO 3 D. Preparation of Solutions (a) Standardized AgNO 3 solution, 0.1 M. —If ready-to-use AgNO 3