6. AOACSPIFANMethods-2018Awards

88

1392 Jaudzems: J ournal of AOAC I nternational V ol. 98, N o. 5, 2015

Table 2015.08C. Comparison of SLV data with SMPR requirements Parameter SMPR 2014.015

Single-laboratory validation

Matrixes

SLV test matrixes kit (17 samples)

All forms of infant, adult, and/or pediatric formula (powders, RTF liquids, and liquid concentrates)

5 mg/100 g a

1.4 mg/100 g a

LOQ, mg/100 g

5–500 mg/100 g a

Analytical range, mg/100 g

1.4–1060 mg/100 g

Spike recovery, %

95–105

SPIFAN samples (15) were spiked at two levels of chloride on 6 separate days Spike level 1: average recoveries of 101.6% (range 101–103%) Spike level 2: average recovery of 100.6% (range 99–103%)

Bias versus SRM

NIST 1849a informational value = 710 mg/100 g

Value found = 685 mg/100 g, recovery = 97.2%, no bias at 95% confidence level = 0.31% (17 products), range 0.03–1.60%; concentration range evaluated 20–167 mg/100 g RTF Average RSD r

RSD r

(repeatability), %

≤2

RSD R RSD IR

(reproducibility), %

≤4

(intermediate reproducibility) = 0.54% (17 products); range 0.09–2.77%; concentration range evaluated 20–167 mg/100 g RTF a  Concentrations apply to: (a) RTF liquids as is; (b) reconstituted powders (25 g into 200 g water); and (c) liquid concentrates diluted 1:1 by weight. Not assessed Average RSD R

(a)  Analytical balance.— Precision 0.1 mg. (b)  Class A volumetric flasks.— 100 and 1000 mL. (c)  pH meter/mV meter with a scale covering ±700 mV, and buret, 20 or 25 mL.— Mettler-Toledo (Columbus, OH) or equivalent. (d)  Automatic titrator. —Autosampler, motorized piston buret, with remote-control dispensing and filling (Mettler Toledo T50 Rondo Tower autosampler, Mettler LabX 3.1 software, or equivalent). (e)  Combined ring silver electrode.— e.g., Mettler Toledo DM 141 or DMi145-SC, or equivalent; alternatively, a silver electrode with reference electrode can be used. (f)  Magnetic stirrer.— Heidolph MR 3000 or equivalent (Sigma-Aldrich, St. Louis, MO). (g)  Water bath .—Capable of warming water to 40°C. (h)  Laboratory oven.— Capable of heating to 120°C. (i)  Pipets (1, 20, 50, and 100 mL) .—Class Aglass volumetric or automatic (Eppendorf or equivalent). (j)  Buret.— 10 mL. C. Chemicals and Reagents (a)  Acetone.— p.a. (Merck, Darmstadt, Germany, or equivalent). (b)  Water, purified.— Greater than 18MΩ (EMD Millipore Corp., Billerica, MA, or equivalent). (c)  Sodium chloride (NaCl) , crystal .—Fluka 71387 (Sigma-Aldrich, or equivalent). (d)  AgNO 3 .—Sigma-Aldrich 10220, or equivalent. D. Solutions (a)  Nitric acid.— Minimum 65% p.a. (Merck, or equivalent). (b)  Standardized AgNO 3 solution, 0.1 M.— Merck TitriPUR, or equivalent. (c)  NaCl solution, 0.1 M .—Alfa Aesar (Ward Hill, MA), or equivalent.

E. Preparation of Solutions (a)  Dilute nitric acid solution, 2% (v/v).— Into a 1000 mL volumetric flask, add about 800 mL water. Carefully pipette 20 mL concentrated nitric acid (65%). Make up to 1000 mL with water. Stopper the volumetric flask and mix well. (b)  AgNO 3 solution, 0.01 M (optional) .—Into a 1000 mL volumetric flask, pipette 100 mLAgNO 3 solution, 0.1 M. Make up to the mark with water. Check the titer by titration of 20 mL exactly 0.01 M NaCl solution. (c)  NaCl solution, 0.01 M (optional) .—Into a 1000 mL volumetric flask pipette 100 mL NaCl solution, 0.1 M. Make up to the mark with water. (d)  Standardized AgNO 3 solution, 0.1 M.— If no ready-to-use AgNO 3 standard solution is available, weigh 16.9890 ± 0.0005 g AgNO 3 previously dried for 2 h at 120 ± 2°C. Dissolve in water and make up to the mark in a 1000 mL volumetric flask. Check the titer by titration of 20 mL exactly 0.1 M NaCl solution. (e)  NaCl solution, 0.1 M .—If no ready-to-use NaCl standard solution is available, weigh 5.8440 ± 0.0005 g NaCl, previously dried for 2 h at 110 ± 2°C. Dissolve in water and make up to the mark in a 1000 mL volumetric flask. F. Sample Preparation Milk product, infant formula, and adult/pediatric nutritional .—Mix well to ensure that sample is homogeneous. Powder samples were reconstituted by dissolving 25 g powder sample in 200 mL warm water (40°C). G. Instrument Operating Conditions Connect the combined silver electrode to the automated titration apparatus according to the manufacturer’s instructions. Ensure that the titration vessels are correctly placed on the autosampler and there are enough reagents, both 2% (v/v) nitric acid and 0.1 MAgNO 3 .