Methods to be Reviewed by OMB in 2016

1392

Jaudzems:

ournal of

AOAC I

nternational

ol.

98, N

5, 2015

(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

.—Sigma-Aldrich 10220, or equivalent.

D. Solutions

(a)

Nitric acid.—

Minimum 65% p.a. (Merck, or equivalent).

(b)

Standardized AgNO

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

solution, 0.01 M (optional)

.—Into a 1000 mL

volumetric flask, pipette 100 mLAgNO

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

solution, 0.1 M.—

If no ready-to-use

AgNO

standard solution is available, weigh 16.9890 ± 0.0005 g

AgNO

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

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)

LOQ, mg/100 g

5 mg/100 g

1.4 mg/100 g

Analytical range, mg/100 g

5–500 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

RSD

(repeatability), %

≤2

Average RSD

= 0.31% (17 products),

range 0.03–1.60%; concentration range evaluated

20–167 mg/100 g RTF

RSD

(reproducibility), %

≤4

RSD

(intermediate reproducibility)

Not assessed

Average RSD

= 0.54% (17 products);

range 0.09–2.77%; concentration range evaluated

20–167 mg/100 g RTF

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.

Candidates for 2016 Method of the Year

101