88 / 258
1392
Jaudzems:
J
ournal of
AOAC I
nternational
V
ol.
98, N
o.
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
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
.
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
a
1.4 mg/100 g
a
Analytical range, mg/100 g
5–500 mg/100 g
a
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
r
(repeatability), %
≤2
Average RSD
r
= 0.31% (17 products),
range 0.03–1.60%; concentration range evaluated
20–167 mg/100 g RTF
RSD
R
(reproducibility), %
≤4
RSD
IR
(intermediate reproducibility)
Not assessed
Average RSD
R
= 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.
88