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© 2015 AOAC INTERNATIONAL
(
b
)
AgNO
3
solution, 0.01 M (optional)
.—Into a 1000 mL
volumetric flask, pipet 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 pipet 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 M
AgNO
3
.
Table 2015.08B. Recovery results of spiking experiments for chloride
+ 50% of native value
+ 100% of native value
Matrix
Native chloride, mg/100 g Average, % RSD, % Average, % RSD, %
SRM NIST 1849a
68.5
104.0
2.8
103.0
1.3
Child formula powder
46.1
102.0
2.1
100.0
1.5
Infant elemental powder
36.8
101.0
1.5
101.0
1.5
Infant formula RTF, milk based (SPIFAN blank milk formula)
20.0
103.0
1.2
101.0
1.1
Adult nutritional powder, milk protein based
36.4
101.0
1.2
100.0
0.7
Infant formula powder partially hydrolyzed, milk based
42.4
101.0
1.0
100.0
1.8
Infant formula powder partially hydrolyzed, soy based
46.2
102.0
1.4
100.0
1.5
Adult nutritional powder low fat
40.3
102.0
1.6
101.0
1.8
Child formula powder
38.6
101.0
1.5
100.0
1.3
Infant elemental powder
39.3
100.0
1.9
101.0
1.2
Infant formula powder, milk based
46.5
100.0
0.5
100.0
0.9
Infant formula powder, soy based
56.1
101.0
1.2
100.0
0.4
Infant formula RTF, milk based (SPIFAN control milk formula)
44.2
103.0
3.2
99.0
1.0
Adult nutritional RTF, high protein
154.5
101.0
0.2
100.0
0.5
Adult nutritional RTF, high fat
162.2
102.0
1.6
103.0
1.9
Table 2015.08C. Comparison of SLV data with SMPR
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.
Candidates for 2016 Method of the Year
97