180
P
oitevin
: J
ournalof
AOAC I
nternational
V
ol
. 95, N
o
. 1, 2012
and collect the remaining filtrate for analysis.
Note
:Membrane
discfilters (0.45µm)arenot recommended, as theyaregenerally
notmetal-free.
Transfer to polyethylene containers within 2 h. Dilute
samples that are above the standard curve range or have total
content of minerals higher than 1000 mg/L with H
2
O.
Note
:
Final dilutions require the addition of appropriate amounts of
HNO
3
for MDC digests (or appropriate amounts of combined
acids forMDO) tomaintain the proportion of 10% (v/v)HNO
3
(15%, v/v, combined acids and hydrogen peroxide) in the final
solution to be analyzed.
(
2
)
Digestion vessel decontamination.—
Decontaminate the
usedMDC digestion vessels with 5 mLHNO
3
according to a
program close to that displayed in
b
(
1
). Wash theMDO glass
volumetric flasks in a laboratory washing machine or soak
overnight in a water bath with HNO
3
30% (v/v).
Rinse with
H
2
O toavoidorminimize riskof ironcontamination.DryMDC
vessels at 60°C in drying oven for 1 h.
Detection
E. Principle
Digested test solution or an appropriate dilution is presented
to the ICP-OES instrument, which is calibrated with acid(s)-
Table 2011.14C. Interlaboratory study results for iron
Matrix
Mean, mg/kg Rec.,%S
r
,mg/kg
a
RSD
r
,%
b
S
R
, mg/kg
c
RSD
R
,%
d
HorRat No. of labs
e
Outlier labs
f
Chocolatemilk powder
164.77
97
6.72
4.08
11.25
6.83
0.92
9
NS
g
Dieteticmilk powder 2
83.11
102 2.51
3.02
4.62
5.56
0.68
9
NS
Infant cereal
75.18
94
1.36
1.81
3.32
4.42
0.53
9
NS
Peanut butter
NISTSRM 2387
15.65 (16.4)
h
95
0.65
4.17
1.95
12.45
1.18
8
6–C
Wheat gluten
NISTRM 8418
49.29 (54.3)
h
91
0.93
1.89
1.54
3.12
0.35
8
9–C
a
S
r
=SD for repeatability (within laboratory).
b
RSD
r
=RSD for repeatability.
c
S
R
=SD for reproducibility (among laboratories).
d
RSD
R
=RSD for reproducibility.
e
Reporting laboratoriesminus outliers.
f
C=Cochran outlier.
g
NS=Not significant.
h
Certifiedor reference values.
Table 2011.14D. Interlaboratory study results for potassium
Matrix
Mean, mg/kg Rec.,% S
r
,mg/kg
a
RSD
r
,%
b
S
R
, mg/kg
c
RSD
R
,%
d
HorRat No. of labs
e
Outlier labs
f
Chocolatemilk powder
8996.74
99 135.82 1.51 208.98 2.32 0.57
9
NS
g
Dieteticmilk powder 2
6443.79
100 65.17 1.01 130.04 2.02 0.47
9
NS
Infant cereal
6438.19
99 119.83 1.86 135.78 2.11 0.49
8
6–SG
Peanut butter
NISTSRM 2387
6200.24 (6070)
h
102 148.84 2.40 187.59 3.03 0.70
9
NS
Wheat gluten
NISTRM 8418
411.08 (472)
h
87
10.19
2.48
31.31
7.62
1.18
9
NS
a
S
r
=SD for repeatability (within laboratory).
b
RSD
r
=RSD for repeatability.
c
S
R
=SD for reproducibility (among laboratories).
d
RSD
R
=RSD for reproducibility.
e
Reporting laboratoriesminus outliers.
f
SG=SingleGrubbs outlier.
g
NS=Not significant.
h
Certifiedor reference values.
MTE-01
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