© 2013AOAC INTERNATIONAL
(
2
)
Digestion vessel decontamination
.—Decontaminate the
usedMDC vesselswith 5mLHNO
3
according to a program close
to that in
b
(
1
).
Wash theMDO glass volumetric flasks in a laboratorywashing
machine or soak overnight in awater bathwithHNO
3
(30%, v/v).
RinsewithH
2
O toavoidor tominimizeriskof 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 inductively coupled plasma-optical emission spectrometry
(ICP-OES) instrument. The instrument is calibrated with acid(s)
matched standardcalibrant solutions.An ionizationbuffer (cesium)
and internal standard(s) (chromium, indium, strontium, and
yttrium) are used with or without appropriate in-line addition to
Cool vessels to room temperature before venting (MDC vessels).
Transfer theMDC digests to 50mL (100mL forMDO) volumetric
flasks.Dilute tovolumewithH
2
Oandmix. (
Note
:Adigestion is judged
completewhenclear toyellowanalytical solutions areproduced.)
Filter the digested solution using an ashless filter paper for turbid
samples containing fat. Discard the first 20 mL filtrate and collect
the remainingfiltrate for analysis. [
Note
:Membranediscfilters (0.45
μm) arenot recommended as they aregenerallynotmetal-free.]
Transfer to polyethylene containerswithin 2 h.
Dilute the samples that are found to be above the standard curve
range or have total content of minerals higher than 1000 mg/L
withH
2
O. [
Note
: Final dilutions require the additionof 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.]
Table 2011.14D. Interlaboratory study results for potassium
Matrix
Mean, mg/kg Rec.,% S
r
a
RSD
r
b
,% S
R
c
, ng/g 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
6SG
Peanut butter NISTSRM2387 6200.24
(6070)
h
102 148.84 2.40
187.59
3.03
0.70
9
NS
Wheat glutenNISTRM 8418
411.08
(472)
h
87
10.19
2.48
31.31
7.62
1.18
9
NS
a
S
r
=Standarddeviation for repeatability (within laboratory).
b
RSD
r
=
Relative standard deviation for repeatability.
c
S
R
=Standarddeviation for reproducibility (among laboratories).
d
RSD
R
=Relative standard deviation for reproducibility.
e
Reporting laboratoriesminus outliers.
f
C=Cochran outlier; SG=SingleGrubbs outlier; DG=DoubleGrubbs outlier.
g
NS=Not significant.
h
Value in parentheses =Certified or reference values.
Table 2011.14E. Interlaboratory study results formagnesium
Matrix
Mean, mg/kg Rec.,% S
r
a
RSD
r
b
,% S
R
c
, ng/g RSD
R
d
,% HorRat
No. of labs
e
Outlier labs
f
Chocolatemilk powder
1746.74
98
38.46
2.20
51.03
2.92
0.56
8
2SG
Dieteticmilk powder 2
439.31
99
5.57
1.27
13.37
3.04
0.48
9
NS
g
Infant cereal
859.48
98
33.62
3.91
35.38
4.12
0.71
7
2, 6DG
Peanut butter NISTSRM2387 1714.02
(1680)
h
102 56.83
3.32
73.68
4.30
0.82
8
2SG
Wheat glutenNISTRM 8418
482.05
(510)
h
95
8.52
1.77
16.53
3.43
0.54
9
NS
a
S
r
=Standarddeviation for repeatability (within laboratory).
b
RSD
r
=
Relative standard deviation for repeatability.
c
S
R
=Standarddeviation for reproducibility (among laboratories).
d
RSD
R
=Relative standard deviation for reproducibility.
e
Reporting laboratoriesminus outliers.
f
C=Cochran outlier; SG=SingleGrubbs outlier; DG=DoubleGrubbs outlier.
g
NS=Not significant.
h
Value in parentheses =Certified or reference values.
MTE-01
FORWORKINGGROUP/ERPUSEONLY
DONOTDISTRIBUTE
