© 2013AOAC INTERNATIONAL
Predigest for at least 10 min at room temperature or until
vigorous foaming subsides.
Close MDC vessels and distribute onto microwave carousel to
ensure uniformmicrowave power application on all samples.
(
3
)
Food-grade salt sample preparation
.—Weigh 0.20 ± 0.01 g
food-grade salt into a 100 mL volumetric flask. Add deionized
water and 10 mLHNO
3
. Dissolve salt and dilute to volume with
deionizedwater.
(
b
)
Test portion digestion
.—[
Caution
: Application of
microwave digestion systems involves hot pressurized acid
solutions and concentrated acids. Use fume hood and wear full
personal laboratoryprotective clothing, gloves and appropriate eye
protection (safety glasses) when using glassware and preparing
standards or samples with acid solutions. Follow manufacturer’s
directions for safety risk and safety environment of microwave
systems. Never remove hot vessels from microwave; wait until
they are near room temperature. Keep microwave door closed
while vessels are hot. The door is the primary safety device if a
vessel vents.]
(
1
)
Sample digestion.—
With power setting appropriate toMDC
(maximumpower of 1600W) andMDOmodels (maximumpower
of 600W), andnumber of vessels used, heatMDOvessels at 200±
20°C for 20minor rampMDC temperature from ambient to200±
20°C in15minandholdat 200°C for 25min. (
Note:
Yellowvapors
will be emitted during the hydrolysis inMDO vessels.)
Carefully remove the MDO vessels. Allow the vessels to cool
down to room temperature.
Add 5 mL HCl 35% (w/v) into MDO vessels and heat MDO
vessels at 200± 20°C for 20min.
Table 2011.14B. Interlaboratory study results for copper
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
5.92
NA
h
0.09
1.57
0.29
4.97
0.41
9
NS
g
Dieteticmilk powder 2
6.19
101
0.19
3.06
0.38
6.12
0.50
9
NS
Infant cereal
2.01
NA 0.10
4.98
0.24
11.72
0.81
9
NS
Peanut butter NISTSRM2387
4.98
(4.93)
i
101
0.19
3.84
0.35
7.08
0.56
9
NS
Wheat glutenNISTRM 8418
5.64
(5.94)
i
95
0.13
2.27
0.27
4.77
0.39
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
NA=Not available.
i
Value in parentheses =Certified or reference values.
Table 2011.14C. Interlaboratory study results for iron
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
164.77
97
6.72
4.08
11.25
6.83
0.92
9
NS
g
Dieteticmilk powder 2
83.11
102
2.51
0.02
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 NISTSRM2387 15.65
(16.4)
h
95
0.65
4.17
1.95
12.45
1.18
8
6C
Wheat glutenNISTRM8418
49.29
(54.3)
h
91
0.93
1.89
1.54
3.12
0.35
8
2C
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
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