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P
oitevin
:
J
ournal of
AOAC I
nternational
V
ol
.
95, N
o
. 1, 2012
179
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
to MDC (maximum power of 1600 W) and MDO models
(maximum power of 600 W), and number of vessels used,
heat MDO vessels at 200 ± 20°C for 20 min or ramp MDC
temperature from ambient to 200 ± 20°C in 15 min and hold at
200°C for 25 min.
Note:
Yellow vapors will be emitted during
the hydrolysis in MDO vessels.
Carefully remove the MDO vessels, and allow them to cool
to room temperature.
Add 5 mL HCl 35% (w/v) into MDO
vessels and heat at 200 ± 20°C for 20 min.
Cool vessels to room temperature before venting (MDC
vessels). Transfer the MDC digests to 50 mL (100 mL for MDO)
volumetric flasks. Dilute to volume with H
2
O, and mix.
Note
:
A digestion is judged complete when clear to yellow analytical
solutions are produced.
Filter the digested solution using an ashless filter paper for
turbid samples containing fat. Discard the first 20 mL of filtrate
Table 2011.14A. Interlaboratory study results for calcium
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
Chocolate milk powder
9732.17
99 152.10 1.56 264.03
2.71
0.68
9
NS
g
Dietetic milk powder 2
5678.58
98 75.93 1.34 184.11
3.24
0.74
9
NS
Infant cereal
5983.54 100 210.58 3.52 251.67
4.21
0.97
9
NS
Peanut butter
NIST SRM 2387
409.90 (411)
h
100 13.37 3.26
28.20
6.88
1.06
9
NS
Wheat gluten
NIST RM 8418
367.56 (369)
h
100
3.51
0.95
12.90
3.51
0.53
7
2, 4 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 laboratories minus outliers.
f
C = Cochran outlier.
g
NS = Not significant.
h
Certified or reference values.
Table 2011.14B. Interlaboratory study results for copper
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
Chocolate milk powder
5.92
NA
f
0.09 1.57
0.29
4.97
0.41
9
NS
g
Dietetic milk 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
NIST SRM 2387
4.98 (4.93)
h
101
0.19 3.84
0.35
7.08
0.56
9
NS
Wheat gluten
NIST RM 8418
5.64 (5.94)
h
95
0.13
2.27
0.27
4.77
0.39
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 laboratories minus outliers.
f
NA = Not available.
g
NS = Not significant.
h
Certified or reference values.
2011.14 (MTE-01) MLT
FOR ERP USE ONLY
DO NOT DISTRIBUTE