P
oitevin
:
J
ournalof
AOAC I
nternational
V
ol
.
95, N
o
. 1, 2012
179
when using glassware and preparing standards or sampleswith
acid solutions. Followmanufacturer’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 15min and hold at
200°C for 25min.
Note:
Yellow vapors will be emitted during
the hydrolysis inMDO vessels.
Carefully remove theMDO 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 20min.
Cool vessels to room temperature before venting (MDC
vessels).Transfer theMDCdigests to50mL(100mLforMDO)
volumetric flasks. Dilute to volume with H
2
O, and mix.
Note
:
Adigestion is judged completewhen clear to yellow analytical
solutions are produced.
Filter the digested solution using an ashless filter paper for
turbid samples containing fat. Discard the first 20mLof 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
Chocolatemilk powder
9732.17
99 152.10 1.56 264.03
2.71
0.68
9
NS
g
Dieteticmilk 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
NISTSRM 2387
409.90 (411)
h
100 13.37 3.26
28.20
6.88
1.06
9
NS
Wheat gluten
NISTRM 8418
367.56 (369)
h
100
3.51
0.95
12.90
3.51
0.53
7
2, 4C
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 2011.14B. 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
Chocolatemilk powder
5.92
NA
f
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
NISTSRM 2387
4.98 (4.93)
h
101
0.19 3.84
0.35
7.08
0.56
9
NS
Wheat gluten
NISTRM 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 laboratoriesminus outliers.
f
NA=Not available.
g
NS=Not significant.
h
Certifiedor reference values.
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