bufferandsamplepumptubes(i.e.,orange/white,0.64mmid)
using automatic addition.
SamplePreparationandDigestion
(
a
)
Test sample preparation
.—Homogenize the test
sample (e.g., serving size or declared labeled size) by either
grinding as fine as possible using a mixer to obtain a fine
powder and/or by preparing a slurry with H
2
O: weigh 10
±0.1 g test sample, and put into a 100mLErlenmeyer flask;
add 90±0.1 gH
2
O, andmixwell with stopper (
Note
:Water
can be preheated at 50 C for a better homogenization of
samples, e.g., infant cereals and fortifiedmilkpowders).
(
b
)
Test portionpreparation for closed-vesselmicrowave
digestion (SLV, MD1, MD3, and MD4 ruggedness
tests
).—Accurately weigh 0.50 ± 0.01 g test portion (or
samplemass in thepreparedslurry) intodigestionvessel.Use
eitherweighingpaper insert to line thevesselwallsorPasteur
pipet during sample transfer tokeep sample fromadhering to
sides of vessel. Fluid samples or test portion fromslurry test
sample may be weighed directly after mixing. Add 5.0 ±
0.1 mL analytical grade HNO
3
, loosely cap vessels without
sealing, and predigest at room temperature until vigorous
foaming subsides. Close vessels and place in CEM Mars
Xpress microwave or in other closed-vessel microwave
systems.
(
c
)
Test portion preparation for open-vessel microwave
digestion (MD2 ruggedness test)
.—Accurately weigh 1.0 ±
0.01gtestportion(orsamplemass intheslurry) intoa100mL
volumetric flask. Carefully add 5mLHNO
3
and then 5mL
H
2
O
2
. Allow the sample to stand for at least 10min at room
temperature. Distribute the volumetric flasks onto the
open-vessel microwave carousel to ensure homogeneous
microwave power applicationon all samples.
(
d
)
Sample digestion for closed-vessel microwave
digestion (SLV, MD1, MD3, and MD4 ruggedness
tests)
.—Digest sample according to a ramp program as
follows: Conditions:
Stage 1
.—Power, expressed as
maximumpower (1600watts for CEMMarsXpress system)
= 75%; ramp time, 5 min; 120 C; hold time, 5 min.
Stage 2
.—Power, 75%; ramp time, 5min; 200 C; hold time,
25min.Thencool vessels, vent, and transferdigests to50mL
volumetric flasks, dilute to volume with H
2
O, and mix. A
digestion is judged completewhen clear-to-yellowanalytical
solutions are produced. Filter the digested solution using an
ashless filter paper for turbid samples containing fat,
discarding the first 20 mL of filtrate and collecting the
remaining filtrate for analysis. [
Note
: Membrane disc filters
(0.45 m) are not recommended as they are generally not
metal free.] Transfer to polyethylene containers within 2 h.
Dilute with H
2
O the samples that are found to be above the
standardcurve range, or have total content ofmineralshigher
than 1000 mg/L. Final dilutions require addition of
appropriate amounts of HNO
3
tomaintain the proportion of
10%(v/v)HNO
3
in the final solution tobe analyzed.
(
e
)
Sampledigestion foropen-vesselmicrowavedigestion
(MD2 ruggedness test)
.—Digest sample according to an
appropriate power programclose to that described inTable 3
for a CEMMDS 2000 systemdepending on the number of
distributedflasks.This first steprequires20minheating time.
Yellow vapors will be emitted during the hydrolysis.
Carefully remove the flasks from the microwave system.
Allow the flasks to cool to room temperature and add 5mL
HCl35%(w/v).Heat theflasks foranadditional10minusing
the same programin themicrowave system.Allowthe flasks
to cool to room temperature. Transfer digests to 100 mL
volumetric flasks, dilute tovolumewithH
2
O, andmix. Filter
andprepare thedigestedsolutionbeforeanalysis asdescribed
for closed-vesselmicrowavedigestion in (
d
) butmaintain the
proportion of 15%(v/v) combined acids in the final solution
tobe analyzed.
(
f
)
Digestion vessel decontamination for closed-vessel
microwavedigestion(SLV,MD1,MD3,andMD4ruggedness
tests).
—Conditions:
Step 1
.—Power, express in % of
maximumpower (1600watts for CEMMarsXpress system)
= 75%; ramp time, 5 min; 180 C; hold time, 5 min.
Decontaminate useddigestionvesselswith5mLHNO
3
for a
CEMMarsXpress systemand rinsewithH
2
O.Dryvessels at
60 C indryingoven for 1h.
1488
P
OITEVINETAL.
: J
OURNALOF
AOACI
NTERNATIONAL
V
OL
. 92,N
O
. 5, 2009
Table 5. Recommendedandalternate ICPanalytical
linesused forSLVandRT
Element lines, nm
Internal standard lines, nm
Ca II
a
317.933
In I
303.936
Ca II
b
317.933
Y II
371.028
Cu I
a
324.754
In I
303.936
Cu I
b
324.754
Y II
371.028
Cu I
b
327.395
In I
303.936
Cu I
b
327.395
Y II
371.028
Fe II
a
259.94
Sr II
338.071
Fe II
b
259.94
Y II
371.028
Fe II
b
259.94
Cr II
283.563
K I
a
766.491
Sr I
460.733
Mg I
a
285.213
In I
303.936
Mg I
b
285.213
Y II
371.028
Mg II
a
279.078
In I
303.936
Mn II
b
257.61
Sr II
338.071
Mn II
b
257.61
Sr I
460.733
Mn II
b
257.61
Y II
371.028
Na I
a
589.592
Sr I
460.733
P I
a
213.618
In I
303.936
P I
b
178.222
Sr I
460.733
P I
b
178.222
Y II
371.028
Zn I
a
213.857
Sr II
338.071
Zn I
b
213.857
Sr I
460.733
Zn I
b
213.857
Y II
371.028
a
Recommended lines for ICP-AESanalysis.
b
Alternateconfirmatory lines for ICP-AESanalysis.
MTE-01
FORWORKINGGROUP/ERPUSEONLY
DONOTDISTRIBUTE
