optimization or training, operating below the limit of
determination, or an unsatisfactorymethod. It is nowone of
the acceptability criteria for many of the recently adopted
chemical methods analysis of AOAC INTERNATIONAL,
the European Union, and other European organizations
dealingwith food analysis (33).
(
j
)
Ruggedness
.—Three replicate test portions (
r
= 3)
were collected from each of the six (
n
= 6) different food
samplespopulating threeof theninefood trianglesectors, and
thenweredigestedusingdifferent closed-vessel (MD1,MD3,
and MD4) and open-vessel (MD2) microwave digestion
systems(Table1).Triplicateswereanalyzedfor8days(
d
=8)
corresponding to nine series (i.e., nine elements) of 144 data
(
n r d
=144), andusingdifferent ICPequipmentwith the
recommended lines (except the use of alternate
2
MnII and
2
Zn I alternate lines for theMD4 test) according to adapted
ICP operating conditions used for SLVwith addition of ion
buffer Cs 0.1%(w/v). Recoverymedian values, SD
r
(within
day), SD
iR
(between day), and HorRat values were
determined. Accuracywas statistically evaluated.
RingTrial
(
a
)
Designof thestudy
.—Fivematerials that cover fourof
the nine sectors of AOAC food triangle (Table 2) were
proposed for testing the proposed ICP-AES method for
determining the nine elements of interest in food matrixes
aftermicrowave digestion through an internal RT.
(
b
)
Study material
.—Five materials were samples of
existingNISTSRM2387 (peanut butter) andNISTRM8418
(wheatgluten), and three in-house referencesamplesof infant
cerealswithmilkpowder, chocolatemilkpowder, anddietetic
milk powder 2 (DMP2). The three in-house reference
materials were validated through Nestlé proficiency tests
performed by a significant number of internal and external
laboratories (between 12 and 45 depending on element and
materials analyzed). Their reference values and associated
SD
R
valueswere calculatedusing robust statistics (28).
(
c
)
Protocol
.—Three lots of each NIST material were
simply remixed inanamber container and sampleportions of
minimum10 gwere then extracted fromrandomlocations in
the container using a small weighing spatula and transferred
into numbered amber PVC100mLboxes (Greiner Bio-one,
Frickenhausen, Germany) for distribution to participants.
Sample portions of minimum 10 g were extracted from
random locations in each original
P
-test container of the
three in-house references using a small weighing spatula and
transferredintonumberedamberPVC100mLboxes(Greiner
Bio-one) for distribution to participants. One set of five
numbered samples, including five amber 100 mL flasks
containing 10 g materials, was mailed to nine collaborators
whovolunteered toparticipate in this study.
(
d
)
Stock standard solution
.—Prepareworking standards
either from a multistandard commercial stock standard
solution (equivalent to that described for SLV, MD1, and
MD2 tests) or from an intermediate stock standard solution
previously preparedwith ICP-grade individual element 1000
and10000mg/Lsolutions.
(
e
)
Intermediate stock standard solution
.—(Composition
of the intermediatestandardsolution, inmg/L:Ca=1500;Cu
=10;Fe=50;K=2000;Mg=500;Mn=0.25;Na=1000;P=
1000; Zn =20.) Add into a 500mLvolumetric flask, 75mL
calcium10 000mg/L, 5mL copper 1000mg/L, 25mL iron
1000 mg/L, 100 mL potassium, 25 mL magnesium
10000 mg/L, 0.125 mL manganese 1000 mg/L, 50 mL
sodium10 000mg/L, 50mL phosphorus 10 000mg/L, and
10mLzinc1000mg/L.Add10mLof analytical gradeHNO
3
anddilute tovolumewithH
2
O.
(
f
)
Working standard solutions
.—Standards prepared
from intermediate stock standard solution are designed to
have the same acid concentration as digested test solutions.
(
1
)
Std6
.—Pipet15.0mLintermediatestandardsolutionintoa
100mLacid-washedvolumetric flask. Add10mLanalytical
gradeHNO
3
, dilute tovolumewithH
2
O,mix, and transfer to
acid-washed polypropylene bottle. (
2
)
Std5
.—Pipet 10.0mL
intermediate standard solution into a 100 mL acid-washed
volumetric flask.Add10mLanalytical gradeHNO
3
, dilute to
volume with H
2
O, mix, and transfer to acid-washed
polypropylene bottle. (
3
)
Std4
.—Pipet 5.0 mL intermediate
standardsolutionintoa100mLacid-washedvolumetricflask.
Add 10 mL analytical grade HNO
3
, dilute to volume with
H
2
O, mix, and transfer to acid-washed polypropylene bottle.
(
4
)
Std3
.—Pipet 2.0mL intermediate standard solution into a
100mLacid-washedvolumetric flask. Add10mLanalytical
gradeHNO
3
, dilute tovolumewithH
2
O,mix, and transfer to
acid-washed polypropylene bottle. (
5
)
Std2
.—Pipet 1.0 mL
intermediate standard solution into a 100 mL acid-washed
volumetric flask.Add10mLanalytical gradeHNO
3
, dilute to
P
OITEVINETAL.
: J
OURNALOF
AOACI
NTERNATIONAL
V
OL
. 92,N
O
. 5, 2009
1493
Table 10. Median recovery (%) andstandarddeviations
(%) byelement and for all elements ineight food-grade
saltsusing recommended lines
Recovery,%
b
Spikedelement
Concn,mg/L
a
Without Cs
c
WithCs1%w/v
d
Calcium
60
93±4
101±4
Copper
0.4
92±3
105±4
Iron
2
92±3
101±4
Potassium
80
117±18
105±5
Magnesium
20
95±5
102±6
Manganese
0.01
95±7
105±6
Sodium
40
110±14
103±5
Phosphorus
40
90±7
102±4
Zinc
0.8
91±7
103±6
All elements
e
0.01–60
94±9
103±5
a
Concentrationof spikedelement insalt solution.
b
Averageof spikedelement recoveries inall food-gradesalts
solutions.
c
Recoveryvaluewithout Cs ionbuffer addition.
d
RecoveryvaluewithCs ionbuffer 1%(w/v) addition.
e
Medianof all spikedelements recoveries inall food-gradesalts.
MTE-01
FORWORKINGGROUP/ERPUSEONLY
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