© 2013AOAC INTERNATIONAL
AOACOfficial Method 2011.14
Calcium, Copper, Iron, Magnesium, Manganese,
Potassium, Phosphorus, Sodium, andZinc
inFortifiedFoodProducts
MicrowaveDigestion and
InductivelyCoupledPlasma-Optical EmissionSpectrometry
FirstAction2011
FinalAction2013
(Applicable to analysis of calcium, copper, iron, potassium,
magnesium, manganese, phosphorus, sodium, and zinc in fortified
food products.)
Upper limits (mg/kg): Ca (24000); Cu (210); Fe (850);
K (32000);Mg (7500);Mn (20);Na (16000); P (16000);Zn (320).
Limit of quantitation (LOQ; mg/kg): Ca (150); Cu (2); Fe (10);
K (200);Mg (50);Mn (0.05);Na (100); P (100); Zn (5).
See
Tables
2011.14A
–
I
for the results of the interlaboratory
study supporting acceptance of the method. [
Note
: Results shown
in Tables
2011.14A
–
I
are slightly different from those shown in
J. AOAC Int
.
92
, 1484(2009) due to classical statistics applied
insteadof robust statisticsapplied in the tables included in
J.AOAC
Int
.
95
, 177(2012).]
Digestion
A. Principle
Test portion isheated at 200°C eitherwithnitric acid in a closed-
vessel microwave digestion system (MDC) or with a combination
ofhydrogenperoxide, nitricacid, andhydrochloricacid inanopen-
vesselmicrowave digestion system (MDO).
B. Apparatus
Microwave
.
____
Commercial MDC or MDO designed for
laboratory use at 200 ± 20°C, up to 600 psi, and controlled
temperature or pressure ramping capability. It is recommended
that vessel design be selected
that will withstand the maximum
possible pressure (600 psi) since organic residues of rich-fat or
rich-carbohydrate samples, if not given sufficient time topredigest,
will generate significant pressure during digestion.
C. Reagents
(
a
)
High-grade water, (18 MΩ)
.—For slurry preparation and/
or dilution.
(
b
)
Nitric acid (HNO
3
), 65% (w/v)
.—Trace metal grade
throughout.
(
c
)
Hydrochloric acid (HCl), 37% (w/v)
.—Trace metal grade
throughout.
(
d
)
Hydrogen peroxide (H
2
O
2
), 97% (w/v)
.—Tracemetal grade
throughout.
D. Determination
[
Caution
: Before using chemicals, refer to the supplier guide
for chemical safety and/or other adequate manuals or safety data
sheets approved by local authorities. Use fume hood andwear full
personal laboratory protective clothing, gloves, and appropriate
eyeprotection (safetyglasses)whenusingglassware andpreparing
standards or test portionswith acid solutions.]
(
a
)
Sample preparation
.—(
1
)
Test sample preparation
.—
Homogenize a representative sample by grinding as finely as
possible and/or by preparing a slurry with H
2
O.
For example
:
Infant cereals and fortified milk powders, preheat water at 50°C.
Prepare the slurry byweighing 10.0 ± 0.1 g test sample and place
into a 100mL
Erlenmeyer flask; add 90.0 ± 0.1 g H
2
O. Mix well
with stopper.
(
2
)
Test portion preparation
.—Accurately weigh 0.50 ± 0.01 g
test portion or sample mass on a dry weight basis in the prepared
slurry toMDCvessel (1.00±0.01g intoa100mLvolumetricflask
forMDO). [
Note
:An optimal analytical test portionmass of 0.5 g
(1.0g forMDO) is basedon an empiricalmaximum energy release
by the food of 3 kcal and 90–110% recovery.]
Line theMDC vessel walls or Pasteur pipet withweighing paper
during sample transfer to keep sample from adhering to sides of
vessel or use aPasteur pipet to transfer liquid samples. (Weighfluid
samplesor test portion from slurry test sampledirectlyaftermixing.)
(
Note
: Removeweighing paper from sample prior to next step.)
Carefully add 5.0 ± 0.1mLHNO
3
intoMDC/MDO vessel (and
then 5mLH
2
O
2
only intoMDO vessel).
Loosely capMDC vesselwithout sealing.
Table 2011.14A. Interlaboratory study results for calcium
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
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 NISTSRM2387 409.90
(411)
h
100 13.37
3.26
28.20
6.88
1.06
9
NS
Wheat glutenNISTRM 8418
367.56
(369)
h
100
3.51
0.95
12.90
3.51
0.53
7
2, 4C
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
FORWORKINGGROUP/ERPUSEONLY
DONOTDISTRIBUTE
