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P
oitevin
:
J
ournal of
AOAC I
nternational
V
ol
.
95, N
o
. 1, 2012
183
using only one internal standard line. Following is the list of
wavelengths for each element (and its appropriate internal
standard), in priority order, that have been found acceptable for
main foodstuffs: Wavelength (nm): Ca: 317.933 (In: 303.936);
Cu: 324.754 (In: 303.936); Fe: 259.94 (Sr: 338.071); K: 766.491
(Sr: 460.733); Mg: 285.213 (In: 303.936); Mn: 257.610 (Sr:
338.071); Na: 589.592 (Sr: 460.733); P: 213.618 (In: 303.936);
and Zn: 213.857 (Sr: 338.071).
Other wavelengths that are acceptable for both elements and
internal standards could be used as confirmatory analytical lines
or alternate wavelengths as certain recommended lines may not
be available on some ICP-OES systems: Wavelength (nm): Ca:
317.933 (Y: 371.028); Cu: 324.754 (Y: 371.028), 327.395 (In:
303.936 or Y: 371.028); Fe: 259.94 (Y: 371.028 or Cr: 283.563);
Mg: 285.213 (Y: 371.028), 279.028 (In: 303.936); Mn: 257.610
(Sr: 460.733 or Y: 371.028); P: 178.222 (Sr: 460.733 or Y:
371.028); and Zn: 213.857 (Sr: 460.733 or Y: 371.028).
Other lines of appropriate sensitivity, free of interferences or
corrected for interferences in specific matrixes, may be just as
acceptable.
G. Reagents
(
a
)
Ionization buffer/internal standard solution
.—Weigh
1.27 g cesium chloride into a 1000 mL acid-washed volumetric
flask.
Note
: This cesium 0.1% (w/v) solution was tested as the
minimal recommended concentration required for element
analysis in most food matrixes. Cs solution 1% (w/v) is
recommended if an element is present at low concentration
in high-salted food raw materials, e.g., culinary products or
tastemakers, or if it is analyzed as an impurity in food-grade salts.
Add 40 mL indium 1000 mg/kg and 10 mL each of strontium,
yttrium, and chromium 1000 mg/kg stock standard solutions as
internal standards. Add 10 mL HNO
3
. Dilute to volume with
H
2
O, mix, and transfer to an acid-washed polyethylene bottle.
Note
: Reagent concentrations assume the use of same pump
tubing internal diameter for both internal standard/ionization
buffer and sample pump tubes using automatic addition.
(
b
)
Stock standard solution
.—Working standards can be
prepared from ICP-grade individual element 1000 mg/kg
(e.g., for copper, iron, manganese and zinc) and 10 000 mg/kg
Table 2011.14J. Suggested concentration of the six standard solutions, mg/kg
Element
Std0
Std1
Std2
Std3
Std4
Std5
Std6
Ca
0
7.5
15
30
75
150
225
Cu
0
0.05
0.1
0.2
0.5
1.0
1.5
Fe
0
0.25
0.5
1.0
2.5
5
7.5
K
0
10
20
40
100
200
300
Mg
0
2.5
5
10
25
50
75
Mn
0
0.00125
0.0025
0.005
0.0125
0.025
0.0375
Na
0
5
10
20
50
100
150
P
0
5
10
20
50
100
150
Zn
0
0.1
0.2
0.4
1.0
2.0
3.0
Table 2011.14I. Interlaboratory study results for zinc
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
18.06
NA
g
0.396 2.19
0.95
5.24
0.51
8
5–SG
Dietetic milk powder 2
53.65
105 1.43 2.66
2.36
4.40
0.50
9
NS
h
Infant cereal
36.51
NA 0.92 2.25
1.27
3.44
0.37
9
NS
Peanut butter
NIST SRM 2387
26.64 (26.3)
i
101 1.06 3.96
1.78
6.69
0.69
9
NS
Wheat gluten
NIST RM 8418
49.30 (53.8)
i
92
0.96
1.95
3.19
6.46
0.73
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
SG = Single Grubbs outlier.
g
NA = Not available.
h
NS = Not significant.
i
Certified or reference values.
2011.14 (MTE-01) MLT
FOR ERP USE ONLY
DO NOT DISTRIBUTE