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oitevin
:
J
ournal of
AOAC I
nternational
V
ol
. 95, N
o
. 1, 2012
precision. Follow manufacturer’s recommendations. Select
peristaltic pump rotation speed, sample, and internal standard
pump tubes of similar size to maximize mixing accuracy while
maintaining the required detection levels.
Ionization buffer (cesium chloride) is combined with the
internal standard solution to compensate EIE effects (e.g., K, Na,
and Ca) in the plasma, since certain food materials can contain
substantial concentrations of these elements. This provides a
significant source of electrons in the plasma. The presence of
ionization buffer in all samples and standards will minimize
the effects of varying concentrations of EIEs in the sample.
The solution presented to the nebulizer contains a maximum
of 5000 mg/kg cesium for high-salted food raw materials (e.g.,
culinary products or tastemakers) and a minimum of 500 mg/kg
cesium (for main food samples), 20 mg/kg indium and 5 mg/kg
strontium, yttrium, and chromium, less than half of each element
concentration of the higher working standard Std6, and less than
0.5 g/kg total dissolved minerals.
Power settings and nebulizer gas flow must be optimized to
ensure that the Mg280.271:Mg285.213 ratio (Mermet principle
of robust plasma) demonstrates robust operating conditions
in accordance with the ratio established by the instrument
manufacturer. At least three replicate readings of the same
sample are performed, with relatively long integration times to
minimize noise.
(
b
)
ICP wavelengths
.—A number of recommended and
alternative wavelengths may be used for the nine elements to
be determined and internal standards. As a minimum, select one
recommended and one alternative wavelength for each element
corrected by one recommended wavelength for appropriate
internal standard. All responses for both recommended
and alternative wavelengths for each element are corrected
Table 2011.14G. Interlaboratory study results for sodium
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
1927.84
97 43.30
2.25
51.07
2.65
0.52
9
NS
g
Dietetic milk powder 2 1769.19
96 18.64
1.05
33.39
1.89
0.36
9
NS
Infant cereal
992.41
95 37.67
3.80
39.72
4.00
0.71
8
6–SG
Peanut butter
NIST SRM 2387
4924.12 (4890)
h
101 158.61 3.22
158.61
3.22
0.72
9
NS
Wheat gluten
NIST RM 8418
1346.82 (1420)
h
95
19.56
1.45
26.85
1.99
0.37
8
6–SG
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
NS = Not significant.
h
Certified or reference values.
Table 2011.14H. Interlaboratory study results for phosphorus
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
Chocolate milk powder
4138.12
101 84.53 2.04 115.22 2.78
0.61
9
NS
f
Dietetic milk powder 2 3729.50
100 46.37 1.24 101.72 2.73
0.59
9
NS
Infant cereal
4341.81
101 60.56 1.39 111.79 2.57
0.57
9
NS
Peanut butter
NIST SRM 2387
3444.06 (3378)
g
102 98.10 2.85 111.97 3.25
0.69
9
NS
Wheat gluten
NIST RM 8418
2050.02 (2190)
g
94
37.86
1.85
67.15
3.28
0.65
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
NS = Not significant.
g
Certified or reference values.
2011.14 (MTE-01) MLT
FOR ERP USE ONLY
DO NOT DISTRIBUTE