182
P
oitevin
: J
ournalof
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 tomaximizemixing accuracywhile
maintaining the required detection levels.
Ionization buffer (cesium chloride) is combined with the
internal standardsolution tocompensateEIEeffects (e.g.,K,Na,
andCa) in the plasma, since certain foodmaterials 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 5000mg/kg cesium for high-salted food rawmaterials (e.g.,
culinaryproducts or tastemakers) and aminimumof 500mg/kg
cesium (formain food samples), 20mg/kg indium and5mg/kg
strontium,yttrium, andchromium, less thanhalfofeachelement
concentrationof thehigherworking standardStd6, and less than
0.5 g/kg total dissolvedminerals.
Power settings and nebulizer gas flowmust be optimized to
ensure that theMg280.271: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
bedetermined and internal standards.As aminimum, select one
recommended and one alternativewavelength 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
Chocolatemilk powder
1927.84
97 43.30
2.25
51.07
2.65
0.52
9
NS
g
Dieteticmilk 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
NISTSRM 2387
4924.12 (4890)
h
101 158.61 3.22
158.61
3.22
0.72
9
NS
Wheat gluten
NISTRM 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 laboratoriesminus outliers.
f
SG=SingleGrubbs outlier.
g
NS=Not significant.
h
Certifiedor 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
Chocolatemilk powder
4138.12
101 84.53 2.04 115.22 2.78
0.61
9
NS
f
Dieteticmilk 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
NISTSRM 2387
3444.06 (3378)
g
102 98.10 2.85 111.97 3.25
0.69
9
NS
Wheat gluten
NISTRM 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 laboratoriesminus outliers.
f
NS=Not significant.
g
Certifiedor reference values.
MTE-01
FORWORKINGGROUP/ERPUSEONLY
DONOTDISTRIBUTE
