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Method Performance
Part 1 of the method evaluation within participating laboratories involved the
calibration parameters the LOQ and a practice sample. The NIST 1849a CRM was
selected for this purpose because it was readily available in most laboratories,
since the expected values are known, participant could get instant feedback on
the method was working appropriate. It provides additional confidence that no
bias in the operation of the method amongst all participants. Two participating
laboratories showed bias for the NIST 1849a and were not qualified. All other 12
laboratories provided acceptable data for the practice sample. All collaborators
returned acceptable calibration parameters based on linear regression
correlation coefficients or quadratic regression (r
2
0.9942-1.0000).
Laboratory 2 was not capable to measure P. Laboratories having problems with
Fe, Cu, Mn, at low range in placebos and dairy products were excluded from
statistical treatment (negative values). All remaining data were statistically
analyses using the AOAC protocol for overall mean, intra-laboratory repeatability
(Sr), repeatability relative standard deviation (RSDr), inter-laboratory
reproducibility (SR), reproducibility relative standard deviation (RSDR) and
HorRat. Cochran (p=0.025, 1 tail) and Grubbs (single and double), p=0.025, 2-
tail) tests were utilized to determine outliers. In some instances statistical
outliers were identified but deemed reasonable to do so, these were retained in
the data set for calculation of precision of method.
Results of the laboratories showed no bias with the certified values from NIST
(also measured with ICP-AES)
Table 2: Interlaboratory study results for NIST 1849a with certified values obtained by
ICP-AES.
Summary of the summary tables is shown in the next three tables for infant
formula and adult nutrition product, for the Placebo samples and for the dairy
samples.
Element
Mean (mg/kg)
Calcium (Ca)
5302
5253 ± 51
Copper (Cu)
19.47
19.78 ± 0.26
Iron (Fe)
174.0
175.6 ± 2.9
Magnesium (Mg)
1634
1648 ± 36
Manganese (Mn)
48.87
49.59 ± 0.97
Phosphorus (P)
4009
3990 ± 140
Potassium (K)
9319
9220 ± 110
Sodium (Na)
4269
4265 ± 83
Zinc (Zn)
152.6
151
± 5.6
Certified value (mg/kg)
2011.14 (APRIL 2017) - MTE-01/03
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