138 / 620
checked daily throughout the batch run. The system was recalibrated when the percent error of
the check standards was > 5%.
Error, % = calculated concentration – actual concentration actual concentration × 100
Accuracy
Accuracy was determined by fortifying the placebo samples (prior to sample preparation)
at 50 and 100 % of the typical level of fluoride found in a powdered infant formula. These
recovery experiments were performed over multiple days on two different instruments. In
addition, NIST SRM 1849a was analyzed during the course of this validation. Table 2 contains
recovery results for fluoride on the five placebo samples respectively.
The percent fluoride recovered ranged from a low of 73.8% to a high of 166%. The
percent relative standard deviations (RSD) ranged from a low of 2.45% to a high of 15.3%. The
overall mean recovery is 96.7% with a RSD of 31.4%. With the exception of three recovery
value at 73.8%, 77.1% and 166%, all data meets the criteria specified in the SMPR (80-120%
recovery).
Results on NIST SRM 1849a can be found in Table 3 &4. The mean value of fluoride
was found to be 208 µg/100g (n = 30) with % RSD 5.94. The certified value and range for
fluoride are not provided in the SMPR.
Precision
Repeatability was evaluated on all 12 fortified AOAC SLV test material matrices
including the NIST SRM 1849a using multiple instruments. Samples and standards were
prepared freshly every day over six days and analyzed in triplicate to calculate the intermediate
and overall reproducibility. Precision data for all samples can be found in Tables 5.
Fluoride concentration ranged from 52.6 to 231 µg/100 g. Overall precision was < 19%
for all samples. Percent relative standard deviations ranged from a low of 2.57% to a high of 18.5
%.
Reproducibility
Reproducibility was determined in the precision experiments conducted over multiple
days and involving different lots of reagents made fresh each analysis day. In addition, two
instruments were used during this validation study.
Limit of Detection (LOD) and Limit of Quantitation (LOQ)
The LOD was estimated as 3× the signal-to-noise ratio (S/N) and the LOQ as 10× the
S/N. The system baseline noise for the LOD and LOQ was determined by measuring peak-to-
Fluor-02 SLV
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