AOAC SPIFAN Nutrients ERP (December 7, 2022)

Fluor-06 (SLV) 10-2022 FOR ERP USE ONLY DO NOT DISTRIBUTE

5.2 Limit of quantification (LOQ) Optimally the LOQ is determined in a blank sample matrix. Since no absolute blank infant formula is available, the LOQ was determined from the recovery of spiked samples with a low native concentration of fluoride. The required recovery at the LOQ level is 80–120%. The values found are shown in Table 5. Since recoveries found were in the range of 90–102% the LOQ is established at 0.05 µg fluoride per vial which translates to 0.167 mg/kg dry powder and 1.85 µg/100 g reconstituted final product.

Table 5. Recoveries determined at LOQ level.

Day 1

Native (µg/vial) Total (µg/vial) Spiked (µg/vial) Recovery (%) Native (µg/vial) Total (µg/vial) Spiked (µg/vial) Recovery (%)

0.0928 0.1425

0.0823 0.1323

0.0872 0.1384

0.0878

0.09

0.0815 0.1299

0.139

0.1383

0.05 100

0.05 100

0.05 102

0.05 102

0.05 97.0

0.05 96.7

Day 7

0.0831

0.0813 0.1281

0.0759 0.1223

0.0792 0.1268

0.0815 0.1299

0.0765

0.128

0.125

0.05 89.9

0.05 93.5

0.05 92.9

0.05 95.2

0.05 96.7

0.05 97.0

5.3 Specificity and selectivity Analyte specific retention times of compounds separated by chromatography substantiate the selectivity. The requirement for specificity was that the retention time of TMFS in samples should not deviate more than 2.5% from retention times in an analytical standard. The results are shown in Table 6 and in all cases are within the required limit. Table 6. Retention times of TMFS in various samples and a standard. Sample Retention time (min) Deviation (%) from standard SRM1869 9.618 0.04 RM8260 9.620 0.06 RM8261 9.618 0.04 SRM1849a (NIST IF A3) 9.619 0.05 NIST10175 (IF C-1) 9.621 0.07 1.0 µg F 9.614 -

Besides the retention time, the chromatograms are inspected visually as well. The peak shape of TMFS in infant formula samples should be similar to that in a standard sample (see Figure 4).