AOAC SPIFAN Nutrients ERP (December 7, 2022)

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

5 Results

5.1 Linearity Linearity was determined on nine days by analyzing each calibration sample in single. An unweighted linear least squares regression, not forced through zero, was used as calibration curve. Typically in our laboratory most analyzed infant formula samples result in values in the lower range of the calibration curve (0–1.0 µg fluoride/vial). In this validation study, samples containing fluoride up to amounts of 12 µg/vial were also included. Therefore the calibration range was extended to 10 and 20 µg/vial on several days. All data of the calibration curves is shown in Table 4, including the coefficient of determination R 2 . Typical calibration plots are shown in Figure 3. When fluoride levels were below 1 µg/vial, the 0–1.0 µg calibration was used to quantify the amount. In case of higher amounts the appropriate calibration was used.

Table 4. Data of the calibration curves determined on different occasions. Function R 2 Range (µg/vial) Instrument

Day

Technician

y = 203x + 0.233 y = 206x - 0.0110 y = 332x + 2.31 y = 325x + 3.80 y = 322x + 7.48 y = 330x + 3.46 y = 318x + 4.76 y = 282x + 3.33 y = 210x + 7.74 y = 220x + 0.112 y = 225x - 0.139 y = 341x - 1.97 y = 225x - 0.902 y = 351x - 4.34 y = 341x - 9.86 y = 307x - 10.7 y = 214x - 0.800

0.999932 0.999947 0.999491 0.999977 0.999952 0.999927 0.999918 0.998982 0.999990 0.999918 0.999913 0.999865 0.999998 0.999955 0.999936 0.999828 0.999999

0–1.0 0–1.0 0–1.0 0–1.0 0–1.0 0–1.0 0–1.0 0–1.0 0–1.0 0–1.0 0–1.0

A A B B B B B B A A A B A B B B A

1 2 1 2 3 4 5 6 7 8 9 3 9 4 5 6 7

A A B A A A A A A A A A A A A A A

0–10.0 0–10.0 0–20.0 0–20.0 0–20.0 0–20.0

Figure 3. Calibration curves in the range of 0–1.0 (left) and 0–20.0 µg (right) fluoride per vial.