AOAC SPIFAN Nutrients ERP (December 7, 2022)

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

Calibration samples are prepared according to Table 2. Note that absolute amounts of fluoride are used as working unit. In our laboratory values for F⁻ are typically reported as mg/kg dry powder. In SPIFAN documentation the unit µg/100 g reconstituted final product is often used. Since 0.3 g of material is weighed into a vial, the units can be converted as follows: 0.5 µg fluoride in 0.3 g of sample corresponds to 1.67 mg/kg powder. With a 9-fold (25 g into 200 g water) dilution, as described in the SMPR (Figure 2), this corresponds to 18.5 µg/100 g reconstituted final product. These converted units are shown in the right columns of Table 2.

Table 2 . Preparation of calibration samples and range expressed in different units. Final amount 10 mg/L std. 1 mg/L std. water Equiv. dry powder

Equiv. reconst.

(µg F⁻ absolute/vial)

(µL)

(µL)

(mL) 2.00 1.95 1.90 1.80 1.95 1.90 1.75 1.00 0.50 0.00

(mg/kg)

(µg/100 g)

0.00 0.05 0.10 0.20 0.50 1.00 2.50 10.0 15.0 20.0

0

0.000 0.167 0.333 0.667 1.67 3.33 8.33 33.3 50.0 66.7

0

50

1.85 3.70 7.41 18.5 37.0 92.6 370 556 741

100 200

50

100 250

1000 1500 20000

4.5 Calculations Calculate the absolute amount of fluoride in µg/vial in the test sample from the calibration curve (using unweighted linear regression, not forced through zero). The concentration of fluoride (test sample) is calculated as followed:

fluoride, mg/kg = C/W

Where C is the amount of fluoride in the vial from the calibration curve (µg) and W is the weight of the test portion (g).

4.6 Preparation of test sample Weigh in an aliquot of 0.3 g of infant formula into a 20-mL headspace vial and suspend it in 2 mL 3.0 M sulfuric acid. Add 10 µL of TMCS to derivatize fluoride to TMFS. In case of inhomogeneous samples, a sample solution can be prepared by dissolving 25 g of sample in 200 mL water, and then 2 mL transferred to a 20-mL headspace. Then 2 mL 3.0 M sulfuric acid is added and mixed, then followed by the addition of 10 µL TMCS. This method is similar if one requires the concentration in reconstituted infant formula. In this report an example of a slurry analysis is included as well.