Fluoride Determination in Milk, Soy, and Water-Based Products Using Ion-Selective Electrode and Direct Measurement Technique: Single-Laboratory Validation, First Action 2022.05.

This article focuses on the validation of a fluoride ion-selective electrode (F-ISE) method for determining fluoride concentrations in infant formula and adult nutritional products, as specified by the AOAC Stakeholder Panel on Infant Formula and Adult Nutritionals (SPIFAN) Standard Method Performance Requirement (SMPR) 2014.016. The method involves reconstituting powdered samples, adding hydrochloric acid to release bound fluoride, and using sodium citrate buffer to adjust pH and complex interfering ions before analysis with F-ISE. Validation results demonstrated that the method meets SMPR criteria for limit of quantitation, precision, accuracy (94–98% recovery), and ruggedness across various formula matrices, leading to its adoption as an AOAC First Action Official Method. The F-ISE method is noted for its affordability, ease of use, and specificity, with minimal interference when samples are maintained at pH above 5.0.