AOAC SPIFAN Nutrients ERP Method Reviews (September 7, 2019)

Besides the temperature and the pH that could affect the results, cations, especially calcium and magnesium, could form insoluble salts with fluoride. Their solubility products (Ksp) are very low. The existence of these cations could reduce the free fluoride ion levels in sample and affect the results. 7. Any general comments about the method? * It seems that the temperature can affect the measurement results. It would be useful to investigate the effect of temperature variation in the ruggednesses testing. The recovery data from spiking experiments looks good, but it would be complete to have another approach to verify the accuracy of the method. This method measures the free form of fluoride, not the bounded form of fluoride. The SMPR does not specifically say the total fluoride, but it is believed that the total fluoride is required to be measured. Recommendation for the Method V. Final Recommendation Do you recommend this method be adopted as a First Action and published in the Official Methods of Analysis of AOAC INTERNATIONAL? Please specify rationale. * I am not ready to recommend this method be adopted as a First Action method because: 1) The Accuracy of this method need to be checked by a second approach in addition to the spiking approach. 2) The potential interference from cations (Ca2+, Mg2+, Al3+, etc.) need to be investigated. Insoluble salts could be formed and lead to reduced fluoride concentration. 3) Additional data on the LOD/LOQ assessment is needed.