Development of gold standard ion-selective electrode-based methods for fluoride analysis.

BACKGROUND/AIMS: Currently available techniques for fluoride analysis are not standardized. Therefore, this study was designed to develop standardized methods for analyzing fluoride in biological and nonbiological samples used for dental research. METHODS: A group of nine laboratories analyzed a set of standardized samples for fluoride concentration using their own methods. The group then reviewed existing analytical techniques for fluoride analysis, identified inconsistencies in the use of these techniques and conducted testing to resolve differences. Based on the results of the testing undertaken to define the best approaches for the analysis, the group developed recommendations for direct and microdiffusion methods using the fluoride ion-selective electrode. RESULTS: Initial results demonstrated that there was no consensus regarding the choice of analytical techniques for different types of samples. Although for several types of samples, the results of the fluoride analyses were similar among some laboratories, greater differences were observed for saliva, food and beverage samples. In spite of these initial differences, precise and true values of fluoride concentration, as well as smaller differences between laboratories, were obtained once the standardized methodologies were used. Intraclass correlation coefficients ranged from 0.90 to 0.93, for the analysis of a certified reference material, using the standardized methodologies. CONCLUSION: The results of this study demonstrate that the development and use of standardized protocols for F analysis significantly decreased differences among laboratories and resulted in more precise and true values.

Evaluation of the direct and diffusion methods for the determination of fluoride content in table salt.

OBJECTIVE: The aim of this study was to assess methods currently used for analyzing fluoridated salt in order to identify the most useful method for this type of analysis. BASIC RESEARCH DESIGN: Seventy-five fluoridated salt samples were obtained. Samples were analyzed for fluoride content, with and without pretreatment, using direct and diffusion methods. Element analysis was also conducted in selected samples. Fluoride was added to ultra pure NaCl and non-fluoridated commercial salt samples and Ca and Mg were added to fluoride samples in order to assess fluoride recoveries using modifications to the methods. RESULTS: Larger amounts of fluoride were found and recovered using diffusion than direct methods (96%-100% for diffusion vs. 67%-90% for direct). Statistically significant differences were obtained between direct and diffusion methods using different ion strength adjusters. Pretreatment methods reduced the amount of recovered fluoride. Determination of fluoride content was influenced both by the presence of NaCl and other ions in the salt. CONCLUSION: Direct and diffusion techniques for analysis of fluoridated salt are suitable methods for fluoride analysis. The choice of method should depend on the purpose of the analysis.