Analysis of Fluoride Concentration in Dentifrice Containing Potassium Nitrate and Sodium Bicarbonate

Potassium nitrate and sodium bicarbonate are added to some dentifrices, and these ingredients interfere with the accurate measurement of fluoride release rate by ion selective electrode (ISE) as described in the ADA Guidelines for Fluoride-Containing Dentifrices, “Measuring the Fluoride Release Rate of Dentifrices”. Objective: This study demonstrates that the addition of potassium nitrate as a desensitizer and/or sodium bicarbonate as abrasive/flavor enhancer in dentifrice formulations interferes with current methods of ISE fluoride release rate analysis. Methods: Different formulations of sodium fluoride dentifrice examples were selected to include a) potassium nitrate, b) sodium bicarbonate, c) both and d) neither. Solutions of three parts water to one part sample for each dentifrice were prepared, and fluoride ion concentration was measured using ISE. Ion chromatography (IC) fluoride concentration measurement was used as the standard for comparison. Results: Both IC and ISE provided accurate fluoride ion release rate determination when neither potassium nitrate nor sodium bicarbonate was included in the formulation. Large error values for fluoride ion release rate concentrations, however, were detected in ISE analyses of dentifrice that included potassium nitrate (7.0 – 14.2% over estimate), sodium bicarbonate (18.6% over estimate) or both (27.3% over estimate). Conclusion: The ISE method is an easy, fast, and low cost method for fluoride release rate measurement, and is adequate for measurement of fluoride release rate in dentifrices containing no potassium nitrate or sodium bicarbonate. To achieve correct values in fluoride release rate analyses of dentifrice with potassium nitrate or sodium bicarbonate, IC or a modified ISE method should be used.