Simultaneous determination of free fluoride and monofluorophosphate in toothpaste by capillary electrophoresis with capacitively coupled contactless conductivity detection

Capillary electrophoresis (CE) with capacitively coupled contactless conductivity detection (C4D) was used for rapid, accurate and simultaneous determination of free fluoride and monofluorophosphate (MFP) in six different toothpaste samples. A buffer solution containing 15 mmol L−1 histine, 25 mmol L−1 lactic acid, and 2.5 mmol L−1 tetradecyltrimethylammonium bromide (TTAB) was used as background electrolyte (BGE). A complete separation of the analytes and the internal standard (tartrate) could be attained in less than 2.5 min. The limits of detection (LOD) and quantification (LOQ) were, respectively, 0.17 and 0.57 mg L−1 for free fluoride and 0.70 and 2.33 mg L−1 for MFP. Recoveries ranging from 85 to 107% were obtained for samples spiked with standard solutions of free fluoride or MFP. The CE-C4D method was compared to an ion-selective electrode (ISE) method and the results were in good agreement. More importantly, the CE-C4D method demonstrates the advantage of being able to determine MFP without a prior hydrolysis step.