Analytical methods for the determination of various forms of fluoride in toothpastes

Fluoride (F) toothpastes, properly formulated and tested to show chemical activity, stability and clinical efficacy, are the most important components of caries prevention programmes. Analytical methods, based on the use of a F- -specific electrode, for the determination of various F species (ionic, soluble and total F) in toothpastes were investigated. The methods involved analysis of F species in the supernatants, suspensions and precipitates (residues) of 20 per cent aqueous slurry of toothpastes as well as in the pastes themselves. The ionic F (F-) concentration was determined by the addition of acetate buffer (7.5 M, pH 5.2; containing a metal-chelating agent) to the supernatant of slurried toothpastes. The soluble F (F- plus F of hydrolysed PO3F2-) in the supernatants was determined by direct acid hydrolysis in 0.8 M HCl, at room temperature (23 + 1 degree C), for 3, 12 or 24 h and in 2.3 M HCl, at 50 degrees, for 10, 20 or 40 min. The total F concentration in the suspensions (slurries) and in the pastes was determined using acid-hexamethyldisiloxane (HMDS) diffusion; a method which hydrolysed PO3F2- and separated F as well. Inaccuracy was encountered in the determination of ionic and soluble F in the suspensions of slurried toothpastes. There was a good agreement (r = 0.997) between the soluble and total F concentrations in the supernatants of monofluorophosphate (Na2PO3F; MFP) toothpastes, suggesting that the two methods, i.e. direct acid hydrolysis and acid-HMDS diffusion, can interchangeably be used.(ABSTRACT TRUNCATED AT 250 WORDS)