Fluor determination in toothpaste-extracts with fluoride-selectrode based on the kinetics of hydrolysis of sodiummonofluorophosphate.
The Sodiummonofluorophosphate is used in a large number of toothpastes, s, while clinical research proved that application of fluoride has an important contribution in caries prevention. This prevention is almost due to the reconstitution of the by acids disappeared hydroxylapatite Ca10 (PO4)6 (OH)2 in the toothsurface, which process goes two to three times faster in the presence of F- by sedimentation of hydroxyfluorapatite Ca10 (PO4)6 (OH)2-xFx, with a higher chemical resistance for acids. Therefore, the F- must been released from the FPO3-- during the application of the pasta, e.g. by hydrolysis in the mouth. Solutions of Na2FPO3 seem to release an important amount of free F- ions, without addition of acid, and as a function of concentration, time and temperature. The hydrolysis of FPO3-- is pH-dependent and can be studied as a pseudo-first-order reaction. The dependence of the pH is found in the kinetic expression: -dC/dt = k. [H2PO3F] [H+] = k1.C, where C is the total formal concentration of all monofluorophosphate species at time t. The Arrhenius energy of activation is 16.42 +/- 0.1 Kcal/mole. The hydrolysis of monofluorophosphoric acid has already been studied before. In the present work additional F(-)-determinations are performed with a specific F(-)-selectrode, without any interference of the monofluorophosphate species, which was warned for by other authors. More recent investigation showed that in samples of controlled ionic strength little interference occurs, and phosphates in particular do not interfere. Fresh prepared solutions of Na2FPO3 were used at different pH and different temperature.(ABSTRACT TRUNCATED AT 250 WORDS)
Heidbüchel
P W
PW
Chemical Engineering Department, Katholieke Universiteit Leuven, Belgium.
D004566:Electrodes; D005459:Fluorides / Q000032:analysis* / Q000737:chemistry*; D006868:Hydrolysis; D007700:Kinetics; D010710:Phosphates / Q000737:chemistry*; D014100:Toothpastes / Q000032:analysis*
D010710:Phosphates; D014100:Toothpastes; C012980:fluorophosphate; D005459:Fluorides