STABILITY OF MONOFLUOROPHOSPHATE AND FLUORIDE IONS IN DENTIFRICE 9 7 4O 2O t_ o ß ß O I I I I I I I I I00 200 300 4O0 Doys Figure 4. Changes of free fluoride ions in test dentifrices A (0) and B (0) during storage. 40- T 20- • • o • O ß I00 200 300 400 Days Figure 5. Changes of free fluoride (¸) and monofluorophosphate (ß) ions in test dentifrice C during storage. T E •L Figure 6. 40- I I I I I I I I00 200 500 400 Doys Cl•s ooe oeree fluoride (0) and raonofluorop•osp•ate (•) ions test dentifrice D during storage.

l0 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS T • 20 o o • 0 0 u 0 0 O-- o I I I I' I [ I I IOO 200 500 doo Doys Figure 7. Changes of free fluoride (¸) and monofluorophosphato (0) ions in test dentifrico E during storage. 40- ß '8 20- _ /• o•ø o c • 9 • n o-. I00 200 300 400 Days Figure 8. Changes o[•r• a•oriae (0) a•a mo•oa•oropbospbate (•) ions i• test dentifrice P d•ri• storage. (II) is reached and then starts to increase (see C and D, Figs. 5 and 6). In toothpaste E, with an initial ratio monofluorophosphate: fluoride of 2: 4, the fluoride content was constant during the first year (Fig. 7). According to reaction (I) the monofluorophosphate content decreases in all test toothpastes where it is present (Figs. 5-8). The results clearly demonstrate that it is possible to add sodium fluoride to a dentifrice containing calcium carbonate without getting a total in- activation of the free fluoride ions. As the rate and equilibrium constants of reactions (I) and (II) are dependent on the environmental conditions no assumptions can be done about the fluoride ions behaviour in dentifrices with different basic formulas.