What could be the cause of a white precipitate formation during chlorhexidine mouthwash with zinc chloride and sodium fluoride production.we are using citric acid sodium citrate as buffer sodium saccharine at 0.04% glycerine 3%,tween 60, peppermint oil dm water but after 4 days storage it forms white stubborn deposit.
Probabely the reason could be hydrolysis reaction of Zinc chloride to form white precipitate of Zinc hydroxide - Zn(OH)2
Zn2+ + 2OH- -> Zn(OH)2(s)
When hydrated zinc chloride is heated, one obtains a residue of Zn(OH)Cl e.g.
ZnCl2·2H2O → ZnCl(OH) + HCl + H2O
It may also form Zinc fluoride -ZnF2 from the reaction of Zinc chloride and Sodium fluoride,
ZnCl2 + 2NaF = ZnF2 + 2NaCl
Zinc fluoride is practically insoluble in water and may form white precipitate.
As all above reactions are pH dependent, please adjust pH of mouth wash product appropriately to avoid precipitation.
However, please carry out compatibility studies of all ingredients used in the mouthwash formulation. Suggested to perform this by eliminating one ingredient in each experiment to find out exactly which ingredient is responsible to form white precipitate. You should have performed the compatibility studies at the time of product development in R & D.
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Thank you sir.about compatibility studies,the formulations available and desired by our clients is with the above APIs zncl,NaF and chlorhexidine
.1.what would you advice as best ph?we are at a ph of 6.
2.does sodium sachaarine conc affect the stability in your opinion.
I can understand that this formulation is acording to clients requirements. Therefore, you will not be able to change the API ingredients. However, you may modify other excipients and pH of the product.
You may also study existing similar marketed products.
Before adjusting pH of the product please perform compatibility studies. This will identify which ingredient is responsbile for precipitation. Accordingly we you can decide further course of actions.
Thanks alot, appreciated.be blessed.
You are always welcome.