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Question

Posted on: April 8 2014

Crystals in modified sugar-free cough syrup with dextromethorphan from TMF

We make the syrup according to the guidelines of the TMF, but replace the banana aroma by eucalyptol (concentration 0.2 g/l), we also add a green dye (viride 7069, 100 mg/l). First, Dextromerofan is mixed with sorbitol, then the citric acid is added. In a separate cup with water, the amount after saccharin is dissolved and poured into the previous mixture. Then Eucalyptol is added and filled with water for preservation up to approximately final volume. Finally, the potassium sorbate is dissolved in a separate cup with some water for storage and attached to the whole. The dye is finally brought to the solution. During all the different steps of the process, the various substances are dissolved. In the end, with the addition of potassium sorbate, after a while very fine crystals are formed. We think that the solubility of potassium sorbate enters into competition with that of Dextrometorfan. The pH of the solution is 4 to 5. So we ask ourselves how we can avoid these crystals.

Answer

I have not yet heard of precipitation in the Dextrometorfansyrup TMF. So I find the problem in the dyes, which you add first to Dextrometorfansyrup TMF

Tartrazine is an after salt and consequently, the dye is an anion;   Patent Blue V is an acid and reacts with citric acid with after saccharinate, K sorbate and Na-tartrazine.  

Tartrazine:

Patent Blue:

You indicate that the pH of the Final Solution is 4 to 5. So I suppose there are still   different anions in the solution, which may react with dextrometorfanH +. On the composition of dextrometorfanhydrobromide syrup TMF, I have to point the finger at tartrazine. If we lower the pH even with citric acid (250 mg?)   to 3 to 4 with then the dissociation of tartrazine may be sufficiently reduced   and no more crystal formation occurs??