Mg citrate precipitates?

[Mattias]

Very simple question:

I dissolve 10 grams of trimagnesium dicitrate in 150 ml of deionised water. It is dissolves very easy and forms a clear solution. But the day after the bottle contains a white precipitate. The precipitate seems to be close to insoluble.

Just wonder if any of you have an idea why it falls out and refuses to be redissolved (even after a 1:1 dilution with water)?

thanks!

[nick22]

Mg(OH)2 would be my guess. It is quite insoluble and should form over time in aqueous magnesium salt solutions.

[paulw]

I'll agree with nick22. I worked for a place that made magnesium citrate oral solution per USP. We had one lot we had to market withdraw due to precipitation. For us, we had to make sure the free acid (excess citric) acid to magnesium ratio was of a certain number to prevent the precipitation.

[Don_Hilton]

You have one other acid in the solution if it is left exposed to air. H2CO3 - from CO2 in the air. MgCO3 is insoluable in water. It does dissolve with acid, so as the MgCO3 is formed, there there is an increase in citric acid -until equilibrium is reached.

[Mattias]

Thanks! It seems as the trick would be to add some citric acid then? I will give it a try!

[Mattias]

Hi,

I prepared different solutions of Mg-citrate and adjusted pH to different levels with citric acid. Only solutions with pH < 3.4 stays clear (after a few weeks).

I added sucrose to these solutions in very high amounts (300 g / litre), but I still think it is undrinkable. It is extremely sour. Not sure how to proceed from here...

[paulw]

Most magnesium citrate oral solutions have some sort of added flavoring. Lemon, cherry and grape where what we used. I never actually tasted any of the stuff myself so I can't comment on how well any sourness was masked or if it was present. I also don't remember all that was added to the formula. I do know we used magnesium hydroxide then added citric acid.

[Mattias]

Does anyone know if these are any acids that does not taste as sour as citric acid (at the same pH value)?