[josicosta]

Hi everyone.

I am currently carrying out an ID test on a Silicon Dioxide sample using the USP method. In the method I am asked to use an Ammonium Molybdate TS that, again according to their method, should be prepared using Molybdic Acid. The problem is in the lab I've only got Ammonium molybdate (VI) tetrahydrate.

(The first step of the same method is dissolving the acid in ammonium hydroxide. If I am not wrong, that in simple terms means getting an aqueous solution of the Ammonium Molybdate salt)
Does anyone know how to get to the acid using the salt, or whether I can replace the acid by the salt and in this case how much should I use of it?

Thanks for any help.

[Arkcon]

No.

Sorry to be curt, but if you're telling people that you're following the USP, then  ... you have to follow the USP.  You will simply have to purchase the correct reagent, and use it.  Even though, logically, you can get there by some other method.

If the USP method is just a convient method for you, then you could do what you suggest, and see if it works.  But in any case, either defined USP testing, or not, if you're making a change, you should validate then change.

[josicosta]

Yes, you are right. Had that ordered already, but meanwhile was just wondering whether there'd be a way, using USP methods, to prepare such acid.

Thanks for your input.

[Arkcon]

By all means, check the USP, to see if they offer an alternative method.  From time to time they do.