Making ampicillin solution - Ampicillin trihydrate not dissolving (Jul/24/2009 )

Hi all,

I am trying to dissolve ampicillin trihydrate in distilled water at a concentration of 50mg/ml.

I wanted to prepare 50ml of ampicillin solution. So I used 2.5gm of ampicillin to dissolve in distilled water.I made it upto 50 ml.

But I have difficulty dissolving it. It remains as a ilky white solution and after few mins I can see the precipitation (remains insoluble).

Is there a solution for this?

Regards
MS

I the ampicillin stock too old?

miraclestrain on Jul 24 2009, 01:00 PM said:

Have you adjusted the pH see if that helps?

Normally the sodium salt is used in making stock solutions. The trihydrate is soluble only at 10 mg/ml, while the sodium salt is soluble at more than 50 mg/ml. Add NaOH to form the sodium salt and it should go into solution. Next time order the sodium salt.

Hi there,

Thanks, it did work as you told, can you be bit more specific about the sodium salt? Say if you were given ampicillin trihydrate what will add to make a concentration of 50mg/ml?

thanks

1 mole of ampicillin trihydrate needs 1 mole of NaOH to form the sodium salt. Determine the molarity of the 50 mg/ml solution (I don't off hand know the MW of ampicillin trihydrate), and add sufficient 1 M NaOH solution to form the sodium salt. Do this at below final volume, and top up the volume to its final value.