[grahamp23]

Hi,

I am trying to do a reaction crystallization to produce benzoic acid. The reaction is as follows:


C6H5COONa + HCl==> NaCl + C6H5COOH

The solvent is such that only the benzoic acid will crash out of solution and the sodium chloride produced will remain dissolved. Is there any way that i can use HPLC to build a standard curve to measure the dissolved concentration of benzoic acid during this process. Can HPLC separate the sodium benzoate from the benzoic acid? would their retention times be different depending on the mobile phase I use? The problem is that the benzoate is the sodium salt of benzoic acid and so there is only a slight difference between them.

Thanks,
Graham

[Arkcon]

Here is a link to a reverse phase method using UV detection that is adequate for soft drink analysis, so should be good for your application:  http://www.sid.ir/en/VEWSSID/J_pdf/82220103508.pdf  This looks to me like a touchy analysis, so you may have to follow this procedure very closely to get good results.

[EDIT]

Opps.  I just notice that reference doesn't specify that its looking for the free acid.  However, the detector should see the free acid, and the acid might chromatograph as well or better than the salt on reverse phase.  But generally, analyzing an organic acid and its salt on reverse phase is a problem for HPLC.