[Jamore22]

A fermentate consists of 3.5% propionate and 1% acetate (propionate as sodium salt). Fermentate was pH'd down to 2.5 with 75% phosphoric acid. A new peak at RT 3.54 appeared on the HPLC glucose method (registering as glu, but not glucose). The fermentate was tested at pH 6.5, 6, 5, 4, 3, and 2.5. The mystery compound increased incrementally as the pH decreased.  What are the possible compounds that are formed in this reaction? I have tested for sodium acetate and sodium phosphate wich were not present.     

[AWK]

Look at Pka-s ors Ka-s of propionic acid and phosphoric acid, and all mysteries disappear

[Jamore22]

Thanks for your timely response! As you can tell I am a microbiologist not a chemist. So you are saying that it is dissociated Na+ Prop-? Would the prop still have the same properties, ie. antimicrobial, without adverse effects?

[AWK]

A stronger acid (phosphoric) replaces a weaker one in its salt., and you have a free propionic acid. I do not know a treshold of your HPLC method, but acetic acid should be also detectable.