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Chemistry Forums for Students => Analytical Chemistry Forum => Topic started by: Jamore22 on January 30, 2007, 11:31:32 AM

Title: Possible compounds formed when 3% sodium propionate is pH'd with 75% phosphoric?
Post by: Jamore22 on January 30, 2007, 11:31:32 AM

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.     

Title: Re: Possible compounds formed when 3% sodium propionate is pH'd with 75% phosphoric?
Post by: AWK on January 31, 2007, 02:34:50 AM

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

Title: Re: Possible compounds formed when 3% sodium propionate is pH'd with 75% phosphoric?
Post by: Jamore22 on January 31, 2007, 05:08:45 PM

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?

Title: Re: Possible compounds formed when 3% sodium propionate is pH'd with 75% phosphoric?
Post by: AWK on February 01, 2007, 10:37:59 AM

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.