experience on lactice acid content

[michelle.zhang]

Dear friends,
I have trouble when I analyze content of lactic acid so need your advices. Two suppliers of our lab decalared their three batch samples have about 90% purity. But three resultes are about 57%. A same run occured in another lab, data are close to these in our lab. But we are feel so strange about that why two different suppliers have so special but same content in their different batch of samples?
Pls check our HPLC conditions and give me something.
ODS column, PH=2.45 0.2mol KH2PO4 buffer, 214nm at UV detector, 0.8 cm3/min.
Michelle

[SIELC_Tech]

Commercial lactic acid has a few oligomers, that is why the specification states 90%, if you have an old bottle of lactic acid you might see even less purity due to further oligomer formation. You can try to hydrolize oligomers (esters of two or more lactic acids binded together) by refluxing it in water with small amount of organic acid.
Here is the method for the separation oligomers

http://allsep.com/makeChr.php?chr=Chr_070

We observed at least 3 oligomers of lactic acid. If you stress test it (heat lactic acid in the oven at 90-110 degrees and vacuum) the ration will change even furter.

[michelle.zhang]

Dear SIELC-TH,
I made a simple sample refluxing under help of acetate acid. Now it is 70% content for the sample that is 57% in last test. And about your information, I have a question, if the vacum is necessory when all kinds of oligomer need to hydrolize? And why? Could any form of oligomer become lactic acid back?
Thank you for your helpful information.
Michelle

[SIELC_Tech]

Michelle,

You need to drive equlibria either by removing water (to obtain more oligomers and oligomers with higher molecular weight) or introducing a lot of water to hydrolize the oligomers back to lactic acid. If you use stronger acid and more water iventually you will get pure lactic acid by hydrolizing oligomers. Keep in mind that this is a reversible reaction and if you decide to isolate lactric acid by removing you will form oligomers again.

[HW Mueller]

If it is feasible in this case to use base for the hydrolysis the reaction will not be reversible as long as base is present.

[michelle.zhang]

I am trying the refluxing conditions. wish get the best.
Michelle