[anonymous10012]

Hello,

I am working to develop a method for free fatty acid testing in condiments which contain varying concentrations of acetic acid. My question is regarding the fat extraction step which would precede an acid base titration of dissolved lipids in isopropanol. I spoke to a third party about outsourcing the testing, and she assured me that acetic acid would partition into the aqueous phase of a hexane/water system.

Acetic acid appears to be just as miscible with organic solvents as it is with water, so I have a hard time believing that it would partition solely into the aqueous layer. Does anyone have anything to say about this?


Thank you!

[Corribus]

You can find o/w and hxd/w partition coefficients for acetic acid in this paper, table 1:

https://pubs.acs.org/doi/10.1021/acs.est.8b02585

Hexane would be similar to hxd/w coefficient.

One thing you have to keep in mind is that acetic acid exists in both a dissociated and un-dissociated form at equilibrium. Only the un-dissociated form partitions appreciably into the nonpolar phase.

[anonymous10012]

Hi Corribus,

Thank you for your reply.

I don't have access to that paper. Go figure general chemistry comes back for me.

By this rationale though, I would think that water washes could take care of removing the acetic. I tend to solve things experimentally rather than theoretically when possible, but I haven't purchased any of the reagents or equipment yet.

I guess I will just start by performing the same extraction on a water sample with the same theoretical amount of acid and use that for a blank.

I appreciate your input, and welcome any other ideas.

Thanks again.



 

[pgk]

Do not worry and go ahead.
Solubility of acetic acid in hexane is lower than the titration detection limits.
But as you say, you can check it by extracting a standard aqueous solution of acetic acid with hexane, followed by titration of the aqueous phase.
Hint: Do not worry about any slight difference of the detected acetic concentration because you always lose a little something during extractions.

[anonymous10012]

Thank you pgk.