Chromatography Forum

Hello,
I'm interested in using the Prevail Organic Acid column (Alltech) for the separation and detection of long-chain free fatty acids (C16- C20) by HPLC-ELSD. The Alltech application guide shows excellent resolution for a range of these fatty acids in about 10 min, using isocratic 75:25 MeCN/MeOH.

Does anyone have experience with this column? Can any other C18 be substituted? I can't find any info on the particle makeup for these columns anywhere. I'm unwilling to spend out on one if it's a similar phase to something we already have in the cupboard....

And, yes, I'm well aware of the mostly GC techniques for the analysis of fatty acids as FAMEs - but I'm specifically looking for a method for free fatty acid analysis WITHOUT any derivatization.

thanks
Tony

an eluant of water, acetonitrile and a bit of phosphoric acid to surpress dissociation and these acids can be separated on typical C18 and I would suppose C8 columns. We use UV detection at 205 nm if the concentrations are high enough.

Yes, I had thought of that - the only problem is I want to steer clear of phosphoric acid, as I am also trying to get the method to work with negative ESI or APCI/MS detection. So a pure MeCN/MeOH mobile phase, perhaps with some water (as would be needed for efficient ESI but not necessarily APCI) looks most appropriate. Also for this reason I want to avoid TFA as an additive as it will strongly supress negative ESI or APCI.

At the moment I have been method-developing with a LUNA C18(2) column. I have tried additives of high concentrations (up to 0.2%) of acetic/formic acids, but there are only marginal improvements in otherwise quite broad peak shapes. Hence my original question about whether the Prevail column is just another C18 or is there something special about it that makes it particularly suitable for organic acids.

Tony - we have used the Prevail organic acid column and guard for smaller hydroxy acids, using dilute sulfuric acid as eluent and conductivity detection, and it worked fine. We have not tried it with any long-chain fatty acids like you describe, we use GC for those. As to the Luna C18(2) we have only used it for two typical RP applications. For our mixture of analytes, the Prevail column did work better than an organic acid column tried from ThermoKeystone. I tried the Prevail after talking with Alltech; their tech support said the Prevail organic acid column was specifically designed for its purpose, and was a quantum jump better than the ion excluion column we had used in the past for organic acids. I may agree.

Dear Tony:

In the past I have settled an application using a Phenyl column. Maybe you can try it.

C18 is to apolar for free-fatty acids, so you should always have problems with long chain ones.

I am not acquainted with Prevail, but I would guess it is not C18...