Hello, your retention times increase with chain length of your FA, so I conclude you use reverse phase-HPLC, correct? Usually you always should get one peak with theses compounds because there is no stereo-isomerism. If all conditions are the same, you should check if the compounds are oxidized due to old batch or wrong storage. If the problem is also with fresh compound, you should ask compound provider if the standards might contain regio-isomers (e.g. acid-group not terminal in the molecule). By the way, how do you detect your peaks? MS, UV, radiolabeled ... ? Best Regards, Max

Hi, thanks for your answer. Yes, it's a reverse-phase HPLC. I don't know if it's a problem of degradation of standards, I bought them all in the same time, same label, same storage. Each standard was opened only once to make aliquotes in order not to open again the "main" bottle to avoid contaminations. The detection is done through an UV DAD.

Maurizio

I have no experience with valeric acid, but the stability is individually different in case of polyunsaterated fatty acids for example. The retention time that is shorter than expected supports the hypothesis that oxidization occured. Anyway the molecule is more hydrophilic than expected. Mass spectrometry could give information about that. If you increase compound amount (when using constant injection volume and buffer concentration), both peaks increase?

Unfortunately I don't have access to MS. I gave a look to past analyses and seems like that both peaks increase proportionally with molarity of the sample itself, so maybe next time I'll try to prepare a sample directly from the bottle and as fast as possible. Thanks again !

You could request Lipidomix GmbH Berlin to determine the mass (or even the molecular structure) of the valeric acid peaks. Simply mass detection should be not expensive, and easy shipment without dry ice might be okay to answer this question, I guess.