Chromatography Forum

Hello everybody,
I'm new in this forum. I am a PhD student and I have a problem with evaluating some chromatograms. I hope you can help me.
I'll explain the problem: I have to analyze a sample in which there is a carboxylic acid, a lactone and the 4-hydroxy pentanoic acid. Not having the standard of 4-hydroxy pentanoic acid and having two very close peaks, I'm not sure of good separation.
The lactone comes out at 9.02min and the hydroxypentanoic at 8.63min.
given the situation I can definitely confirm that 8.63 is the hydroxy and not the lactone?
Thank you so much

It will depend on the stability of your retention times. You can inject the standard 10 times and take the standard deviation of the retention times and use a 3x sd as the retention time window around the average time and if the know peak is within that window and the questionable peak is outside the window then you can say it is not the known analyte with some confidence.

The best way though is to obtain the last analyte as a known standard to be certain it is what you are looking for, or confirm by GC/MS using the mass spectra.

Thank you so much. I'm grateful.
I have just an other question. It is possible that the one of the two peaks correspond to a structural isomer of my lactone? But when I injected the corrispetiv standard, I have had only one peak.

Thank you so much. I'm grateful.
I have just an other question. It is possible that the one of the two peaks correspond to a structural isomer of my lactone? But when I injected the corrispetiv standard, I have had only one peak.

It is possible. I have seen isomeric pairs make peaks that separate slightly on column and if the sample only contains one isomer you see only one peak or vice versa if the standard is pure and the sample contains both isomers there is an extra peak.