Chromatography Forum

Hi,

I'm trying to analyze a cyclic ketone using normal phase HPLC-UV and also HPLC-ELSD
with no luck thus far.

Has anybody any suggestions as to conditions that may be suitable

Regards.

Is this ketone volatile? If so, GC or GCMS.

If volatile, you might lose it in ELSD nebulizer.

Hi -
I don't think it's especially volatile- it's isolated by evaporation of a solvent
- I've tried using various Evap and Neb settings but no trace whatsoever
- I do seem to get a trace on the UV at 254 but nothing reproducible

if you molecular weight is below 200 it most likely that you compound is volatile. Inject the compound without column and see if you will observe signal in ELSD. If your compound is not aromatic you will need lower UV (200-210 nm). Why are you using normal phase instead of revered-phase? Your keton is neutral hydrophobic compound (I assume that it has at least 4 carbons) and should be analyzed by RP. In normal phase you probably use alcohol and cutoff is probably 230 nm.

Try injecting a high concentration standard solution of your compound in the solvent you are using onto ELSD without column connected, and have the ELSD gain set high (10) and the temperature set low (~30-35oC). If you don't get a peak for it with these settings, you can figure that you cannot use ELSD for this analysis. If you do get a peak and it is quite large without column attached, then you need to figure out if it is not eluting from column (low recovery).

Also, what temperature do you use to evapourate the solvent to recover your cyclic ketone? If it is fairly low, then maybe the cyclic ketone could still be volatile enough to not be detected by ELSD. I inject samples that include DMSO, and get no peak for DMSO, which has a high boiling point of 189 C with the ELSD temperature set at 70 C. You could estimate the boiling point of your compound using Chemspider.

Thanks for the help everybody.
I think it may be that the compound is too volatile for the ELSD
Thanks again

Most ketones will derivatize pretty easily with dinitrophenylhydrazine (DNPH) under acidic conditions. Separation via reversed phase and detection with UV is then usually possible. This tends to work more quickly with smaller aldehydes and ketones, but I've done it with thujone. Just be careful of molecules with more than one carbonyl and be prepared for a slightly more complex chromatogram.