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Peak tailing in NP chiral LC
Posted: Tue May 22, 2018 6:32 pm
by Mike H.
I'm developing a separation for enantiomers and have a general question. I'm using an AD-H column, MP is 85:15:0.1:0.1 n-Hexane:EtOH:ESA:DEA. Compound is l and d-prolinamide. (I know it doesn't have strong UV absorbance). Anyway I obtain separation of R=4.5, but the tailing for the 2 peaks is drastically different (1.3 for L-prolinamide and 4.3 for d-prolinamide). What could cause this fro mirror image isomers? thx
Re: Peak tailing in NP chiral LC
Posted: Fri Jun 29, 2018 1:53 pm
by Mike H.
Turned out a MP blend was the answer. 70:22.5:7.5:.15 Hexane:EtOH:IPA:ESA was the answer. Both isomers are R=2.5, T =1.6 for both. Turns out the LC class I took several years back is still paying off. Thx Tom.
Re: Peak tailing in NP chiral LC
Posted: Sun Jul 01, 2018 5:36 pm
by Multidimensional
The problem you experienced was that you used an acid and base (ESA:DEA) for a modifier in your method. In general, start with a neutral run, than add acid OR base, only if needed. Using DEA or other amines will result in temporary or even permanent surface changes to the column so be careful. When over-used (which we see a lot of novices do), they can result in a failure to reproduce the method.
Re: Peak tailing in NP chiral LC
Posted: Mon Jul 09, 2018 6:46 pm
by Mike H.
I used DEA early in the development because the author of the paper I was reading on ESA said its use along with ESA was complementary. It's not in this case.