Which method of separation is more preferable, HPLC, NMR or GC for the determination of diatereoselectivity in polar or non-polar aldol products. What are the advantages or disadvantages of HPLC over other methods
NMR is not providing any separation of compounds.
If the compounds are volatile take GC it provides much higher efficiency of separation. If not you need HPLC and chiral stationary phase.
Regards
G
Isiaka might be talking about seeing the separation for identification，not actually the isolation of the diastereomers, I think!
For determination/identification of diastereoselectivity, it may be better to try all to see, NMR may give you a little more detail (for some cases) than HPLC and GC. For publication, you need more data to support/identify your compounds anyway.
So, if Isiaka can get each of isomers in pure form, It is possible to use them as standards for GC or HPLC.
For NMR - I would suggest to read about chiral shift reagents.
regards,
G
Yes, Dr. Boczkai, you are right!
Hope the NMRs of the diastereomers already have enough difference.
Publications available in my RG account describe such separations in Ohrui's clever stereoselective syntheses of bioactive enantiomers of the New World Screwworm sex pheromone. Stereoselective derivatives were constructed that were then separated on non-stereoselective HPLC, recovered, and the "clean" stereoisomers made available.
GC and HPLC are well known separation and quantification technique even up to trace level. GC has limitation as compound should be volatile. Advantage of HPLC over other is that you can separate the diastereromer using chiral column which has good selectivity for both polar and nonpolar compound. While NMR is not separation technique.
There is a crucial difference between diastereoisomers and enantiomers.
Diastereoisomers can be separated by HPLC or GC without the use of chiral stationnary phases or chiral additives to the mobile phase in case of HPLC, because diastereoisomers have physically (and chemically) different properties. They can also be analysed by NMR, without chiral shift reagents.
Enantiomers have the same physical properties, except they rotate polarised light oppositely. For instance the enantiomers of D- and L-lactic acid are mirror images (comparable to your left and right hand, they are not the same, but in a mirror they are). Therefore, to analyse enantiomers you need a chiral environment (chiral stationnary phase in GC or HPLC) or a chiral additive (HPLC) or a chiral shift reagent (NMR).
There exist HPLC detectors which are based on polarised light, which enable for instance the detection of the ratio of the enantiomers in lactic acid (D and L form)
Thank you for all contributions and interventions @ Prof. Shawana Tabassum, Prof. Grzegorz Boczkaj, Prof. Guobing Xiang, Prof. David Arthur Carlson, Prof. Tabrez Shaikh, Prof. Kees Olieman. I will act accordingly.
- Badges
- Science method