Separating Isomers: Efficient Method for Chemists?

  • Thread starter Thread starter gravenewworld
  • Start date Start date
  • Tags Tags
    Separation
Click For Summary

Discussion Overview

The discussion revolves around the challenges and methods of separating isomers in chemistry, particularly focusing on the efficiency of current techniques like silica gel columns and LC/MS analysis. Participants explore various alternatives and improvements to streamline the separation process.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant expresses frustration with the tedious process of separating isomers using silica gel columns and LC/MS, highlighting the time-consuming nature of evaporating fractions and preparing samples.
  • Another participant suggests experimenting with different solvent systems and solid phases, such as alumina and Florisil, to improve separation efficiency.
  • There is a proposal to consider using GC instead of LC/MS to potentially save time by analyzing aliquots directly from fractions without the need for evaporation.
  • A later reply mentions the use of prep HPLC with an automatic fraction collector that measures UV absorbance, which may offer better separation and efficiency.
  • One participant indicates they must strip down all samples from fractions and primarily uses ethyl acetate/hexane as the eluent, but is open to trying new column types.

Areas of Agreement / Disagreement

Participants present multiple competing views on the best methods for isomer separation, with no consensus reached on a single approach. Suggestions vary widely, indicating differing opinions on efficiency and practicality.

Contextual Notes

Participants mention specific techniques and equipment availability, such as the necessity of using MS in conjunction with GC, and the limitations of their current setups, which may affect the proposed solutions.

Who May Find This Useful

Chemists and researchers involved in organic synthesis, particularly those working with isomer separation and looking for more efficient methods in analytical chemistry.

gravenewworld
Messages
1,129
Reaction score
27
is any other chemist on here familiar with trying to separate isomers? I hate how tedious it is, after I run a silica gel column, I have to take each fraction evaporate the eluent, dissolve what is left behind in methanol, prepare LC/MS sample, and wait 3.2 min for each sample to run in order to find out which fractions have the isomer i don't want. This is extremely tedious and time consuming when you have about 80+ fractions all for the same compound. you can't see the isomer separate on TLC (the spots will just loot like one spot) so LC/MS is the only way I know of so far that will work. Does anyone on here have a trick up their sleeve and know a more efficient and time saving method to figure out which fractions contain the unwanted isomer?
 
Chemistry news on Phys.org
Well, it could be worse. At least your LCMS run is fast.

Have you tried a lot of solvent systems? What about different solid phases (alumina, Florisil)? That might get you enough separation.

Do you really have to strip down all of the fractions? What about using GC instead? That might save a lot of time.

What about prep HPLC? Our lab has a prep HPLC that has an automatic fraction collector and measures the UV absorbance of everything that comes off of the column. You can usually get better separation with that too.
 
I will have to bug our analytical chemist so I can use the GCMS machine. He doesn't let anyone use it. Other than that, yeah I really do have to strip down all the samples I take from the fractions. I mostly use a ethyl acetate/hexane eluent for the columns that I do because it seems to work the best. The columns I used are also prepacked (i just load the column and put it on the ISCO machine that basically does everything else for me), so the company only has loads of silica gel ones. I will see if i can order alumina and florisil columns too. Thanks again.
 
That much automation and you're still complaining?! :)

If you could use GC then you might be able to just take an aliquot from each fraction and shoot it on the GC without having to strip it down.

Do you need the MS part? You might be able to do it with just regular GC.
 

Similar threads

  • · Replies 2 ·
Replies
2
Views
3K
Replies
11
Views
7K
Replies
1
Views
4K
  • · Replies 4 ·
Replies
4
Views
3K