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Pls confirm this idea for me!
Posted: Wed Oct 06, 2004 5:31 am
by michelle.zhang
Every one,
Any conventional column, C18 and C8, could not separate the D-lactic acid and L-Lactic acid, right? I have no any ideas about chiral column.
Thank you in advance.
michelle
Posted: Wed Oct 06, 2004 10:29 am
by tom jupille
Yes, separation of enantiomers requires an enantioselective ("chiral") system. Three possibilities:
- 1. derivatize with with an enantiomerically pure reagent to make diastereomers (which are separable on an achiral column). This is inconvenient, to say the least!
2. Use a chiral additive in the mobile phase. This gets expensive, and can interfere with detection
3. Use one of the many chiral columns available.This is the most common/popular approach.
Posted: Thu Oct 07, 2004 6:32 pm
by Robotjock
If you actually need to separate D-lactic acid and L-Lactic acid the Chirex 3126 penicillamine column offered by Phenomenex will work. They even used lactic acid as one of their example applications as I recall.
regards,
Robotjock
Posted: Fri Oct 08, 2004 12:42 am
by syx
Dear Mr. Tom,
I want to know about chiral additive in the mobile phase. Can you give explanation about them?
Best regards,
SYX
Posted: Fri Oct 08, 2004 2:10 am
by tom jupille
Any chiral compound which can complex with your analyte(s) can be added to the mobile phase. The resulting complex will be diastereomeric; the diastereomers can (hopefully) be resolved. Probably the most commonly used complexing agents have been cyclodextrin derivatives. Although this approach has been used with HPLC, it is not very popular, because it consumes large quantities of expensive reagents.
It has proven more popular in capillary electrophoresis. The following quote is taken from:
http://www.chemsoc.org/chembytes/ezine/ ... _nov00.htm
Chiral separations
Cyclodextrin chemically substituted with sulphate groups
One area where CE has distinct advantages over other separation techniques is chiral analysis. Chiral separations are among the most widely used applications of CE. A chiral substance, usually a cyclodextrin, is added to the buffer. If the enantiomers of the analyte interact differently with the cyclodextrin then a chiral separation is feasible. The hydroxyl groups on the cyclodextrin can be chemically substituted with groups such as methyl, hydroxypropyl or sulphate. The structure below shows the structure of a cyclodextrin that has been chemically substituted with sulphate groups. These sulphated cyclodextrins have different interactions with the analytes and will therefore offer different separation possibilities. The analyst can optimise methods to test the purity of single enantiomer compounds, where a detection limit of 0.1 per cent is often required to determine of the trace level enantiomer impurity.
