By PL on Friday, December 26, 2003 - 04:08 am:
Dear All,
Can we seperate enatiomers with reverse phase to that of using C-8, C-18 columns.
If i have a method to seperate the enatiomers by chiral purity, is it necessary to seperate it by reverse phase in which other impurities are seperated?
By tom jupille on Tuesday, December 30, 2003 - 08:10 am:
"standard" reversed-phase columns (e.g., C18) are not enantioselective. The only way to separate enantiomers on such a column would be to use an enantioselective additive in the mobile phase.
There are many "chiral" (enantioselective) columns available which operate in reversed-phase mode. These columns may also separate achiral impurities, but that is not their primary purpose.
My personal opinion is that unless you are running large numbers of samples (e.g., thousands), the effort required to develop a single method for both purposes is not worth the benefit. I would run two separate methods.
By Anonymous on Friday, January 2, 2004 - 01:23 pm:
Another way to separate enantiomers using conventional non-chiral columns is to derivatize your analytes using an enantiomerically PURE derivatization regent choice of which depends on the chemistry of your analyte. Derivatization will convert the enantiomers into diastereomers which can be then separated using non-chral columns. Lots of literature was published on the subject.
Of course, if you want to use the method for other, achiral impurities, you must make sure that that reagent is also suitable for quantitative derivatization of the impurities. In other words, you must know what the impurities are and select the enatiomerically pure chiral reagent for analyte and impurities or select the reagent for the analyte that does not react with impurities (if the chemistry of impurities is different, very likely). In either case, you must know the chemistry of the impurities. If this is not the case, then I would agree with Tom to use two methods, chiral for the analyte, and achiral for the impurities.
If you use the derivatization, you must also validate the derivatization yields of the enatiomers and the impurities (or prove it is 0 for the impurity) which might be more time-consuming together with optimization of derivatization conditions than using the two method approach mentioned above.
Good luck.
Vladimir.