Importance of Elution Order in e.e. determination

[Trishia]

Hi there,

We were looking into buying a few Pirkle phase columns from Regis Technologies; mainly Whelk-01 and ULMO (possibly DACH-DNB as well). As some of you may know, these phases are available in both the (R,R) and (S,S)-forms, thus allowing the invertion of the elution order of the enantiomers by simply switching columns. We are told that "this advantage is *essential* when determining enantiomeric purity when the trace enantiomer should elute before the major"... Is this absolutely necessary? I don't understand the statistical basis under this one...

We're mostly inquiring because if we get only one enantiomeric form of each type, we can get a wider variety of columns with our grant than if we get both (R,R) and (S,S) of each.

I mean, quite logically, other types of columns (such as Daicel's cellulose columns) will only lead to one separation, with no inversion of elution possible... So why would it be such an essential advantage in this case?


Just looking for opinions...

Trishia.

[Tobias Jonsson]

A minor peak eluting in the tail of a main component is much harder to integrate correctly for the software, compared to if the minor peak is eluting before. The peak area is easily underestimated with several percent when using a linear skim to set the baseline for a minor peak on a tail. So having the minor peak first is an advantage regardless of column type - not only for e.e. determinations.

One approach would be to not buy both column types before you have indications that the separation looks promising but need to be reversed, saving some of the grant for a possible second round.