ELSD detector

[okara]

Hi,
I am looking for separation of chiral compound (racemic sol) on ELSD detector. I am able to separate them but the both enantiomer is not same in term of area. Can any one explain this. I try to change the temperature and gas flow rate.
the best I got at 20degree and 1.2 ml flow rate. Mobile phase is hexane and methanol.
The first enantiomer is 68% and second one is 23%
Please help me out
Thanks

[Cliff Mitchell]

Assuming that you are not having integration problems...

1. The solution may not be racemic, it may be ~75/25
Did you prepare this solution from two "pure" samples of R and S? If the purity of each is not same, it could explain what you see. Is it a synthetic sample or something bought from a supplier? The solution prior to injection, is there any optical activity you can measure, CD or polarimetry available? If there is measurable optical activity then it is not racemic.

2. You may not have a chiral separation, it may be the separation of the enantiomers and a impurity. Does your compound absorb UV? If so, are the peak areas equal in the UV chromatogram? Does the ratio of the peak areas/heights stay the same at all wavelengths? If they do it is likely that you do have a chiral separation. Run the sample on a C18 or other achiral phase, do you still see peaks of this ratio? If so then you do not have chiral separation.

If you cannot use UV, some other things to try are MS detection (same m/z and frag pattern in MSMS), RI detection (same response/ratio), or get another sample of your compound that is definitely racemic, or inject pure standards of R and S and verify that the peaks are at different times.

It is unlikely that your ELSD detection settings (temp and gas flow) are causing an unequal change in the enantiomers.

Last thing, hexane and methanol, do they mix?