Need help in separating a co-eluting peak?

[mimisandhu]

My compound is neutral. I am using Zorbax C18 SB with MP A = 0.025M Ammonium Acetate buffer, MP B = 15 TFA in ACN.
Gradient : Time %B
0 5
8 95
13 95
13.1 5

There is a peak that is coeluting with the parent peak. Can anyone suggest something that will help separate this peak.

Thanks!

[coquim]

HI! may i know what drug are you analyzing?
You say neutral, but may be your compound is neutral in Ph or neutral in charge. why ar you chosing an IPC regeant like tfa?

[mimisandhu]

The compound is neutral in charge.

[coquim]

look, i´m not a pro in hplc topics , i work on it and i´m still learning, however i don´t understand why you´ve choose an ipc regeant if your compound is neutral in charge. We use Ipc regeant when the drug is eluting at early times because is a very polar compound. I´m asking you what drug you are analyzing because you´ve choose a wrong column to do that perhaps. Could you tell us what compound are you testing? have the compound one or more drugs in it?. it´s a little difficult to help you if you dont tell about this, thats all.
Bye.

[Uwe Neue]

The standard approach is to use methanol instead of acetonitrile and see how this changes your C-gram. Then interpolate...

Other things are possible as well: e.g. a switch in column chemistry from a C18 to a packing with an embeeded polar group, such as SymmetryShield RP 18. The expected changes in selectivity are similar for both cases.

[XL]

Can any of the analytes of interest be ionized (or to be charged under certain conditions)? If No, you really don't need buffer or TFA. If Yes, there are various possibilities to solve this. It would be helpful that you can give out a bit more information on the nature of the compounds without revealing proprietary information.