Hi all,
Do you have any idea about benzodiazepine that has longer retention time than diazepam?
I have tried Midazolam, since its molecule seems to me more lipophilic, but its retention time is 6 minutes, and retention time of diazepam is 11.5 minutes.

My conditions are:
Mobil phase: methanol-acetonitrile-potassium dihydrogenphosphate buffer, 0.05M (50:10:40 v/v), adjusted to PH=3.50.
Flow rate: 1.2 ml/min
Column: Lichrospher RP-18 (5microm); 250mm/4mm, Merck.
Wavelength: 200-400nm (I read absorbance of diazepam at 230nm)
Column temperature: 40c
Thank you in advance.
Pavel