method for clopidrogrel

[aniket]

hi all,
i am trying to develop an HPLC-UV method for determiantion of Clopidrogrel in wistar rat plasma, i am presently using follwoing HPLC condition

Column-Atlantis, c18, 250x4.6 mm, 5 µ
MP- 10 mM Ammonim Acetate Buffer (pH5):AcN:Meoh (30:65:5)
Flow rate- 1ml/min
Extarction Solvent- TBME:Hexane (80:20)

the probelm witj above method is that althoug peak sahpe, RT are good enouh, but an intefernece is contionuoley observed, which is not diminishing even if i change the Bufer pH. column, i have even tried lots of extraction slovents, and i had to settle for the above combination beacuse of high recovey, i have tried SPE but the interfernce is stiil there, also it has significat area, so can anyone suggest some improvment to the above method that i can do?

solubilty of clopidrogrel is also a problem, i have also checked for carryover there is no carry over, by giving 2 balnk runs after a aqeous injection, there is no carry over, but something fromplasma only, is there any published method for wistarplasma analysis>?
i found out one but is for metabolite of clopidrogrel and is a gredient method, i want an isocratic method

hope somebody willl hlep me

Thanking You in Advance

[Uwe Neue]

What happens if you use methanol or acetonitrile instead of the mixture? Maybe 67% acetonitrile/ 33% buffer for acetonitrile and maybe 75% methanol and 25% buffer for methanol...