Please, help with RNA extraction.

[melia at ar.vhebron.es]

I have problems when I try to isolate total RNA from mouse liver or brain by 
Chomczynsky method, because the two phases I should obtain after adding 
phenol and chloroform doesn't separate during centrifugation. This 
difficults the extraction and makes the efficiency to be very low.Does 
anybody know why this happens and how to avoid? Is this method good enough  
to extract RNA from those tissues?

I would appreciate your comments a lot.
Thank you,

Maria

melia at ar.vhebron.es