If your aim is to make high-resolution banding chromosome in human, the best concentration of Ethidium bromide and of colcemid is 7 ug/ml and 0.02ug/ml, respectively.  They are added to culture medium for last 2 hours prior to the end of 72-hour blood culture. 

Thank for the answer . u mean to say that i need to add Et br  and colcemid in 70 hrs of culture.  first Et br for one hour and then colcemid for another one hour.

It will be great if you let me know the volume need to be added. Thank you

I mean that you should add both Etbr and colcemid at the same time last 2 hours before of the culture.  The concentration of two solutions that I described is final concentration.  Therefore,  you can arrange volumes of two solutions as you like.   

Thank you very much for the answer