dose-dependant curve (MTT) - (Jul/31/2012 )

I have to perform a dose-dependant curve (by MTT) to see the effect of a chemical on the growth my cancer cell line. The drug that I’ve been given has a concentration of 20ug/ml and a molar mass of 638.

Am I correct that the molarity of this is 31M ? I have a feeling this doesn’t seem right

No, not correct - 20 ug/ml = 20 mg/l or 0.02 g/l. n=mass/molar mass n=0.02 g/638 g/mol = 31 x10^-6 mol/l or 31 umol/l