Hello Puja Sha San

According to the Molecular Weight of the drug,

194.5mg/ml is 1M

So your stock solution 19.4mg/mL is 99.7mM (approximately 0.1M).

Use the formula C1V1=C2V2

C1= Concentration of stock solution (99.7mM (9,97,00,000)nM)

V1 = Volume of stock to be taken (say A ml)

C2 = Required concentration for cell culture studies (250nmol)

V2 = Required volume for cell culture studies 1ml (say)

9,97,00,000nM x A = 250nM x 1ml

Therefore,

A = 2.507 x 10^-6 ml = 2.507 x 10^-3 ul = 0.002507ul

0.002507ul would be too less a volume to be taken. Not possible to pipette such a small volume. So, you dilute your stock solution (19.4mg/ml) by 1:1000 so that you could take 2.5ul form the diluted stock and make up the volume to 1ml with culture media. This will give you 250nM of the drug in 1ml culture media.

Best.