Protocol Online logo
Top : New Forum Archives (2009-): : General Lab Techniques

Convert unit to ul - (Oct/05/2011 )

Hi I have a bottle of IL-2 cytokine from R&D system (402-ML) and it is 20ug. I need to calculate how much I need to get 100 U/mL. Can someone help me please!


After a quick google search, it appears that the definition of a unit of IL2 can vary.

According to this paper (, one unit of IL-2 is approx 3ng. But here ( it says one unit is 10 x the reciprocal value of the 50% activity titre.

So the first thing you need to do is tell us what you are using as a definition of unit.


On the R&D websites. It says the ED50 value is 0.5ng/mL. and its 2.5X10^5 U/ug. Thank you!


Ok, so you have 20µg of a sample at 2.5x10^5 U/µg and you need it at 100U/ml. I'm assuming you have it as a lyophilised powder.

Now, think about it. 2.5x10^5 U/µg = 2.5x10^5U in 1µg so in 20µg you have = 2.5x10^5x20 = 50x10^5U

You say you need 100U/ml so you just need to divide your total Units by 100 = 50x10^5 / 100 = 50000ml = 50L

Another way of doing this will be to calculate how many ug you need to have 100U if you know there are 5x10^5U/µg.

100U / 5x10^5U/µg = 0.0005µg

Now, I'm having problems believing that you have to resuspend your sample in 50L and it'll be pretty much impossible to measure 0.0005µg.

Having had a quick look at the R&D website, they recommend reconstituting at 100µg/ml in PBS containing 0.1%BSA.
So, you need to resuspend your 20µg in 200µl for it to be at 100µg/ml.

Following the same logic as above => 100µg/ml x 5x10^5U/µg = 5x10^7U/µl = 5x10^4U/ml from this you can easily prepare your required 100U/ml by diluting 500 fold.

Just used C1V1 = C2V2 to calculate how much you need of this solution to make your 100U/ml.

-almost a doctor-

Thank you for your help. I get it now:)