## conversion confusion

Debate and discussion of any biological questions not pertaining to a particular topic.

benedictine
Garter
Posts: 12
Joined: Thu Nov 08, 2007 10:35 pm

### conversion confusion

hi, can someone guide me, how do I convert say x ug/ul of stock solution to 25 pmol/ul working solution?
First with x ug/ul; I use the molecular weight to calculate how many moles in that stock solution. After that what do I do to get to the pmol/ul? I am confused with the pmol/ul part.
thank you.

blcr11
Viper
Posts: 672
Joined: Fri Mar 30, 2007 4:23 am
For me, it’s easiest to convert the stock concentration to pmol/microliter first—which is where you were headed, I think. Once you decide how much working solution you’re going to make, the dilution becomes a straightforward application of the good-old volume-concentration relationship, V1 x C1 = V2 x C2.

Let’s say you have a 100 microgram/ml stock solution of something that has a MW of 100 and you want to make 50 microliters of 25 pmol/microliter working solution. (See, when you make up the problem, you get to make it easy on yourself.) Then the stock concentration is 1 micromol/ml. But 1 micromol/ml is the same as 1000 pmol/microliter. (1 micromol/ml = 1 nmol/microliter = 1000 pmol/microliter). Let V1=50 microliter, C1=25 pmol/microliter, C2=1000 pmol/microliter, and V2=?. Solving the dilution volume-concentration relation for V2 and plugging in the numbers gives V2=1.25 microliters, assuming I didn't make any silly arithematic mistakes. You dilute 1.25 microliters of 100 microgram/ml stock to a final volume of 50 microliters to make a working solution of 25 pmol/microliter.

benedictine
Garter
Posts: 12
Joined: Thu Nov 08, 2007 10:35 pm

thanks a lot!
from bene

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