# basic molarity/curie question

John Philo jphilo at amgen.com
Tue Nov 5 16:37:37 EST 1996

```Otter wrote:
>
> I am trying to figure out the molarity of my reaction.  I am using
> tritiated s-adenosyl-methionine which has a specific activity of 55.1
> Ci/mmol.  I am using 2 micro Ci in my reactions.  How many micro moles is
> that?  Since I am trying to learn how to perform this calculation, can you
> please show me how you come up with the molarity.

To get the total number of moles you divide the number of curies by the
specific activity. To get things in the units you want, first convert
the specific activity from 55.1 Ci/mmol to .0551 Ci/micromol and the
amount you are using to 2E-6 Ci.  Then you have (2E-6 Ci)/(.0551
Ci/micromol) = 3.63E-5 micromol = 3.63E-11 mol

To come up with the molarity, you must divide the number of moles (not
micromoles) by the volume in which this activity is dispersed, in
liters.  If, for example, your sample is 100 microliters then the
molarity is
(3.63E-11 mol) / (1E-4 liter) = 3.63E-7 molar

'Hope this helps.

John Philo, Protein Chemistry
Amgen Inc., Thousand Oaks, CA
jphilo at amgen.com
*** Disclaimer: These are the opinions of the poster not Amgen Inc.***

```