# Primer concentration - stupid question - (Jun/04/2013 )

I've odered primers from IDT.

In the IDT FAQ it is suggested to add 10 microliters of water per 1 nanomole to obtain 100 µM concentration. But in my calculations the final concentration is 1µM/µL. Am I wrong somwhere? How can you possibly get micromoles (10-6) from nanomoles (10-9) by dilution?

This is the link to the IDT manual http://www.idtdna.com/pages/support/technical-vault/faq/application-support/storage/faqs/2011/06/01/how-do-i-reconstitute-my-oligos-to-a-10%C2%B5m-concentration-

Thank for help!

-Angrysh-

You are confusing moles with molar. 1 molar (1 M) is 1 mole per liter. The IDT instructions are 1 nanomole per 10 microliters, which is 10**-9 moles/ 10**-5 liters, or 10**-4 molar, or 100 uM.

-phage434-

Thank you!

Now it is clear. So molar concentration is always per liter?

-Angrysh-

Yes, Molar concentrations are always per litre -it's the SI unit. It is a bit of an unfortunate thing that biologists (including myself) have gotten into using the "M" symbol for mol/l as it is quite confusing until you know the convention.

-bob1-