# simple dilution calculations please help! - how do i determine the concentration in my initial sample? (Jun/29/2009 )

Hi,

I'm using a GCMS machine and the concentration which comes out is in pmol/uL. This doesn't take into account how much sample you added and the final concentration of your sample after preparation. here is my procedure - i diluted my sample by a factor of 2 and then i took 50uL of this and added it into a tube which was then dried in a speed vac. then i added 250uL of toluene (final volume). the GCMS machine then took 1uL of this solution and produced a concentration of about 4pmol/uL. so how do i calculate what the concentration would be in pmol/uL in my original sample?
hope this makes sense.

any help would be appreciated

-themoon-

you have 4 pmol/無 in the machine, you have 4 pmol/無 in 250 無 of toluene.
these 250 無 toluene come from a 50 無 solution. It's like if you diluted your 50 無 solution 5 times.
Then the concentration in 50 無 is 20 pmol/無
this is your sample diluted 2 times
Then your sample was 40 pmol/無

an other way would be to say that you have in250 無 of a 4pml/無 solution : 250*4 = 1000 pmoles
before the dry, you had 1000 pmoles in 50 無
these 1000 pmoles come from 25 無 of sample (you diluted your sample 2 times)
1000/25 = 40 pmol/無

-little mouse-

Agree.

-HomeBrew-

little mouse on Jun 29 2009, 06:55 AM said:

you have 4 pmol/無 in the machine, you have 4 pmol/無 in 250 無 of toluene.
these 250 無 toluene come from a 50 無 solution. It's like if you diluted your 50 無 solution 5 times.
Then the concentration in 50 無 is 20 pmol/無
this is your sample diluted 2 times
Then your sample was 40 pmol/無

an other way would be to say that you have in250 無 of a 4pml/無 solution : 250*4 = 1000 pmoles
before the dry, you had 1000 pmoles in 50 無
these 1000 pmoles come from 25 無 of sample (you diluted your sample 2 times)
1000/25 = 40 pmol/無

Wow, I didn't know how easy it was! Your explanation was perfect! Thank you so much, I understand it so much better now!

-themoon-

HomeBrew on Jun 29 2009, 06:58 PM said:

Agree.

Thanks also for the confirmation

-themoon-