# simple dilution calculations please help! - how do i determine the concentration in my initial sample? (Jun/28/2009 )

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

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

Agree.

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

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!

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

Thanks also for the confirmation