4 replies to this topic

[themoon]

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

Edited by themoon, 29 June 2009 - 04:00 AM.

[little mouse]

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

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

[HomeBrew]

Agree.

[themoon]

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

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

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

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