Advertisement
If you have a new account but are having problems posting or verifying your account, please email us on hello@boards.ie for help. Thanks :)
Hello all! Please ensure that you are posting a new thread or question in the appropriate forum. The Feedback forum is overwhelmed with questions that are having to be moved elsewhere. If you need help to verify your account contact hello@boards.ie

Question About Working Stocks and Dilution

Options
  • 26-04-2013 8:04pm
    #1
    Ziycon
    Registered Users Posts: 1,987 ✭✭✭


    I'm getting a bit confused with a problem I'm trying to solve.

    I have a sample of DNA that has a conc of 238.2ng/ul, I need 20ul of sample that contains 20ng/ul.

    I was told to make a working stock by diluting 1ul of DNA into 24 ul of water to give me a stock of 10ng/ul

    I was then told that if i took 1ul of the above stock i would have 10ng/ul and if I took 2ul I would have 20ng/ul etc...

    Therefore if I took 20ul I should have 200ng/ul....?
    which I added to 180ul of water to do a 1 in 10 dilution....

    This is were I get confused:

    Does this give me a stock of 200ul of 20ng/ul OR 200ul of 200ng/ul

    Also if I take 20ul from the above correct solution would it give 20ng/ul??

    If anyone can help point me in the right direction i would be so greatful as i've spent the past two days trying to figure it out and I'm pure stumped.


Comments

  • Options
    #2
    Tree
    Moderators, Science, Health & Environment Moderators Posts: 4,710 Mod ✭✭✭✭Tree


    Your working stock is 10ng/uL, however you want a final concentration that is double that (20ng/uL).

    Consider making up another working stock, with a higher concentration (perhaps double what you were going to make).



    ======

    If you took 20uL of your 10ng/uL stock, you would have 200ng in the 20uL you took (which, you can work out is still 10ug/uL of final concentration)

    A one in ten dilution of this is 1ng/uL.


  • Options
    #3
    Dingle_berry
    Registered Users Posts: 885 ✭✭✭Dingle_berry


    We were taught a formula by a lecturer, then told by another lecturer that it was useless!
    It's (Required concentration X Volume) / original concentration or (RxV)/O
    R=20ng/ml
    V=20ul=0.02ml
    O=238.2ng/ml

    Gives you 0.0017ml so 1.7ul of your original solution into 20ul of solvent should give you the solution you want. I don't trust the formula though!

    Also in practise pippetting small amounts like 1ul should be avoided as much as possible to ensure accuracy.


  • Options
    #4
    Squeeonline
    Registered Users Posts: 2,559 ✭✭✭Squeeonline


    Dingle_berry wrote: »
    We were taught a formula by a lecturer, then told by another lecturer that it was useless!
    It's (Required concentration X Volume) / original concentration or (RxV)/O
    R=20ng/ml
    V=20ul=0.02ml
    O=238.2ng/ml

    Gives you 0.0017ml so 1.7ul of your original solution into 20ul of solvent should give you the solution you want. I don't trust the formula though!

    Also in practise pippetting small amounts like 1ul should be avoided as much as possible to ensure accuracy.

    The formula works fine (I use this for cell counts) but you omitted that the Volume is the total volume you need. In this case it's 1.7 uL made up to a total of 20 uL with solvent rather than in 20 ul of solvent. It's a small difference in this case, but it could be a big one if you were trying to get a specific concentration.


Advertisement