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Experiment Calculations

  • 18-09-2008 09:11PM
    #1
    IrishKnight
    Registered Users, Registered Users 2 Posts: 922 ✭✭✭


    Having a bit of bother with some calculations I need to do for an experiment, so if you could help me out I would be very happy.

    An absorbance of 1 at 260 nm corresponds to a concentration of 50 μg/mL
    (A 1 mL solution in a 1 cm lightpath with an absorbance of 1 at 260 nm contains 50 μg of DNA.)

    I got a reading of 1.08 which should correspond to a conc of 54 μg/mL

    1:50=1.08:x
    1*x=50*1.08
    x=54 μg/mL

    I used a 3 ml soln. so would that mean I would have to divide x by 3 to get my real answer?

    Also, to convert μg/mL into mg would I be right in thinking I would have to multiply by say y mL then multiply that by 0.001 to get it into mg?

    Thanks,
    IK


Comments

  • #2
    2Scoops
    Registered Users, Registered Users 2 Posts: 1,845 ✭✭✭2Scoops


    IrishKnight wrote: »
    I got a reading of 1.08 which should correspond to a conc of 54 μg/mL

    1:50=1.08:x
    1*x=50*1.08
    x=54 μg/mL

    I'm fairly sure that calculation can't be valid if you don't have a standard curve. With only one reference point you can't extrapolate - i.e half the absorbance may not necessarily mean half the amount of protein.
    IrishKnight wrote: »
    I used a 3 ml soln. so would that mean I would have to divide x by 3 to get my real answer?

    Probably not, just be mindful that you would have 3 times the total amount of protein at the given concentration. i.e. 1 mL at 50 μg/mL = 50 μg total; 3 Ml at 50 μg/mL = 150 μg/mL total.

    That said, it might throw off the accuracy/relation to the standard if you read a higher volume. Why not just read them in 1 mL solutions?
    IrishKnight wrote: »
    Also, to convert μg/mL into mg would I be right in thinking I would have to multiply by say y mL then multiply that by 0.001 to get it into mg?

    Just divide by 1000 to go from μg/mL to mg/mL, then multiple by the number of mL to get the total number of mg.

    Edit: Both ways are the same thing - nevermind!


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