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Homework Help: Need help figuring how to maintain constant concentration in my samples!

  1. Sep 30, 2008 #1
    I am performing an experiment where I am spiking my product with various % of CTAB. I have made stock solution of 2% (w/v) CTAB in 40 mM NaCl. I also need to make sure that I maintain the NaCl conentration at 40 mM. The product that the stock solution is being added to doesn't have any NaCl in it to begin with.

    I know how to calculate the amount of 2% CTAB stock solution to obtain my final CTAB concentrations but am at a loss for how to maintain the NaCl at 40 mM in all samples.

    Example: for 1% CTAB in 1 mL of product, I add 1 mL of 2% CTAB stock solution but by doing this I am reducing the NaCl concentration to 20 mM. I can add more NaCl to the mixture but then I end up reducing the CTAB concentration.

    Can someone please help???
  2. jcsd
  3. Sep 30, 2008 #2


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    You need to make a separate stock solution of CTAB - BTW what is this ? - and NaCl. Another choice is to add the NaCl as a solid.
  4. Sep 30, 2008 #3
    CTAB is cetyltrimethylammonium bromide.
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