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Ppm of iron from mL ?

  1. Nov 5, 2011 #1
    1. The problem statement, all variables and given/known data

    Hi. I just did a lab where we are to determine the amount of iron present in a vitamin based on its absorbance (after reacting it with hydroquinon and o-phenanthroline) and I am having trouble making a conversion.

    At the beginning of lab, we prepared a " .04 mg/mL = 40 ppm " standard Fe solution.

    For our calibration curve, we made 1 sample using 10 mL of standard Fe mixed with some citrate (to adjust ph i think), 2mL of hydroquinone, and 3 mL of o-phenanthroline and then diluted with water to 100mL.

    Then, samples was made using 5, 2, 1 and 0 standard iron.

    I took absorbances and now need to construct my calibration curve, but I am to use concentration, not mL.

    Let's say, for the 10mL standard Fe sample. Am I supposed to just say that for every mL, there are .04 mg of iron and for every .04 mg of iron it is 40 ppm. So 10 mL is .04*10=.4mg of iron and .4 mg of iron is 400 ppm ?

    is this the correct way to convert?

    So I would have

    1mL std Fe --> 40 ppm
    2mL std Fe --> 80 ppm
    5mL std Fe --> 200 ppm
    10mL std Fe --> 400 ppm

    Is this right? I'm not sure if I need to account for the fact that it was diluted? I'm confused.


    Thank you!
     
  2. jcsd
  3. Nov 5, 2011 #2

    Ygggdrasil

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    Science Advisor

    ppm (parts per million) is a unit of concentration. For water, 1 g = 1 mL, so one part per million is equal to one millionth of a gram per mL (i.e. 1 µg/mL = 0.001 mg/mL).

    Your standard solution has a concentration of 0.04 mg/mL = 40 ppm. You then dilute 10mL of the 40 ppm solution into 100mL total solution. What concentration is this 100mL solution?
     
  4. Nov 5, 2011 #3
    ok, so for the 10mL standard, would it be 4 ppm since it is diluted in 100mL? 10mL * .04mg/mL *(1/100mL)= .004 mg/mL = 4 micro g /mL = 4 ppm ?
     
  5. Nov 6, 2011 #4

    Ygggdrasil

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    Science Advisor

    Yes, that is correct.
     
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