Calculating Iron (Fe) PPM from mL Lab Sample

[Puchinita5]

Homework Statement

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!

 

[Ygggdrasil]

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?

 

[Puchinita5]

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 ?

 

[Ygggdrasil]

Yes, that is correct.