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.

 

[DeeNos]

Hello,

Based on the information provided, it seems like you are on the right track with your calculations. To confirm, you are correct in saying that for every 1 mL of your standard Fe solution, there is 0.04 mg of iron. And since the initial concentration of your standard Fe solution was 40 ppm, this means that for every 0.04 mg of iron, there is 40 ppm. So, for your 10 mL standard Fe sample, there is 0.4 mg of iron (0.04 mg/mL * 10 mL) and this corresponds to 400 ppm (40 ppm/0.04 mg * 0.4 mg).

For your calibration curve, you can use these values to plot your points and determine the equation of the line. Keep in mind that the dilution factor will also need to be taken into account when calculating the concentration of iron in your samples. So for example, if you diluted your 10 mL standard Fe sample to 100 mL, the concentration of iron in that sample would be 40 ppm * (10 mL/100 mL) = 4 ppm.

I hope this helps clarify any confusion you had. Good luck with your lab!