Analysis of Iron by Atomic Absorption Spectrophotometry


Analysis of iron by atomic absorption spectrophotometry In this experiment, the iron content in a
children’s multivitamin will be analyzed using atomic absorption spectrophotometry
(AAS), and compared to the quantity stated on the package label. The label on a bottle of children’s multivitamins
lists the amount of iron present, but can you believe the label? And how can you test the tablet for the amount
of iron? Today we’ll be seeing how accurate these
labels are by testing the actual amount of iron in a tablet. Don’t forget to read the label of the bottle
of vitamins you are testing. To start, get a multivitamin tablet, Remember to record the brand and mass of iron
per tablet from the label. In 150mL beaker dissolve most of the tablet
and 20mL of 6 molar hydrochloric acid. Next, you you’ll be heating the solution
on a hot plate for about 10 minutes. This ensures that all of the iron is dissolved,
but do not bring it to a boil. Then gravity filter through a fluted filter
paper into 100mL volumetric flask And dilute to the mark with deionized water. It will take a while for the tablet to dissolve
in the HCl, so while it is dissolving, You can already prepare your standard iron
solutions. Take five volumetric flasks and using a 10mm
Mohr pipette, Put one mL of the iron stock in the first,
two mL’s of stock in the second, three in the third, four in the fourth, and five in
the fifth Then fill them all to the mark with deionized
water and mix well, make sure to record the exact amount of stock solution you put in
to two decimal points Next, we will prepare a dilute unknown solution
from our dissolved multivitamin. Pour 40 mL of the multivitamin solution into
a small beaker. Then transfer 25 mL using a 25 mL volumetric
transfer pipette Into a 100 mL volumetric flask. Dilute to the mark with deionized water and
remember to mix well. Now, we will be using the AA spectrophotometer,
which is the machine you see here. The AA will measure the absorbance of light
at 372 nanometers. The samples being measured will be a blank
containing deionized water, the five standard solutions, and the diluted unknown vitamin
solution. The AA works on the principle that certain
elements absorb light at certain wavelengths. Inside the AA,
We have a lamp emitting light of a certain wavelength which gets passed through a flame
containing our sample and out the other side, going through a monochromator, and hitting
the detector which measures its absorbance. Absorbance is directly proportional to the
amount of Iron present, This is known as Beer’s law. Knowing this, which of your samples should
have the highest absorbance? Once the experiment is done and you have your
data, You will generate a graph using Excel. The graph will look something like this a
plot of absorbance versus milligrams of iron per litre. Using your standard solutions, you will make
a calibration curve, and from that, using your unknown absorbance you can extrapolate
the unknown milligrams of iron per liter as shown by the dashed line on the graph. This graph is missing some components. What are they? If you need to review how to graph using Excel,
view the instructional video that takes you through this experiment. Have fun!

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