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 packaged 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 massive iron per tablet from the label. In a 150-mil beaker, dissolve most of the tablet and 20 ml of 6 molar hydrochloric acid. Next, you'll be heating the solution on a hot plate for about 10 minutes. This ensures that all of the iron is selfed, but do not bring it to a boil. Then, grab a filter through a filtered filter paper into a 100 ml of 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 5 volumetric flasks and using a 10 ml more pipette, put 1 ml of the iron stock in the first, 2 ml of stock in the second, 3 in the third, 4 in the fourth, and 5 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 do decimal points. Next, we'll 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 spectrometer, 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 5 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, wave 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 monochrometer and hitting the detector, which measures the absorbance. Absorbance is directly proportional to the amount of iron present. This is known as beer's law. Knowing this, which of your standard 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 liter. 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!