Analysis of Iron by Atomic Absorption
Spectroscopy
Iron is present in the human body in only trace amounts (50 mg/kg in men and 35
mg/kg in women), it is found in many iron proteins such as hemoglobin, myoglobin, the
cytochromes, hemosiderin, and ferritin. Hemoglobin contains 66-70% of the iron found
in the human body while up to 30% is found in storage as hemosiderin and ferritin. Iron
is also found in trace amounts in many enzymes. In hemoglobin and myoglobin iron
functions in the Fe2+ form to bind oxygen. Hemoglobin carries oxygen from the lungs to
areas of the body that need oxygen such as the muscles where nutrients are oxidized to
carbon dioxide and water. Cytochromes contain an iron ion and in respiration accepts
electrons by going from the ferric ion (Fe3+) to the ferrous ion state (Fe2+). These
electrons eventually combine with hydrogen ion (H+) and oxygen to form water.
This experiment is designed to measure the iron content of such a tablet using atomic
absorption spectroscopy.
Standard Calibration Curve
The concentration of several standard solutions of iron concentration is accurately
measured using the atomic absorption spectrometer. The values of Fe2+ concentration will
be in mg Fe/liter. The calibration curve will be used to determine the concentration of
iron in the solution prepared from a vitamin tablet. Taking into account the dilutions in
the preparation of the sample, the number of mg of iron in the tablet will be calculated.
Preparation of Standard Iron Solutions
Using the stock solution which contains 40 mg of Fe2+ per liter, prepare three standard
solutions with known iron concentrations between 0.0 and 2.0 mg/liter (ppm). In order to
achieve the necessary accuracy you will need to measure volumes with pipet and
volumetric flasks.
Sample Determination and Preparation
Iron containing tablet will be dissolved and serial dilutions be made, to make a solution
with a low enough Fe2+ concentration to be read in the atomic absorption
spectrophotometer.
1. Dissolving the tablet.
One tablet of the brand vitamin to be analyzed is placed in a 100 ml beaker covered by a
watch glass and heated to a slow boil with 25 ml of 6 N HCl for 15 minutes on a hot plate
in a hood. The mixture is then diluted slightly with water, and filtered while hot, through
#40 filter paper directly into a 100 ml volumetric flask. After washing the residue with
hot deionized water the filtrate is allowed to cool to room temperature and diluted to the
mark with room temperature deionized water.
2. First dilution of tablet solution.
Using a 5-ml pipet remove a 5.00 mL aliquot of the tablet solution and transfer it to a
100-mL volumetric flask. et solution.
A 10.00 mL aliquot of Add water to dilute to 100 ml.
3. Second dilution of tabl the solution prepared in part 2 is pipetted into a 100-ml
volumetric flask, and the solution is diluted to the mark with water.
Determine the concentration of the standards and the diluted vitamin solution by atomic
absorption.
Determine the number of mg of iron per tablet from your concentration (mg/Fe per liter
of solution).