This document describes a method to estimate the iron content in a sample using 1,10-phenanthroline. Iron (II) forms an orange-red complex and iron (III) forms a yellow complex with the reagent. Both complexes can be determined by measuring absorbance. A test sample is made acidic and reacted with the reagent. Absorbance at 396nm gives total iron while 515nm gives iron(II). Standards of known iron concentration are prepared and a calibration curve of absorbance vs. concentration is generated. The curve is used to determine the iron concentration in unknown samples from their absorbance.

1. ESTIMATION OF IRON

2. • Iron content in the sample can be determined by
complexing with 1, 10-phenanthroline.
• Iron (II) forms an orange red color complex [Fe
(C12H8N2)3]2+
• iron (III) forms yellow color complex with the same
reagent [Fe (C12H8N2)3]3+.
• Both iron (II) and (III) can be determined from the
absorbance of the complexes.

3. PREPARATION OF TEST SAMPLE
test sample containing
both iron (II) and (III)
is made slightly acidic
with sulphuric acid
treated with 1, 10-
phenanthroline
reagent
buffered to pH 3.9
with potassium
hydrogen phthalate
absorbance at 396 nm
gives the total amount
absorbance at 515 nm
is due to iron (II)
complex alone

4. PREPARATION OF STANDARD
series of standard
solution of ferrous
ammonium sulfate with
varying concentrations
buffering the solution
with 0.2 M sodium
acetate
reacting with 0.25%
solution of 1, 10-
phenanthroline
monohydrate
measuring the
absorbance at 515 nm

5. CALCULATION OF UNKNOWN CONCENTRATION
• Prepare a plot of absorbance versus concentration
of the known solutions (express the concentration in
mg of solution).
• Draw the best fitting straight line through the points
– this is called the Beer-Lambert Law plot
• Place the best Absorbance value of each unknown
solution onto this plot and determine their
concentrations.
• Calculate the amount of iron in the unknown
sample. Express this as mg of Fe per litre of the
original unknown solution

6. MODEL TABULATION

7. CALIBRATION CHART
Standard
Sample
Concentration of test
sample

8. • The calibration chart of measured absorbance as
a function of iron concentration is linear
• concentration of iron in the test sample is
determined graphically.
• The iron (II) complex is quite stable and the
intensity of orange-red color is independent of pH
in the range 2-9, and hence is used for
spectrometric measurements.
• Any iron (III) that may be present is reduced to
iron (II) with hydroxylammonium chloride