DETERMINATION IN WATER ANALYSIS USING THE PHENANTROLINE METHOD: HOW IT WORKS? The phenanthroline method is the preferred standard procedure for the measurement of iron in water at the present time, except when phosphate or heavy metal interferences are present. The method depends upon the fact that 1,10 phenanthroline combines with Fe²+ to form a complex ion that is orange-red in color. The color produced conforms to Beer's law and is readily measured by visual or photometric comparison. Water samples subjected to analysis have usually been exposed to the atmosphere; consequently, some oxidation of Fe(II) to Fe(III) and precipitation of ferric hydroxide may have occurred. It is necessary to make sure that all the iron is in a soluble condition. This is done by treating a portion of the sample with hydrochloric acid to dissolve the ferric hydroxide: Since the reagent 1,10-phenanthroline is specific for measuring Fe(II), all iron in the form of Fe(III) must be reduced to ...
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