Ferrous (Fe++) Test - 1,10-Phenanthroline Method (figs.
2-11 and 2-12, and para 2-18).
(1) Iron in Water.
Natural water contain variable but minor
amounts or iron.
Iron in ground waters is normally present in the
ferrous (Fe++) state which is easily oxidized to ferric (Fe+++) on
exposure to air.
Iron can enter a water system by leaching natural
deposits from iron-bearing industrial wastes, effluents from pickling
or acidic mine drainage.
(a) Iron in domestic water supply systems stains laundry and
procelain, causing more of a nuisance than a potential health hazard.
Taste thresholds of iron in water are 0.1 mg/1 ferrous iron and 0.2
mg/l ferric iron, giving a bitter or astrigent taste.
Water used in
industrial processes usually contain less than 0.2 mg/l total iron.
Domestic water supplies containing more than 0.3 mg/l total iron are
objectionable due to staining and taste considerations.
(b) The Iron, Ferrous, (Fe++) test 1, 10-Phenanthroline Method
is the most well-known test for ferrous and total iron. The 1, 10-
phenanthroline reagent gives an orange color with ferrous iron and is
free from common interferences.
The indicator is combined with a
reducing agent for total iron analysis in a single powder formulation.
The amount of ferric iron present can be determined as the difference
betweem the amount of ferrous iron and the results of a total iron
test paragraph 2-19.c.
The Iron reagent converts all iron present in
the sample to the ferrous state,
including precipitated or suspended
iron such as rust, where it reacts with the 1, 10-phenanthroline to
give the orange color necessary for the determination.
(2) Ferrous Iron (Fe++) Test Procedure.
Samples should be analyzed as soon as possible
after collection to prevent air oxidation of
ferrous iron (Fe++) to ferric iron (Fe+++).
Iron reagent powder pillows are stable up to 12
months depending on storage and handling conditions.
A cool, dry atmosphere is recommended for longest
The iron reagent powder can be
checked by adding the contents of one pillow to
about 25 ml of water containing visual rust. If
the characteristic orange color does not
then the reagent has deteriorated beyond
should be discarded and reordered.
A large excess of iron will inhibit full
A diluted sample should be
if there is any doubt about the validity
To extend the range of the test,
sample dilution is necessary (para 2-10a,