Hach DR/850, Procedures Manual, Page: 192 / 460

192
Sampling and Storage
Ferrous iron must be analyzed immediately and cannot be stored.
Analyze samples as soon as possible to prevent oxidation of
ferrous iron to ferric iron, which is not measured.
Accuracy Check
Standard Solution Method
Prepare a ferrous iron stock solution (100 mg/L Fe
2+
) by
dissolving 0.7022 grams of ferrous ammonium sulfate,
hexahydrate, in deionized water. Dilute to 1 liter. Prepare
immediately before use. Dilute 1.00 mL of this solution to 100
mL with deionized water to make a 1.00 mg/L standard solution.
Prepare immediately before use.
Run the test using the 1.00 mg/L Fe 2+ Standard Solution by
following either the powder pillow or AccuVac procedure.
Results should be between 0.90 mg/L and 1.10 mg/L Fe
2+
.
Method Performance
Precision
In a single laboratory using an iron standard solution of 2.00 mg/L
Fe
2+ and two representative lots of powder pillow reagents with
the instrument, a single operator obtained a standard deviation of
±0.017 mg/L Fe
2+ .
In a single laboratory using a standard solution of 2.00 mg/L Fe 2+
and two representative lots of AccuVac ampuls with the
instrument, a single operator obtained a standard deviation of
±0.009 mg/L Fe
2+ .
Estimated Detection Limit
The estimated detection limit for program 33 (powder pillows
and AccuVac Ampuls) is 0.03 mg/L Fe. For more information on
the estimated detection limit, see
Section 1 .
Summary of Method
The 1,10-phenanthroline indicator in Ferrous Iron Reagent reacts
with ferrous iron in the sample to form an orange color in
proportion to the iron concentration. Ferric iron does not react.
The ferric iron (Fe
3+ ) concentration can be determined by
subtracting the ferrous iron concentration from the results of a
total iron test.
IRON, FERROUS,
continued