Hach DR/700 Procedures Manual page 271

IRON, TOTAL,
standard deviation when testing zero concentration samples (Adapted
from Analytical Chemistry, 1980, 52, 2242-2249).
Using two representative lots of FerroVer Iron AccuVac Ampuls, the
standard deviation was ±0.012 mg/L Fe
3+
0.014 mg/L Fe .
INTERFERENCES
The following will not interfere below the levels shown:
Chloride
Calcium
Magnesium
Molybdate Molybdenum
A large excess of iron will inhibit color development. A diluted sample
should be tested if there is any doubt about the validity of a result.
FerroVer Iron Reagent Powder Pillows and AccuVac Ampuls contain a
masking agent which eliminates potential interferences from copper.
Samples containing some forms of iron oxide require the mild, vigorous
or Digesdahl digestion (Section I). After digestion, adjust the pH to
between 2.5 and 5 with ammonium hydroxide.
Samples containing large amounts of sulfide should be treated as follows
in a fume hood, or well ventilated area: Add 5 mL of hydrochloric acid
to 100 mL of sample and boil for 20 minutes. Adjust the pH to between
2.5 and 5 with 5 N sodium hydroxide and readjust the volume to 100 mL
with demineralized water. Analyze as described above.
Highly buffered samples or extreme sample pH may exceed the
buffering capacity of the reagents and require sample pretreatment; see
Interferences, pH (Section I).
REAGENT STORAGE
FerroVer Reagent Powder Pillows are stable indefinitely if stored
properly. A cool, dry atmosphere is recommended. The reagent can be
checked by adding the contents of a pillow to about 25 mL of water
containing visible rust (such as a few drops of Rust Suspension). If the
orange color does not form, the reagent should be replaced.
continued
3+
50-21
and the limit of detection was
185,000 mg/L
10,000 mg/L as CaCO
1000,000 mg/ as CaCO
50 mg/L as Mo
3
3