199
Method Performance
Precision
In a single laboratory, using a standard solution of 2.00 mg/L Fe
and two representative lots of powder pillow reagents with the
instrument, a single operator obtained a standard deviation of
±0.017 mg/L.
In a single laboratory, using a standard solution of 2.00 mg/L Fe
and two representative lots of AccuVac ampuls with the
instrument, a single operator obtained a standard deviation of
±0.009 mg/L Fe.
Estimated Detection Limit (EDL)
The EDL for program 33 is 0.03 mg/L Fe. For more information
on derivation and use of Hach’s estimated detection limit, see
Section 1.
Interferences
Interfering Substances and Suggested Treatments
Interfering Substance Interference Level and Treatment
Calcium, Ca
2+
No effect at less than 10,000 mg/L as CaCO
3
Chloride, Cl
-
No effect at less than 185,000 mg/L.
Copper, Cu
2+
No effect. Masking agent is contained in FerroVer Iron
Reagent.
High Iron Levels Inhibits color development. Dilute sample and retest to
verify results.
Iron Oxide Requires mild, vigorous or Digesdahl digestion (see Sec-
tion 2). After digestion, adjust sample to pH 3-5 with
sodium hydroxide, then analyze.
Magnesium No effect at 100,000 mg/L as CaCO
3
.
Molybdate, Molybdenum No effect at 25 mg/L as Mo.
High Sulfide Levels, S
2-
1. Treat in fume hood or well-ventilated area. Add
5 mL HCl to 100 mL sample in a 250-mL Erlenmeyer
flask. Boil 20 minutes.
2. Cool. Adjust pH to 3-5 with NaOH. Re-adjust volume
to 100 mL with deionized water.
3. Analyze.
IRON, TOTAL, continued
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