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Iron (0.10 - 5.00 mg/L Fe)
UniCell™ Test
Scope and Application: For drinking water, raw water, swimming-bath water, waste water and process control
HCPE 159 B / Druckfarbe schwarz / 1
SUMMARY OF METHOD
Iron(II) ions form an orange-red complex with 1.10-phenanthroline.
Any iron(III) ions present in the water sample are reduced to iron(II)
ions by ascorbic acid before the complex is formed. This method
complies with regulations in many countries and therefore can often
be used for reporting purposes. Contact your local Hach distributor
to determine if this method can be used for regulatory reporting
purposes in your country.
SHELF LIFE OF TEST REAGENT
The test reagents are stable at room temperature for 30 months as
indicated by the expiration date on the package.
SAMPLE COLLECTION, PRESERVATION AND STORAGE
Collect samples in acid-cleaned glass or plastic containers. No acid
addition is necessary if analyzing the samples immediately. To
preserve samples, adjust the pH to 2 or less with concentrated nitric
acid (about 2.00 ml per liter). Preserved samples may be stored up
to six months at room temperature. If reporting only dissolved free
iron, filter sample immediately after collection and before adding
nitric acid.
Before analysis, adjust the pH to between 3 and 5 with
5.0 N sodium hydroxide standard solution. Do not exceed pH 5
as iron may precipitate. Correct the test results for volume additions.
INTERFERENCES
The ions listed in the table have been individually checked up to the
given concentrations. Cumulative effects and the influence of other
ions have not been evaluated. There is no interference from:
1000 mg/L: Cl
-
500 mg/L: Ca
2+
100 mg/L: Ag
+
70 mg/L: Cd
2+
50 mg/L: Co
2+
, Zn
2+
, Pb
2+
, CO
3
2-
, Hg
2+
, Cr
3+
, Cr
6+
25 mg/L: Ni
2+
10 mg/L: Cu
2+
5 mg/L: Sn
2+
Higher amounts of copper, nickel, and tin cause high-bias results.
Total iron including undissolved iron and complexed iron can only
be determined after digesting with the Metal Prep Set HCT 200.
(Total iron measuring range 0.12 – 6.00 mg/L).
ACCURACY CHECK
Standard Solution Method
Prepare a 3.00 mg/L Fe standard solution by pipetting 0.30 ml of
1000 mg/L Fe into a 100 ml volumetric flask. Dilute to the
mark with deionized water. Stopper and invert to mix. Prepare this
solution daily. Perform the iron procedure as described.
Standard Addition Method
(a) Measure 100 ml of sample into three mixing cylinders.
(b) Using a pipette add 0.10, 0.20 and 0.30 ml of 1000 mg/L Fe
standard solution to the three samples. Mix well.
(c)
Analyze each sample using the procedure.
The Fe concentration should increase 1.00 mg/L for each
0.10 ml of standard added.
METHOD PERFORMANCE
Precision
In a single laboratory, using a standard solution of 3.00 mg/L Fe and
two representative lots of reagent, a single operator obtained
a standard deviation of +/- 0.15 mg/L on a total of 14 samples.
TIPS AND TECHNIQUES
1. Adjust pH of preserved samples to between pH 3 – 5
before analysis. Water samples with pH < 2 affects the reagent.
2. The outside of the vial must be clean before placing it in the
instrument. Wipe it down with a damp towel, followed by a dry
one.
3. For a proof of accuracy, use the standard solution or standard
addition method. (See Accuracy Check).
4. See your Instrument’s Procedure Manual for instructions on
adjusting the calibration curve if needed.
5.The temperature of the water sample and the sample vial
should be between 15 – 25°C (59 – 77F).
SAFETY
Good safety habits and laboratory techniques should be used
throughout the procedure. Consult the Material Safety Data Sheet
for information specific to the reagents used.
HCT 159
US/GB