🔬 Total iron in water
In short
Spectrophotometric determination of total iron in water using 1,10-phenanthroline method. The test is performed according to PN-ISO 6332:2001; Measurement range: 0.01–5.0 mg/L Fe. The procedure comprises 9 steps (about 31 min in total); it is used for: Drinking water quality control (Journal of Laws 2017 item 2294—limit 200 µg/L), Groundwater monitoring (wells, intakes), Iron removal process control.
At a glance
- Standard: PN-ISO 6332:2001
- Category: Physicochemistry
- Procedure steps: 9
- Total time of stages: 31 min
- Measurement range: 0.01–5.0 mg/L Fe
- Wavelength: 510 nm
- Detection limit: 0.01 mg/L
Overview
Iron is one of the most frequently determined water quality parameters. In natural waters, it occurs mainly in the form of Fe²⁺ (ferrous iron, dissolved) and Fe³⁺ (ferric iron, forming precipitates). Elevated iron concentration (>0.2 mg/L) causes rusty discoloration of water, metallic taste, deposits in installations, and promotes growth of iron bacteria.
The PN-EN ISO 6332 standard describes a spectrometric method for determining iron using 1,10-phenanthroline. The method enables determination of total iron (after reduction of Fe³⁺ to Fe²⁺), total dissolved iron, and dissolved ferrous iron. Application range: 0.01–5 mg/L Fe.
The permissible iron concentration in drinking water in Poland is 0.200 mg/L (Ministry of Health Regulation). Determination required in routine monitoring of drinking water, groundwater, surface water, and wastewater.
Method principle
Fe³⁺ present in the sample is reduced to Fe²⁺ using hydroxylamine hydrochloride (NH₂OH·HCl). The reduced Fe²⁺ ions react with 1,10-phenanthroline, forming a stable orange-red tris(1,10-phenanthroline)iron(II) complex [Fe(phen)₃]²⁺. The complex absorbance is measured spectrophotometrically at 510 nm. Color intensity is proportional to iron concentration (Beer-Lambert law). The reaction proceeds optimally at pH 2.9–3.5 in the presence of excess phenanthroline.
Applications
- Drinking water quality control (Journal of Laws 2017 item 2294—limit 200 µg/L)
- Groundwater monitoring (wells, intakes)
- Iron removal process control
- Surface water testing (rivers, lakes)
- Water control in heating and cooling installations
- Industrial and municipal wastewater testing
Key parameters
| Parameter | Value |
|---|---|
| Measurement range | 0.01–5.0 mg/L Fe |
| Wavelength | 510 nm |
| Detection limit | 0.01 mg/L |
| Accuracy | ±5% in 0.1–5.0 mg/L range |
| Reaction pH | 2.9–3.5 |
| Color development time | 15 minutes |
Standard
- Standard number
- PN-ISO 6332:2001
- Title (PL)
- Jakość wody — Oznaczanie żelaza — Metoda spektrometryczna z 1,10-fenantroliną
- Title (EN)
- Water quality — Determination of iron — Spectrometric method using 1,10-phenanthroline
Step-by-step procedure
-
Sample preparation
Acidify sample with HCl to pH < 2 immediately after collection (stabilization). Filter through 0.45 µm if determining dissolved Fe (do not filter for total Fe).
-
Sample measurement
Transfer appropriate volume of sample (e.g., 50 mL) with pipette to 100 mL volumetric flask. For high concentration samples—dilute.
-
Reduction of Fe³⁺ to Fe²⁺
Add 2 mL of 10% hydroxylamine hydrochloride solution. Mix. Wait 5 min for complete reduction.
-
Buffer addition
Add 5 mL of 10% sodium citrate solution (or sodium acetate) to maintain pH 2.9–3.5. Mix.
-
Phenanthroline addition
Add 5 mL of 0.25% 1,10-phenanthroline solution. Fill to mark with deionized water. Mix and set aside.
-
Color development
Wait minimum 15 minutes for full development of orange-red complex color.
-
Absorbance measurement
Measure absorbance at 510 nm in 10 mm cuvette against blank (deionized water + reagents). Read concentration from calibration curve.
-
Calibration
Prepare calibration curve with min. 5 standards (0–5 mg/L Fe) prepared analogously to samples. Correlation coefficient r² > 0.999.
-
Quality control
Every 10 samples measure control sample (CRM). Perform blank and duplicates. Deviation max ±10%.
Required equipment and apparatus
| Equipment | Example | Indicative price |
|---|---|---|
| UV-VIS spectrophotometer | Hach DR6000, Shimadzu UV-1900i, Agilent Cary 60 | 15,000–60,000 PLN |
| Glass cuvettes 10 mm | Hellma 100-QS, borosilicate optical cuvettes | 50–300 PLN/piece |
| Automatic pipettes (1–10 mL) | Eppendorf Research Plus, HTL Discovery Comfort | 800–2,500 PLN |
| Volumetric flasks (25, 50, 100 mL) | Class A, DURAN / Brand borosilicate | 30–80 PLN/piece |
| Water bath or heating plate | Memmert WNE 10, IKA C-MAG HP 4 | 3,000–8,000 PLN |
| Analytical balance (0.1 mg) | Mettler Toledo ME204, Radwag AS 220.R2 | 5,000–15,000 PLN |
Reagents, media and consumables
| Reagent | CAS | Details |
|---|---|---|
| 1,10-phenanthroline (hydrochloride monohydrate) | 5144-89-8 | 0.25% solution: dissolve 0.5 g in 200 mL water with a few drops of HCl. Store in dark bottle. |
| Hydroxylamine hydrochloride (NH₂OH·HCl) | 5470-11-1 | 10% solution: 10 g NH₂OH·HCl in 100 mL water. Reducing agent—converts Fe³⁺ to Fe²⁺. Prepare fresh weekly. |
| Sodium acetate or sodium citrate | 6132-04-3 | 10% buffer solution: for pH adjustment in 2.9–3.5 range. |
| Concentrated hydrochloric acid (HCl) | 7647-01-0 | For acidifying samples and dissolving phenanthroline. p.a. purity. |
| Iron standard solution 1000 mg/L Fe | 7782-63-0 | Certified CRM (e.g., Merck Certipur). For calibration curve: 0.05; 0.1; 0.5; 1.0; 2.0; 5.0 mg/L. |
| Deionized water | — | Free from iron, conductivity <0.1 mS/m. |
Health and safety (OHS)
- Concentrated hydrochloric acid (HCl)—corrosive, causes severe skin burns and eye damage (H314). Work under fume hood.
- Hydroxylamine hydrochloride—harmful (H302, H312). Use gloves.
- 1,10-phenanthroline—irritating to skin and eyes (H315, H319). Use gloves and glasses.
- Safety glasses, nitrile gloves, and lab coat required.
- Collect waste in chemical waste containers—do not pour down drain.
Frequently asked questions
Which standard describes this test?
The test is performed according to PN-ISO 6332:2001 — “Water quality — Determination of iron — Spectrometric method using 1,10-phenanthroline”.
How does this method work?
Fe³⁺ present in the sample is reduced to Fe²⁺ using hydroxylamine hydrochloride (NH₂OH·HCl). The reduced Fe²⁺ ions react with 1,10-phenanthroline, forming a stable orange-red tris(1,10-phenanthroline)iron(II) complex [Fe(phen)₃]²⁺.
What is the measuring range and accuracy?
Measurement range: 0.01–5.0 mg/L Fe; Wavelength: 510 nm; Detection limit: 0.01 mg/L; Accuracy: ±5% in 0.1–5.0 mg/L range.
How long does the test take?
The times given for the individual stages add up to approximately 31 min. The procedure comprises 9 steps.
What equipment is required?
UV-VIS spectrophotometer, Glass cuvettes 10 mm, Automatic pipettes (1–10 mL), Volumetric flasks (25, 50, 100 mL), Water bath or heating plate, Analytical balance (0.1 mg). Indicative cost of the core instrument (UV-VIS spectrophotometer): 15,000–60,000 PLN.
Where is this test used?
Drinking water quality control (Journal of Laws 2017 item 2294—limit 200 µg/L); Groundwater monitoring (wells, intakes); Iron removal process control; Surface water testing (rivers, lakes); Water control in heating and cooling installations; Industrial and municipal wastewater testing.
What safety precautions apply?
Concentrated hydrochloric acid (HCl)—corrosive, causes severe skin burns and eye damage (H314). Work under fume hood.; Hydroxylamine hydrochloride—harmful (H302, H312). Use gloves.; 1,10-phenanthroline—irritating to skin and eyes (H315, H319). Use gloves and glasses.; Safety glasses, nitrile gloves, and lab coat required.; Collect waste in chemical waste containers—do not pour down drain.
Which laboratory can perform this test?
The test is performed by laboratories accredited to ISO/IEC 17025. On LabCoda you can find them by the standard number PN-ISO 6332.