🔬 Manganese in water
In short
Spectrophotometric determination of manganese in water using formaldoxime method. The test is performed according to ISO 6333:1986; Measurement range: 0.01–5.0 mg/L Mn. The procedure comprises 8 steps (about 22–27 min in total); it is used for: Drinking water quality control (Journal of Laws 2017 item 2294—limit 50 µg/L), Groundwater monitoring (wells, intakes), Manganese removal process control.
At a glance
- Standard: ISO 6333:1986
- Category: Physicochemistry
- Procedure steps: 8
- Total time of stages: 22 min–27 min
- Measurement range: 0.01–5.0 mg/L Mn
- Wavelength: 450 nm
- Detection limit: 0.01 mg/L
Overview
Manganese is one of the key drinking water quality parameters. In groundwater, it occurs mainly as Mn²⁺ and can reach concentrations of several mg/L. Elevated manganese concentration (>0.050 mg/L) causes dark water discoloration, brownish-black deposits in installations, unpleasant metallic taste, and promotes growth of manganese bacteria.
The PN-EN ISO 6333 standard describes a spectrometric method for determining manganese with formaldoxime. The method is used for surface and drinking waters. Application range: 0.01–5 mg/L Mn. Samples with higher concentration should be diluted.
The permissible concentration of manganese in drinking water in Poland is 0.050 mg/L (Ministry of Health Regulation). It is one of the most frequently exceeded parameters in groundwater, especially in deep wells.
Method principle
Manganese(II) reacts with formaldoxime (CH₂=NOH, formaldehyde oxime) in alkaline medium (pH ~10), forming an orange complex whose absorbance is measured at 450 nm. Iron interferences are eliminated by adding EDTA and hydroxylamine hydrochloride, which complex Fe³⁺ and Fe²⁺, preventing their reaction with formaldoxime. Hydroxylamine simultaneously acts as a reducing agent, maintaining manganese in Mn²⁺ form.
Applications
- Drinking water quality control (Journal of Laws 2017 item 2294—limit 50 µg/L)
- Groundwater monitoring (wells, intakes)
- Manganese removal process control
- Surface water testing
- Water control in food and beverage industry
- Industrial wastewater monitoring
Key parameters
| Parameter | Value |
|---|---|
| Measurement range | 0.01–5.0 mg/L Mn |
| Wavelength | 450 nm |
| Detection limit | 0.01 mg/L |
| Accuracy | ±5% in 0.05–5.0 mg/L range |
| Reaction pH | ~10 (alkaline medium) |
| Color development time | 10–15 minutes |
Standard
- Standard number
- ISO 6333:1986
- Title (PL)
- Jakość wody — Oznaczanie manganu — Metoda spektrometryczna z formaldoksymem (brak odpowiednika PN-EN)
- Title (EN)
- Water quality — Determination of manganese — Formaldoxime spectrometric method
Step-by-step procedure
-
Sample preparation
Acidify sample with HNO₃ to pH < 2 immediately after collection. Filter through 0.45 µm if determining dissolved Mn.
-
Sample measurement
Transfer appropriate volume of sample (e.g., 25–50 mL) to 50 mL volumetric flask.
-
EDTA addition
Add 1 mL of 5% EDTA-Na₂ solution to mask iron interferences. Mix.
-
Formaldoxime addition
Add 2 mL of freshly prepared formaldoxime solution. Mix.
-
Alkalinization
Add 1 mL NaOH 10 mol/L to achieve pH ~10. Fill to mark with deionized water. Mix vigorously.
-
Color development
Wait 10–15 minutes for full development of orange complex color.
-
Absorbance measurement
Measure absorbance at 450 nm in 10 mm cuvette (or longer for low concentrations) against blank. Read concentration from calibration curve.
-
Calibration and quality control
Prepare calibration curve with min. 5 standards. Perform blank, CRM control samples, and duplicates every 10 samples.
Required equipment and apparatus
| Equipment | Example | Indicative price |
|---|---|---|
| UV-VIS spectrophotometer | Hach DR6000, Shimadzu UV-1900i, HACH DR3900 | 15,000–60,000 PLN |
| Glass / quartz cuvettes 10–50 mm | Hellma, borosilicate cuvettes | 50–400 PLN/piece |
| Automatic pipettes | Eppendorf Research Plus (1–10 mL) | 800–2,500 PLN |
| Volumetric flasks (50, 100 mL) | Class A, borosilicate | 30–80 PLN/piece |
| Analytical balance (0.1 mg) | Radwag AS 220.R2, Mettler Toledo ME204 | 5,000–15,000 PLN |
Reagents, media and consumables
| Reagent | CAS | Details |
|---|---|---|
| Formaldoxime (solution) | — | Prepare fresh: mix equal volumes of 2% formaldehyde and 4% hydroxylamine hydrochloride. Solution unstable—prepare daily. |
| Hydroxylamine hydrochloride (NH₂OH·HCl) | 5470-11-1 | 4% solution: 4 g in 100 mL water. Reducing agent and formaldoxime component. |
| Formaldehyde 37% (formalin) | 50-00-0 | 2% solution: dilute formaldehyde with deionized water. For formaldoxime preparation. |
| EDTA-Na₂ solution 5% | 6381-92-6 | Disodium EDTA salt—for masking iron interferences. 5 g EDTA-Na₂ in 100 mL water. |
| Sodium hydroxide (NaOH) 10 mol/L | 1310-73-2 | For alkalinizing reaction medium to pH ~10. |
| Manganese standard solution 1000 mg/L Mn | 7785-87-7 | Certified CRM (e.g., Merck Certipur) from MnSO₄. For calibration: 0.05; 0.1; 0.5; 1.0; 2.0; 5.0 mg/L. |
| Deionized water | — | Free from manganese, conductivity <0.1 mS/m. |
Health and safety (OHS)
- Formaldehyde (formalin)—carcinogenic cat. 1B (H350), toxic by inhalation (H331), irritating. Work under fume hood!
- NaOH 10 mol/L—strongly corrosive (H314). Causes severe skin burns and eye damage.
- EDTA-Na₂—irritating to eyes (H319). Use safety glasses.
- Safety glasses, nitrile gloves, and lab coat required.
- Formaldehyde-containing waste—collect separately as hazardous waste.
Frequently asked questions
Which standard describes this test?
The test is performed according to ISO 6333:1986 — “Water quality — Determination of manganese — Formaldoxime spectrometric method”.
How does this method work?
Manganese(II) reacts with formaldoxime (CH₂=NOH, formaldehyde oxime) in alkaline medium (pH ~10), forming an orange complex whose absorbance is measured at 450 nm. Iron interferences are eliminated by adding EDTA and hydroxylamine hydrochloride, which complex Fe³⁺ and Fe²⁺, preventing their reaction with formaldoxime.
What is the measuring range and accuracy?
Measurement range: 0.01–5.0 mg/L Mn; Wavelength: 450 nm; Detection limit: 0.01 mg/L; Accuracy: ±5% in 0.05–5.0 mg/L range.
How long does the test take?
The times given for the individual stages add up to approximately 22 min–27 min. The procedure comprises 8 steps.
What equipment is required?
UV-VIS spectrophotometer, Glass / quartz cuvettes 10–50 mm, Automatic pipettes, Volumetric flasks (50, 100 mL), 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 50 µg/L); Groundwater monitoring (wells, intakes); Manganese removal process control; Surface water testing; Water control in food and beverage industry; Industrial wastewater monitoring.
What safety precautions apply?
Formaldehyde (formalin)—carcinogenic cat. 1B (H350), toxic by inhalation (H331), irritating. Work under fume hood!; NaOH 10 mol/L—strongly corrosive (H314). Causes severe skin burns and eye damage.; EDTA-Na₂—irritating to eyes (H319). Use safety glasses.; Safety glasses, nitrile gloves, and lab coat required.; Formaldehyde-containing waste—collect separately as hazardous waste.
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 ISO 6333.