⚗️ Oxidizability (permanganate index)
In short
Determination of the permanganate index (oxidizability) of water: heating the sample in a boiling water bath with potassium permanganate and sulfuric acid for a fixed time, adding an excess of sodium oxalate and titrating with permanganate. The test is performed according to PN-EN ISO 8467:2001; Range: 0.5–10 mg/l; samples above 10 mg/l are diluted. The procedure comprises 8 steps; it is used for: Water intended for human consumption — 5.0 mg/l O₂, reference method (Journal of Laws 2026, item 748), Drinking water and water for domestic use, natural mineral water, well and table water, water from swimming pools (clause 1), Waste water — reference method for the permanganate index (Journal of Laws 2019, item 1311); for the organic load of waste water the standard recommends COD.
At a glance
- Standard: PN-EN ISO 8467:2001
- Category: Physicochemistry
- Procedure steps: 8
- Range: 0.5–10 mg/l; samples above 10 mg/l are diluted
- Chloride: below 300 mg/l
- Temperature: boiling water bath in which the solutions in the test tubes quickly reach and keep 96–98 °C
Overview
STATUS (as of 29.10.2026). PN-EN ISO 8467:2001 — Polish version, published 23.07.2001, implements EN ISO 8467:1995 and ISO 8467:1993 [IDT]; it replaced PN-C-04578-02:1985. The standard is current — no withdrawal note. ISO 8467:1993 (second edition, which replaced ISO 8467:1986) and EN ISO 8467:1995 are current in the ISO and CEN catalogues, with no newer edition.
DEFINITION AND SCOPE (clauses 1, 3). The permanganate index is the mass concentration of oxygen equivalent to the amount of permanganate ion consumed when a water sample is treated with that oxidant under defined conditions; it is used for the determination of the parameter “oxidizability”. The standard is primarily intended for water for human consumption and domestic use, drinking water, natural mineral water, well and table water, and water from swimming pools. It applies to waters with a chloride concentration below 300 mg/l; samples with a permanganate index above 10 mg/l are diluted before analysis, and the lower limit of the optimum range is 0.5 mg/l.
WHAT IT MEASURES AND WHAT IT DOES NOT (introduction of the standard). The index is a conventional measure of contamination by organic and oxidizable inorganic matter; it is primarily intended for judging the quality of drinking water and raw waters (well and surface waters), and more heavily contaminated waters are analysed after pre-dilution. Reducing compounds such as iron(II) salts, nitrites or hydrogen sulfide contribute to the index, although they are not classified as impurities. The index is not a measure of the theoretical oxygen demand or of the total content of organic matter — many organic compounds are only partially oxidized in this test, and volatile matter that evaporates before the permanganate is added is not included. For the organic load of waste waters, the standard recommends the chemical oxygen demand (ISO 6060). The method is simple and convenient for surveying a large number of samples. In ground waters oxidizability usually does not exceed 3 mg/l O₂; in surface waters in Poland 1.9–24.8 mg/l O₂ has been found.
PRECISION (9.2). Within-laboratory standard deviations: tap water 1.28–1.94 mg/l (six laboratories) — 0.06–0.21 mg/l; various raw and drinking waters 0.23–8.17 mg/l (five laboratories) — 0.05–0.60 mg/l. Total standard deviations in a single laboratory for resorcinol solutions: 1.83 mg/l — 0.10 mg/l, 9.95 mg/l — 0.12 mg/l.
LEGAL REQUIREMENTS. Water intended for human consumption: oxidizability (permanganate index) 5.0 mg/l O₂; the parameter need not be determined when TOC is analysed (Regulation of the Minister of Health of 22 May 2026, Journal of Laws 2026, item 748, Annex 1 Part C Table 2 item 13, note 9). Measurement uncertainty up to 50 % of the parametric value, reference method — PN-EN ISO 8467 (Annex 4 Part B, note 5). PN-EN ISO 8467 is also the reference method for the permanganate index in waste water (Journal of Laws 2019, item 1311, Annex 12 item 15) and the titrimetric method for COD-Mn in the monitoring of surface and ground waters (Journal of Laws 2021, item 1576, Annex 8, indicator 3.2.3).
Method principle
The sample is heated in a boiling water bath with a known amount of potassium permanganate and sulfuric acid for a fixed period (10 min). Part of the permanganate is reduced by oxidizable matter in the sample; the consumed permanganate is determined by adding an excess of oxalate solution, which is back-titrated with permanganate. A permanganate index of 10 mg/l corresponds to a consumption of about 60 % of the permanganate added to the undiluted sample (clause 4, note 1).
Applications
- Water intended for human consumption — 5.0 mg/l O₂, reference method (Journal of Laws 2026, item 748)
- Drinking water and water for domestic use, natural mineral water, well and table water, water from swimming pools (clause 1)
- Waste water — reference method for the permanganate index (Journal of Laws 2019, item 1311); for the organic load of waste water the standard recommends COD
- Monitoring of surface and ground waters — COD-Mn (Journal of Laws 2021, item 1576)
Key parameters
| Parameter | Value |
|---|---|
| Range | 0.5–10 mg/l; samples above 10 mg/l are diluted |
| Chloride | below 300 mg/l |
| Temperature | boiling water bath in which the solutions in the test tubes quickly reach and keep 96–98 °C |
| Time | (10 ± 2) min of heating with acid, then 10 min ± 15 s after adding the permanganate |
| Test portion | 25.0 ml + 5 ml of H₂SO₄ 2 mol/l + 5 ml of KMnO₄ about 2 mmol/l + 5 ml of sodium oxalate 5 mmol/l |
| Result | in mg/l of oxygen, to two significant figures |
Standard
- Standard number
- PN-EN ISO 8467:2001
- Title (PL)
- Jakość wody — Oznaczanie indeksu nadmanganianowego
- Title (EN)
- Water quality — Determination of permanganate index
Step-by-step procedure
-
Sampling and preservation
Immediately after receiving the sample in the laboratory, add 5 ml of 7.5 mol/l sulfuric acid per litre if this was not done in the field — regardless of whether the sample is to be stored. Analyse as soon as possible and not later than 2 days after sampling; if storage exceeds 6 h — in the dark at 0–5 °C. Shake the bottle before withdrawing the test portion (clause 7).
-
Preparation
All test tubes must be perfectly clean. Samples with a high index are diluted so that the result falls within 0.5–10 mg/l (8.1–8.2).
-
Heating with acid
Pipette (25.0 ± 0.25) ml of sample into a test tube, add (5 ± 0.5) ml of 2 mol/l sulfuric acid and mix by swirling gently; place the tube in the boiling water bath for (10 ± 2) min (8.3).
-
Oxidation
Add (5 ± 0.05) ml of permanganate solution of about 2 mmol/l and start timing (8.3).
-
Oxalate and titration
After 10 min ± 15 s, add (5 ± 0.05) ml of 5 mmol/l sodium oxalate solution and wait until the solution becomes colourless. Titrate, while hot, with permanganate solution to a faint pink colour persisting for about 30 s; record the volume V₁ (8.3).
-
Blank test
In parallel, by the same procedure, with 25 ml of water instead of the test portion; volume of permanganate V₀. Retain the titrated solution for the standardization (8.4).
-
Standardization of permanganate
To the solution retained from the blank add (5.00 ± 0.05) ml of 5 mmol/l sodium oxalate solution, reheat if necessary to about 80 °C and titrate with permanganate to a pink colour persisting for about 30 s; volume V₂. It is good practice to leave the titrated solutions in the test tubes until the next determination (8.5, note 4).
-
Calculation
I_Mn = (V₁ − V₀) / V₂ · f [mg/l of oxygen], where f = V₄ · c(Na₂C₂O₄) · M₀ · 1000 / (1000 · V₅); with the values of the standard (V₄ = 5 ml of 5 mmol/l oxalate, M₀ = 16 mg of oxygen per mmol, V₅ = 25 ml) f = 16 mg/l. The result is reported to two significant figures (9.1, clause 10).
Required equipment and apparatus
| Equipment | Example | Indicative price |
|---|---|---|
| Water bath with a rack for test tubes | of sufficient capacity and power to ensure that the solutions in all test tubes quickly reach and are maintained at 96–98 °C, during both the initial heating and the reaction (6.1) | — |
| Test tubes | length 150–200 mm, diameter 25–35 mm, wall thickness 0.5–1 mm; kept exclusively for this determination; new tubes are cleaned by heating with acidified permanganate solution and checked by blank determinations until the values are low and constant (6.2) | — |
| Burette, 10 ml | preferably of the piston type, graduated in divisions of 0.02 ml, conforming to ISO 385-1 (6.3) | — |
| Volumetric flasks, 100 ml and 1000 ml | 6.4 | — |
| Volumetric pipettes, 5, 10, 25, 50 and 100 ml | 6.5 | — |
| Timing | the reaction lasts 10 min ± 15 s from the addition of permanganate (8.3) | — |
Reagents, media and consumables
| Reagent | CAS | Details |
|---|---|---|
| Water | — | distilled, from reverse osmosis or of equivalent purity — not deionized water from an organic ion exchanger. Non-reducing water is prepared by distilling, in an all-glass apparatus, 1 l of distilled water with 10 ml of 2 mol/l sulfuric acid and a small excess of permanganate stock solution, discarding the first 100 ml of distillate; the permanganate consumption in the blank must not exceed 0.1 ml (clause 5, note 2) |
| Sulfuric acid, ρ = 1.84 g/ml (18 mol/l) | 7664-93-9 | 5.1 |
| Sulfuric acid, c(H₂SO₄) = 7.5 mol/l | — | add 420 ml of concentrated acid slowly, with continuous stirring, to 500 ml of water, cool and dilute to 1 l — for preserving samples (5.2) |
| Sulfuric acid, c(H₂SO₄) = 2 mol/l | — | add 110 ml of concentrated acid slowly, with continuous stirring, to about 500 ml of water; add permanganate solution of about 2 mmol/l slowly until a faint pink colour persists, cool, dilute to 1 l and mix (5.3) |
| Sodium oxalate, stock solution c(Na₂C₂O₄) = 0.05 mol/l | 62-76-0 | dry sodium oxalate at 120 °C for 2 h; dissolve 6.700 g in water in a 1000 ml flask and make up to the mark; stable for 6 months in the dark (5.4) |
| Sodium oxalate, standard volumetric solution 5 mmol/l | — | dilute (100 ± 0.25) ml of stock solution to 1000 ml; stable for 2 weeks (5.5) |
| Potassium permanganate, stock solution about 20 mmol/l | 7722-64-7 | dissolve about 3.2 g of KMnO₄ in water and dilute to 1000 ml; heat at 90–95 °C for 2 h, cool, store for at least 2 days, decant the clear solution and store it in a dark bottle (5.6) |
| Potassium permanganate, volumetric solution about 2 mmol/l | — | dilute 100 ml of stock solution to 1000 ml; relatively stable for several months if stored in the dark; its exact concentration enters the calculation through the standardization in 8.5; commercially available ready-made solutions may be used (5.7, note 3) |
Health and safety (OHS)
- Concentrated sulfuric acid is added to water slowly, with continuous stirring (5.2, 5.3)
- The standard gives no other warnings — handle potassium permanganate, sodium oxalate and hot solutions from the boiling water bath in accordance with their safety data sheets and laboratory practice
Frequently asked questions
Which standard describes this test?
The test is performed according to PN-EN ISO 8467:2001 — “Water quality — Determination of permanganate index”.
How does this method work?
The sample is heated in a boiling water bath with a known amount of potassium permanganate and sulfuric acid for a fixed period (10 min). Part of the permanganate is reduced by oxidizable matter in the sample; the consumed permanganate is determined by adding an excess of oxalate solution, which is back-titrated with permanganate.
What is the measuring range and accuracy?
Range: 0.5–10 mg/l; samples above 10 mg/l are diluted; Chloride: below 300 mg/l; Temperature: boiling water bath in which the solutions in the test tubes quickly reach and keep 96–98 °C; Time: (10 ± 2) min of heating with acid, then 10 min ± 15 s after adding the permanganate.
How long does the test take?
The procedure comprises 8 steps. The standard does not give a duration for every stage — the laboratory's own procedure decides.
What equipment is required?
Water bath with a rack for test tubes, Test tubes, Burette, 10 ml, Volumetric flasks, 100 ml and 1000 ml, Volumetric pipettes, 5, 10, 25, 50 and 100 ml, Timing.
Where is this test used?
Water intended for human consumption — 5.0 mg/l O₂, reference method (Journal of Laws 2026, item 748); Drinking water and water for domestic use, natural mineral water, well and table water, water from swimming pools (clause 1); Waste water — reference method for the permanganate index (Journal of Laws 2019, item 1311); for the organic load of waste water the standard recommends COD; Monitoring of surface and ground waters — COD-Mn (Journal of Laws 2021, item 1576).
What safety precautions apply?
Concentrated sulfuric acid is added to water slowly, with continuous stirring (5.2, 5.3); The standard gives no other warnings — handle potassium permanganate, sodium oxalate and hot solutions from the boiling water bath in accordance with their safety data sheets and laboratory practice.
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-EN ISO 8467.