🔬 Manganese in water

Physicochemistry ISO 6333

Overview

STATUS (as of 29.10.2026). ISO 6333:1986 — current in the ISO catalogue, with no newer edition or draft. The standard has not been adopted as a Polish Standard — the catalogue of Polish Standards contains no standard numbered ISO 6333; the Polish title is a working translation. The regulations on waste water (Journal of Laws 2019, item 1311) and on water monitoring (Journal of Laws 2021, item 1576) do not refer to this standard.

SCOPE (clause 1). Total manganese — dissolved, suspended and organically bound — in surface water and drinking water, at concentrations of 0.01–5 mg/l; higher concentrations after suitable dilution of the sample. The method is not applicable to highly contaminated waters such as industrial waste water.

MANGANESE IN WATER. In water containing oxygen most of the manganese is present in undissolved forms, often associated with microorganisms, and in complexes, e.g. with humic acid; in oxygen-free or strongly acidic water all manganese is dissolved (introduction of the standard). Manganese(II) compounds predominate in ground waters; 0.01–4.08 g Mn/m³ has been found in ground waters in Poland. Manganese in tap water does not endanger health, but causes black deposits and stains.

INTERFERENCES (clause 8). Iron(II) forms a violet complex with formaldoxime. Adding EDTA and the hydroxylammonium chloride/ammonia solution reduces this interference, but the best way is to add a constant, known amount of iron(II) (as ammonium iron(II) sulfate) to every calibration solution, blank and test solution. 1 mg/l of cobalt gives a response equivalent to 40 µg/l of manganese. In the presence of calcium, orthophosphate above 2 mg P/l causes low results, and calcium plus magnesium above 300 mg/l in total cause high results. Turbidity after formation of the complex is removed by centrifuging before the absorbance is measured.

PRECISION (7.2, interlaboratory trial of 1982, 30 results each). E.g. 0.050 mg/l — mean 0.049 mg/l, standard deviation 0.0035 mg/l; 1.000 mg/l — 1.01 and 0.04 mg/l (laboratory A) and 1.001 and 0.0091 mg/l (laboratory B); 4.000 mg/l — 4.02 and 0.047 mg/l (A) and 4.198 and 0.1333 mg/l (B).

LEGAL REQUIREMENTS. Water intended for human consumption: manganese 50 µg/l (Regulation of the Minister of Health of 22 May 2026, Journal of Laws 2026, item 748, Annex 1 Part C Table 2 item 5); measurement uncertainty up to 30 % of the parametric value (Annex 4 Part B).

Method principle

A formaldoxime solution is added to the test portion; manganese forms an orange-red complex whose absorbance is measured at about 450 nm — at the absorption maximum (molar absorption coefficient 11 × 10³ l/(mol·cm)). The complex is stable between pH 9.5 and 10.5, the colour intensity is proportional to the amount of manganese, and the relationship between absorbance and concentration is linear up to 5 mg/l. Suspended or organically bound manganese requires a pretreatment that converts it into forms capable of reacting with formaldoxime — oxidation with peroxodisulfate (clause 2, 6.2).

Applications

• Water intended for human consumption — manganese 50 µg/l (Journal of Laws 2026, item 748)
• Surface waters (clause 1)
• Total manganese, including suspended and organically bound manganese — after pretreatment (6.2)
• Not for highly contaminated waters such as industrial waste water (clause 1)

Key parameters

Standard

Standard number

ISO 6333:1986

Title (PL)

Jakość wody — Oznaczanie manganu — Metoda spektrometryczna z formaldoksymem

Title (EN)

Water quality — Determination of manganese — Formaldoxime spectrometric method

Step-by-step procedure

1. Sampling and preservation

   Container of polyethylene, PVC or glass; acidify the sample with 3 mol/l sulfuric acid to pH approximately, but not less than, 1 — this minimizes adsorption of manganese on the container walls and assists the dissolution of colloidal and particulate forms (clause 5).

2. Test portion

   50 ml of the acidified sample, or an accurately measured smaller aliquot diluted to 50 ml, containing less than 0.25 mg of manganese (6.1).

3. Pretreatment

   If organically bound or suspended manganese is present, add (225 ± 25) mg of oxidizing reagent to the test portion and: a) autoclave for 30 min in a bottle, cool and add about 0.5 g of sodium sulfite, or b) boil for about 40 min in a 100 ml conical flask or beaker, cool, transfer to a 50 ml volumetric flask, make up to the mark and add about 0.5 g of sodium sulfite. Autoclaving is preferable for samples containing humic acids; the pretreated sample may be kept overnight. Pretreatment destroys turbidity and colour; if experience shows that it is not required (e.g. in most cases for drinking water), it may be omitted (6.2).

4. Colour development

   Add 1 ml of ammonium iron(II) sulfate solution and 2 ml of EDTA solution, mix, add 1 ml of formaldoxime solution and immediately 2 ml of sodium hydroxide solution (2.5 ml if the sample has been pretreated). Mix thoroughly, allow to stand for 5–10 min, then add, while mixing, 3 ml of the hydroxylammonium chloride/ammonia solution and leave to stand for at least 1 h (6.4.2, 6.5.1).

5. Measurement

   Between 1 and 4 h after colour development, measure the absorbance at 450 nm against water; cells of 100 mm for the range 0–0.5 mg/l, 10 mm for the range 0–5 mg/l (6.4.3, 6.5.2).

6. Blank test

   In parallel, with 50 ml of water instead of the test portion; if its absorbance differs significantly from the extrapolated absorbance of the zero member, the reasons must be investigated (6.3).

7. Calibration

   Range A (0–0.5 mg/l): dilute 5 ml of standard solution to 1000 ml and put 0, 10, 20, 30 and 40 ml of it into 50 ml flasks — 0; 0.1; 0.2; 0.3 and 0.4 mg/l. Range B (0–5 mg/l): 50 ml of standard solution to 1000 ml and the same volumes — 0, 1, 2, 3 and 4 mg/l. Colour is developed as in step 4. The graph must be linear; the calibration factor f is the reciprocal of the slope (it may also be calculated by regression), and the intercept on the ordinate is the extrapolated absorbance of the zero member. The graph is checked periodically, especially when new reagents are used (6.4).

8. Calculation

   ρMn = f · (A₁ − A₀) · g mg/l, where A₁ is the absorbance of the test solution, A₀ the extrapolated absorbance of the zero member and g = V₁ / V₂ (50 ml / volume of the aliquot taken); the volume of acid added to the sample is taken into account. Results to the nearest 0.01 mg/l in the range 0.01–1 mg/l and to 0.1 mg/l above 1 mg/l (clause 7).

Required equipment and apparatus

Reagents, media and consumables

Health and safety (OHS)

• The formaldoxime solution, the 6 mol/l hydroxylammonium chloride solution and its mixture with ammonia are special hazards — hazardous operations are carried out in a fume cupboard (warning in clause 3)
• Avoid ingestion and inhalation of vapours and protect hands, eyes and face — gloves and goggles must be worn and any skin contamination washed off immediately; inhalation of formaldehyde and formaldoxime vapours causes severe irritation and oedema of the upper respiratory tract (clause 3)
• Toxic gases may be released when samples are acidified (clause 5)

Frequently asked questions