🔬 Ammonium Nitrogen in Water
In short
Manual spectrometric determination of ammonium in water by measuring the blue compound formed with salicylate and hypochlorite in the presence of sodium nitroprusside. The test is performed according to PN-ISO 7150-1:2002 (ISO 7150-1:1984); Range: ammonium nitrogen up to 1 mg/l with a 40 ml test portion; higher concentrations in smaller test portions. The procedure comprises 8 steps; it is used for: Drinking water — ammonium 0.50 mg/l (Journal of Laws 2026, item 748, Annex 1 Part C); where chloramination is used, a group A monitoring parameter (Annex 3), Most raw waters (clause 1), Waste water — PN-ISO 7150-1 is one of the reference methods for ammonium nitrogen (Journal of Laws 2019, item 1311, Annex 12).
At a glance
- Standard: PN-ISO 7150-1:2002 (ISO 7150-1:1984)
- Category: Physicochemistry
- Procedure steps: 8
- Range: ammonium nitrogen up to 1 mg/l with a 40 ml test portion; higher concentrations in smaller test portions
- Limit of detection: 0.003–0.008 mg/l (40 mm cell, 40 ml test portion)
- Wavelength: about 655 nm — the wavelength of maximum absorbance is checked when the method is first used
Overview
STATUS (as of 28.10.2026). PN-ISO 7150-1:2002 — Polish version, published 10.01.2002, implements ISO 7150-1:1984 [IDT]; it replaced PN-C-04576-01:1976. The standard is current — no withdrawal note.
SCOPE (clause 1). A manual spectrometric method for the determination of ammonium in drinking water and in most raw and waste waters. Excessively coloured or saline waters require prior distillation (clause 10). With the maximum test portion of 40 ml, ammonium nitrogen is determined up to 1 mg/l, and in smaller test portions much higher concentrations. The limit of detection with 40 mm cells and a 40 ml test portion is 0.003–0.008 mg/l; 0.200 mg/l of nitrogen then gives an absorbance of about 0.69, and in a 10 mm cell 0.750 mg/l gives about 0.65 (data from an interlaboratory exercise in the United Kingdom).
CHEMISTRY (clause 3). Hypochlorite ions are generated in solution by the alkaline hydrolysis of sodium dichloroisocyanurate; the chloramine formed reacts with sodium salicylate at pH 12.6 in the presence of sodium nitroprusside. Chloramines present in the sample are thus determined quantitatively together with ammonium. Sodium citrate in the reagent masks interference from cations, notably calcium and magnesium.
INTERFERENCES (clauses 9–10). Of the substances tested, only aniline and ethanolamine interfered seriously — this is to be expected from primary amines in general, which are seldom encountered at appreciable concentrations in waters. Extremes of acidity or alkalinity in the sample and substances that reduce hypochlorite interfere with the formation of the coloured compound. In saline samples magnesium precipitates when the complexing capacity of the citrate is exceeded — then distillation according to ISO 5664 is necessary, with the distillate collected in 1 % (V/V) hydrochloric acid; the distillate is neutralized and made up to a known volume.
LOW CONCENTRATIONS (clause 11). The determination of low concentrations is particularly susceptible to bias from traces of ammonium in the analytical environment. The standard requires the absorbances of the blank and of the calibration series (measured against water) to be recorded each time the method is used, and the total standard deviation (with at least 9 degrees of freedom) to be estimated when the method is first used.
DRINKING WATER AND WASTE WATER — LEGAL REQUIREMENTS. Regulation of the Minister of Health of 22 May 2026 (Journal of Laws 2026, item 748): ammonium 0.50 mg/l (Annex 1 Part C Table 2 item 4), measurement uncertainty 40 % of the parametric value (Annex 4 Part B); where chloramination is used, ammonium and nitrite are added to the group A monitoring parameters (Annex 3). The Regulation of the Minister of Maritime Economy and Inland Navigation of 12 July 2019 (Journal of Laws 2019, item 1311) lists PN-ISO 7150-1 among the reference methods for ammonium nitrogen in waste water (Annex 12, item 6).
CONVERSIONS (Table 2). 1 mg/l of nitrogen corresponds to 1.288 mg/l of ammonium and 1.216 mg/l of ammonia; 1 mg/l of ammonium corresponds to 0.777 mg/l of nitrogen.
WHAT WE DO NOT GIVE HERE. We do not reproduce the figures of the precision table (Table 3) or of the tests of the effect of other substances (Annex A).
Method principle
Spectrometric measurement at about 655 nm of the blue compound formed by the reaction of ammonium with salicylate and hypochlorite ions in the presence of sodium nitrosopentacyanoferrate(III) (sodium nitroprusside).
Hypochlorite ions are generated in solution by the alkaline hydrolysis of sodium dichloroisocyanurate, and the reaction of the chloramine with salicylate takes place at pH 12.6. Sodium citrate masks interference from calcium and magnesium; chloramines present in the sample are determined together with ammonium.
Applications
- Drinking water — ammonium 0.50 mg/l (Journal of Laws 2026, item 748, Annex 1 Part C); where chloramination is used, a group A monitoring parameter (Annex 3)
- Most raw waters (clause 1)
- Waste water — PN-ISO 7150-1 is one of the reference methods for ammonium nitrogen (Journal of Laws 2019, item 1311, Annex 12)
- Excessively coloured or saline waters — after distillation according to ISO 5664 (clause 10)
Key parameters
| Parameter | Value |
|---|---|
| Range | ammonium nitrogen up to 1 mg/l with a 40 ml test portion; higher concentrations in smaller test portions |
| Limit of detection | 0.003–0.008 mg/l (40 mm cell, 40 ml test portion) |
| Wavelength | about 655 nm — the wavelength of maximum absorbance is checked when the method is first used |
| Colour development | at least 60 min in a water bath at 25 ± 1 °C; all determinations and calibrations at the same temperature (± 1 K) |
| Reaction pH | 12.6 ± 0.1 |
| Conversion | 1 mg/l N = 1.288 mg/l NH₄⁺ = 1.216 mg/l NH₃ |
Standard
- Standard number
- PN-ISO 7150-1:2002 (ISO 7150-1:1984)
- Title (PL)
- Jakość wody — Oznaczanie azotu amonowego — Część 1: Manualna metoda spektrometryczna
- Title (EN)
- Water quality — Determination of ammonium — Part 1: Manual spectrometric method
Step-by-step procedure
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Sampling and storage
Polyethylene or glass bottles; analysis as quickly as possible or storage at 2–5 °C. Acidification with sulfuric acid to pH < 2 may also be used for preservation, provided that absorption of ammonia from the air is avoided (clause 6).
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Test portion
At most 40 ml (ammonium nitrogen up to 1 mg/l); for higher concentrations a smaller test portion. Samples containing suspended matter are allowed to settle or filtered by gravity through a pre-rinsed glass fibre paper; alternatively they may be distilled. Transfer the test portion to a 50 ml flask and, if necessary, dilute to 40 ± 1 ml with ammonium-free water (7.1–7.2).
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Formation of the coloured compound
Add 4.00 ± 0.05 ml of colour reagent and mix, then 4.00 ± 0.05 ml of sodium dichloroisocyanurate solution and mix — the pH should be 12.6 ± 0.1. Dilute to the mark with water, shake and place the flask in the water bath at 25 ± 1 °C (7.3.1).
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Measurement
After at least 60 min remove the flask from the bath and measure the absorbance at the maximum (about 655 nm) in a cell of suitable path length against ammonium-free water in the reference cell (7.3.2).
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Blank test
In the same way, with 40 ± 1 ml of ammonium-free water instead of the test portion (7.4).
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Calibration
Into nine 50 ml flasks add from a burette 0–40 ml of the 1 mg/l standard solution (0–40 µg of nitrogen), dilute to 40 ± 1 ml and proceed as for the sample; 10 and 40 mm cells according to Table 1. The graph of absorbance (after subtracting the zero member) against the mass of nitrogen should be linear and pass through the origin (7.5).
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Calculation
A_r = A_s − A_b (in cells of the same path length); from the graph for the given path length read the mass of nitrogen m_N in µg; concentration ρ_N = m_N / V in mg/l, where V is the volume of the test portion in ml (clause 8). Conversions to NH₄⁺ and NH₃ — Table 2.
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Control
Each time the method is used, the absorbances of the blank and the calibration series are recorded to detect contamination with ammonium or a deficient reagent (11.2); when the method is first used, the total standard deviation is estimated (11.3).
Required equipment and apparatus
| Equipment | Example | Indicative price |
|---|---|---|
| Spectrometer | for operation at 655 nm, with cells of optical path length 10–50 mm (5.1) | — |
| Water bath or incubator | maintained at 25 ± 1 °C (5.2) | — |
| 50 ml one-mark volumetric flasks | for the test solutions and the calibration series (7.2, 7.5) | — |
| Burette | for adding the standard solution to the calibration series (7.5.1) | — |
| Laboratory glassware | cleaned with the cleaning solution (4.7) and rinsed thoroughly with ammonium-free water | — |
Reagents, media and consumables
| Reagent | CAS | Details |
|---|---|---|
| Ammonium-free water | — | distilled water passed through a strongly acidic cation exchange resin in the hydrogen form, or redistilled with 0.10 ml of sulfuric acid (1.84 g/ml) per 1000 ml, discarding the first 50 ml of distillate; stored with about 10 g of resin per litre (4.1) |
| Colour reagent | — | dissolve 130 ± 1 g of sodium salicylate and 130 ± 1 g of trisodium citrate dihydrate in water, make up to about 950 ml, add 0.970 ± 0.005 g of sodium nitroprusside dihydrate and dilute to 1000 ml; stable for at least 2 weeks in an amber glass bottle (4.2) |
| Sodium dichloroisocyanurate solution | — | 32.0 ± 0.1 g of sodium hydroxide in 500 ± 50 ml of water, after cooling 2.00 ± 0.02 g of sodium dichloroisocyanurate dihydrate; dilute to 1000 ml; stable for at least 2 weeks in an amber glass bottle (4.3) |
| Ammonium chloride — standard solutions | 12125-02-9 | 1000 mg/l of nitrogen: 3.819 ± 0.004 g of NH₄Cl dried at 105 °C for at least 2 h, diluted to 1000 ml — stable for at least 1 month; 100 mg/l — stable for 1 week; 1 mg/l — prepared immediately before use (4.4–4.6) |
| Glassware cleaning solution | — | 100 ± 2 g of potassium hydroxide in 100 ± 2 ml of water, after cooling 900 ± 50 ml of 95 % (V/V) ethanol; stored in a polyethylene bottle (4.7) |
Health and safety (OHS)
- The dichloroisocyanurate solution contains sodium hydroxide (32 g/l) and the glassware cleaning solution contains potassium hydroxide in ethanol; these and the other reagents are handled according to the safety data sheets
Frequently asked questions
Which standard describes this test?
The test is performed according to PN-ISO 7150-1:2002 (ISO 7150-1:1984) — “Water quality — Determination of ammonium — Part 1: Manual spectrometric method”.
How does this method work?
Spectrometric measurement at about 655 nm of the blue compound formed by the reaction of ammonium with salicylate and hypochlorite ions in the presence of sodium nitrosopentacyanoferrate(III) (sodium nitroprusside). Hypochlorite ions are generated in solution by the alkaline hydrolysis of sodium dichloroisocyanurate, and the reaction of the chloramine with salicylate takes place at pH 12.
What is the measuring range and accuracy?
Range: ammonium nitrogen up to 1 mg/l with a 40 ml test portion; higher concentrations in smaller test portions; Limit of detection: 0.003–0.008 mg/l (40 mm cell, 40 ml test portion); Wavelength: about 655 nm — the wavelength of maximum absorbance is checked when the method is first used; Colour development: at least 60 min in a water bath at 25 ± 1 °C; all determinations and calibrations at the same temperature (± 1 K).
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?
Spectrometer, Water bath or incubator, 50 ml one-mark volumetric flasks, Burette, Laboratory glassware.
Where is this test used?
Drinking water — ammonium 0.50 mg/l (Journal of Laws 2026, item 748, Annex 1 Part C); where chloramination is used, a group A monitoring parameter (Annex 3); Most raw waters (clause 1); Waste water — PN-ISO 7150-1 is one of the reference methods for ammonium nitrogen (Journal of Laws 2019, item 1311, Annex 12); Excessively coloured or saline waters — after distillation according to ISO 5664 (clause 10).
What safety precautions apply?
The dichloroisocyanurate solution contains sodium hydroxide (32 g/l) and the glassware cleaning solution contains potassium hydroxide in ethanol; these and the other reagents are handled according to the safety data sheets.
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 7150-1.