🔬 Nitrites in Water
In short
Spectrometric determination of nitrite in drinking water, raw waters and waste waters by molecular absorption spectrometry. The test is performed according to PN-EN 26777:1999; Range: nitrite nitrogen up to 0.25 mg/l with a 40 ml test portion; smaller test portions for higher concentrations. The procedure comprises 8 steps; it is used for: Drinking water — nitrite 0.50 mg/l, 0.10 mg/l after treatment, and the condition [nitrate]/50 + [nitrite]/3 ≤ 1 (Journal of Laws 2026, item 748, Annex 1 Part B); where chloramination is used, a group A monitoring parameter (Annex 3), Raw waters (clause 1), Waste water — PN-EN 26777 is the reference method for nitrite nitrogen (Journal of Laws 2019, item 1311, Annex 12).
At a glance
- Standard: PN-EN 26777:1999
- Category: Physicochemistry
- Procedure steps: 8
- Range: nitrite nitrogen up to 0.25 mg/l with a 40 ml test portion; smaller test portions for higher concentrations
- Limit of detection: 0.001–0.002 mg/l (40 mm cell, 40 ml test portion)
- Wavelength: about 540 nm — the wavelength of maximum absorbance is checked when the method is first used
Overview
STATUS (as of 28.10.2026). PN-EN 26777:1999 — Polish version, published 28.07.1999, implements EN 26777:1993 [IDT] and ISO 6777:1984 [IDT]; it replaced PN-C-04576-06:1973. The standard is current — no withdrawal note.
SCOPE (clauses 1–2). A molecular absorption spectrometric method for the determination of nitrite in drinking water, raw water and waste water. With the maximum test portion of 40 ml, nitrite nitrogen is determined up to 0.25 mg/l. The limit of detection with 40 mm cells and a 40 ml test portion is 0.001–0.002 mg/l; 0.062 mg/l then gives an absorbance of about 0.66, and in a 10 mm cell 0.25 mg/l gives about 0.67 (data from an interlaboratory trial in the United Kingdom).
INTERFERENCES (2.4, clause 9, annex). Of the substances tested, only chloramine, chlorine, thiosulfate, sodium polyphosphate and iron(III) interfere significantly. If the alkalinity of the sample is high, orthophosphoric acid solution is added before dilution to obtain pH 1.9 ± 0.1; the method tolerates a hydrogen carbonate alkalinity of at least 300 mg/l in a 40 ml test portion.
SAMPLES (clause 6). Glass bottles; analysis as soon as possible, within 24 h of collection. Storage at 2–5 °C may preserve many types of sample, but this should be verified.
STANDARD SOLUTIONS (clause 10). Nitrite standard solutions may become unstable — the concentration of the 100 mg/l solution is checked by titrating potassium permanganate solution c(1/5 KMnO₄) = 0.01 mol/l: 50 ml of permanganate should require 35.02 ± 0.40 ml of the standard solution.
DRINKING WATER AND WASTE WATER — LEGAL REQUIREMENTS. Regulation of the Minister of Health of 22 May 2026 (Journal of Laws 2026, item 748), Annex 1 Part B: nitrite 0.50 mg/l (as NO₂), [nitrate]/50 + [nitrite]/3 ≤ 1, and 0.10 mg/l after treatment; measurement uncertainty — 20 % 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-EN 26777 as the reference method (molecular absorption spectrophotometry) for nitrite nitrogen in waste water (Annex 12, item 8).
CONVERSION (Table 2). 1 mg/l of nitrogen corresponds to 3.29 mg/l of nitrite (NO₂).
WHAT WE DO NOT GIVE HERE. We do not reproduce the figures of the precision table (Table 3) or of the table of the effect of other substances (annex).
Method principle
Nitrite in the sample reacts with 4-aminobenzene sulfonamide in the presence of orthophosphoric acid at pH 1.9 to form a diazonium salt. With N-(1-naphthyl)-1,2-diaminoethane dihydrochloride — added together with the 4-aminobenzene sulfonamide in a single reagent — this salt forms a pink dye whose absorbance is measured at 540 nm.
Applications
- Drinking water — nitrite 0.50 mg/l, 0.10 mg/l after treatment, and the condition [nitrate]/50 + [nitrite]/3 ≤ 1 (Journal of Laws 2026, item 748, Annex 1 Part B); where chloramination is used, a group A monitoring parameter (Annex 3)
- Raw waters (clause 1)
- Waste water — PN-EN 26777 is the reference method for nitrite nitrogen (Journal of Laws 2019, item 1311, Annex 12)
- The precision data of the standard also include sewage effluent and sea water (Table 3)
Key parameters
| Parameter | Value |
|---|---|
| Range | nitrite nitrogen up to 0.25 mg/l with a 40 ml test portion; smaller test portions for higher concentrations |
| Limit of detection | 0.001–0.002 mg/l (40 mm cell, 40 ml test portion) |
| Wavelength | about 540 nm — the wavelength of maximum absorbance is checked when the method is first used |
| Reaction pH | 1.9 ± 0.1 |
| Measurement | at least 20 min after adding the reagent |
| Conversion | 1 mg/l N = 3.29 mg/l NO₂ |
Standard
- Standard number
- PN-EN 26777:1999
- Title (PL)
- Jakość wody — Oznaczanie azotynów — Metoda absorpcyjnej spektrometrii cząsteczkowej
- Title (EN)
- Water quality — Determination of nitrite — Molecular absorption spectrometric method
Step-by-step procedure
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Test portion
At most 40 ml (nitrite up to 0.25 mg/l of nitrogen); for higher concentrations a smaller test portion. Samples containing suspended matter are allowed to settle or filtered through a glass fibre paper (7.1).
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Reagent
Pipette the test portion into a 50 ml flask and dilute with water to 40 ± 2 ml — this is required to obtain the correct reaction pH. Add 1.0 ml of colour reagent, mix immediately, dilute to the mark and allow to stand; the pH should be 1.9 ± 0.1 (7.2, clause 9).
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Measurement
At least 20 min after adding the reagent, measure the absorbance at the maximum (about 540 nm) in a cell of suitable path length against water (7.2).
-
Colour correction
If the colour of the sample may interfere, a duplicate test portion is treated in the same way, but 1.0 ml of 1.5 mol/l orthophosphoric acid solution is added instead of the colour reagent (7.3).
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Blank test
40 ± 2 ml of water instead of the test portion (7.4).
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Calibration
Into nine 50 ml flasks add from a burette 0–10.00 ml of the 1.00 mg/l standard solution (0–10 µg of nitrogen), dilute to 40 ± 2 ml and proceed as for the sample; 10 and 40 mm cells according to Table 1 (50 mm cells may also be used). 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 (or A_s − A_b − A_c), all in cells of the same path length; from the graph the mass of nitrogen m_N in µg; ρ_N = m_N / V in mg/l. Result as ρ_N, ρ_NO₂ or c(NO₂⁻) — Table 2 (8.1).
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Checking the standard solution
50 ml of KMnO₄ solution c(1/5 KMnO₄) = 0.01 mol/l with 10 ± 1 ml of 2.5 mol/l sulfuric acid is titrated with the 100 mg/l standard solution (burette tip below the surface), warming to about 40 °C towards the end; the solution is suitable if the volume used lies within 35.02 ± 0.40 ml (clause 10).
Required equipment and apparatus
| Equipment | Example | Indicative price |
|---|---|---|
| Spectrometer | for measurements at 540 nm, with cells of optical path length 10–50 mm (clause 5) | — |
| Laboratory glassware | cleaned with approximately 2 mol/l hydrochloric acid and rinsed thoroughly with water (clause 5) | — |
| 50 ml one-mark volumetric flasks | for the test solutions and the calibration series (7.2, 7.5) | — |
| Burette | for the calibration series and for checking the standard solution (7.5, clause 10) | — |
| Glass bottles | for samples (clause 6); amber glass bottles for the colour reagent and standard solutions (clause 4) | — |
Reagents, media and consumables
| Reagent | CAS | Details |
|---|---|---|
| Orthophosphoric acid, 15 mol/l | 7664-38-2 | ρ = 1.70 g/ml (4.1) |
| Orthophosphoric acid, about 1.5 mol/l | — | 25 ml of the 15 mol/l acid into 150 ± 25 ml of water, after cooling dilute to 250 ml; stable for at least 6 months in an amber glass bottle; for the colour correction and for samples of high alkalinity (4.2) |
| Colour reagent | — | 40.0 ± 0.5 g of 4-aminobenzene sulfonamide in a mixture of 100 ± 1 ml of 15 mol/l orthophosphoric acid and 500 ± 50 ml of water; dissolve 2.00 ± 0.02 g of N-(1-naphthyl)-1,2-diaminoethane dihydrochloride in it and dilute to 1000 ml; stable for 1 month at 2–5 °C in an amber glass bottle (4.3) |
| Sodium nitrite — standard solution 100 mg/l of nitrogen | 7632-00-0 | 0.4922 ± 0.0002 g of NaNO₂ dried at 105 °C for at least 2 h, diluted to 1000 ml; stable for at least 1 month at 2–5 °C in an amber glass bottle; its concentration is checked with potassium permanganate (4.4, clause 10) |
| Sodium nitrite — standard solution 1.00 mg/l of nitrogen | — | 10 ml of the 100 mg/l solution diluted to 1000 ml; prepared each day as required and discarded after use (4.5) |
Health and safety (OHS)
- The colour reagent is hazardous — skin contact or ingestion of the reagent or its ingredients must be avoided (warning to 4.3)
- Handle the 15 mol/l orthophosphoric acid and the hydrochloric acid used for cleaning glassware according to the safety data sheets
Frequently asked questions
Which standard describes this test?
The test is performed according to PN-EN 26777:1999 — “Water quality — Determination of nitrite — Molecular absorption spectrometric method”.
How does this method work?
Nitrite in the sample reacts with 4-aminobenzene sulfonamide in the presence of orthophosphoric acid at pH 1.9 to form a diazonium salt.
What is the measuring range and accuracy?
Range: nitrite nitrogen up to 0.25 mg/l with a 40 ml test portion; smaller test portions for higher concentrations; Limit of detection: 0.001–0.002 mg/l (40 mm cell, 40 ml test portion); Wavelength: about 540 nm — the wavelength of maximum absorbance is checked when the method is first used; Reaction pH: 1.9 ± 0.1.
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, Laboratory glassware, 50 ml one-mark volumetric flasks, Burette, Glass bottles.
Where is this test used?
Drinking water — nitrite 0.50 mg/l, 0.10 mg/l after treatment, and the condition [nitrate]/50 + [nitrite]/3 ≤ 1 (Journal of Laws 2026, item 748, Annex 1 Part B); where chloramination is used, a group A monitoring parameter (Annex 3); Raw waters (clause 1); Waste water — PN-EN 26777 is the reference method for nitrite nitrogen (Journal of Laws 2019, item 1311, Annex 12); The precision data of the standard also include sewage effluent and sea water (Table 3).
What safety precautions apply?
The colour reagent is hazardous — skin contact or ingestion of the reagent or its ingredients must be avoided (warning to 4.3); Handle the 15 mol/l orthophosphoric acid and the hydrochloric acid used for cleaning glassware 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-EN 26777.