Overview
EN 26777:1993 (identical with ISO 6777:1984) defines a molecular absorption spectrometric method for the determination of nitrite in potable, raw and waste water. The method is based on forming a pink azo dye by reaction of nitrite with 4‑aminobenzenesulfonamide and N-(1‑naphthyl)-1,2-diaminoethane dihydrochloride in orthophosphoric acid (pH ≈ 1.9) and measuring absorbance around 540 nm. The standard includes reagent formulations, sample handling, calibration, limits of detection and a full annex on interferences.
Key topics and technical requirements
- Scope and field of application: Suitable for potable, raw and sewage/waste water; maximum test portion 40 ml (typical range up to 0.25 mg N/L nitrite when using 40 ml).
- Chemical principle: Diazonium coupling reaction producing a pink-coloured dye; spectrophotometric measurement at ~540 nm.
- Reagents and preparation: Orthophosphoric acid solutions, a hazardous colour reagent (4‑aminobenzenesulfonamide + N‑(1‑naphthyl) reagent), and standard nitrite solutions. Stability notes: some standard nitrite solutions may become unstable and must be checked.
- Calibration and measurement: Prepare a calibration graph from prepared standard solutions; use cells of 10–50 mm optical path length (10 mm and 40 mm commonly used). Blank and colour-correction procedures are specified.
- Performance characteristics:
- Limit of detection (40 mm cell, 40 ml test portion): ~0.001–0.002 mg N/L.
- Typical sensitivity: e.g., with 40 ml test portion and 40 mm cell, ~0.062 mg/L gives an absorbance ≈ 0.66.
- Precision data (repeatability/reproducibility) reported from an interlaboratory trial.
- Interferences: Annex lists effects of common substances. Significant interferences include chlorine, chloramine, thiosulfate, sodium polyphosphate (hexametaphosphate) and iron(III); alkalinity may require pH adjustment using orthophosphoric acid.
- Quality control: Procedure for checking standard nitrite solution concentration using titration against a potassium permanganate standard is provided.
Applications and users
This standard is intended for:
- Water and wastewater testing laboratories
- Drinking water utilities and regulatory compliance monitoring
- Environmental monitoring and pollution control agencies
- Wastewater treatment operators and process control labs
- Environmental consultants and contract analytical laboratories
Use cases include routine monitoring of nitrite concentrations in drinking water, process control in treatment plants, effluent compliance testing, and research where accurate low-level nitrite measurement is required.
Related standards
- ISO 6777:1984 - the original international standard identical to EN 26777:1993 (method and scope are the same).
- National or regional water quality regulations may reference EN 26777/ISO 6777 for nitrite analysis.
Keywords: nitrite determination, water quality, spectrometric method, EN 26777, ISO 6777, nitrite analysis, spectrophotometry, water testing, interferences, detection limit.
