Overview
ISO 7150-1:1984 specifies a manual spectrometric method for the determination of ammonium (ammonium nitrogen) in water. The method measures a blue compound formed by reaction of ammonium with sodium salicylate, sodium dichloroisocyanurate (generating hypochlorite in situ) and sodium nitroprusside, with spectrometric measurement at about 655 nm. It applies to potable water and most raw and waste waters; excessively coloured or saline samples should be pre‑treated by distillation (see ISO 5664).
Key topics and technical requirements
- Analytical range and sensitivity
- Maximum test portion: 40 ml; with this volume ammonium‑N up to 1 mg/L can be determined. Higher concentrations are handled by using smaller test portions.
- Limit of detection (40 mm cell, 40 ml): ≈ 0.003–0.008 mg/L (ammonium nitrogen).
- Example sensitivities: 40 ml + 40 mm cell, 0.200 mg/L gives absorbance ≈ 0.69; 40 ml + 10 mm cell, 0.750 mg/L gives absorbance ≈ 0.65.
- Reaction conditions
- Reaction pH ≈ 12.6 (alkaline); incubation in a water bath or incubator at 25 ± 1 °C.
- Incubation time: measure after at least 60 minutes.
- Instrumentation and reagents
- Spectrometer at ~655 nm, cells path length 10–50 mm.
- Key reagents: sodium salicylate + trisodium citrate, sodium nitroprusside, sodium dichloroisocyanurate solution.
- Reagent and standard stability notes included (e.g., colour reagent stable ~2 weeks).
- Quality control and calibration
- Nine‑point calibration series; blank tests and recording of actual absorbance values every batch.
- Routine use of a control standard (≈50% of highest calibration concentration) to detect bias.
- Interferences
- Primary amines (e.g., aniline, ethanolamine) and substances that reduce hypochlorite can cause serious interference.
- In saline waters, magnesium precipitation can interfere; distillation is recommended when citrate complexing capacity is exceeded.
Practical applications and users
ISO 7150-1 is used by:
- Environmental and water testing laboratories
- Drinking water and wastewater utilities
- Regulatory agencies and compliance monitoring programs
- Research labs conducting water quality analysis
Typical uses include routine monitoring of ammonium in potable water, raw and treated wastewaters, process control in treatment plants, and environmental compliance testing where a validated spectrophotometric ammonium method is required.
Related standards
- ISO 5664 - Distillation procedure for ammonium prior to analysis (referenced for coloured/saline samples)
- ISO 7150-2 - Automated spectrometric method (covers automation of the chemistry described here)
Keywords: ISO 7150-1, ammonium determination, manual spectrometric method, water quality, ammonium nitrogen, spectrophotometric analysis, water testing, potable water, wastewater.
