Overview
EN ISO 11732:2005 - "Water quality - Determination of ammonium nitrogen - Method by flow analysis (CFA and FIA) and spectrometric detection" - is a CEN-endorsed ISO standard that specifies validated procedures for measuring ammonium nitrogen (N‑NH4) in waters. It covers ground, drinking, surface and waste waters, using either flow injection analysis (FIA) or continuous flow analysis (CFA) with spectrometric detection. The standard applies to undiluted samples in the mass concentration range 0.1 mg/l to 10 mg/l, with the range extendable by adjusting operating conditions.
Key topics and technical requirements
- Analytical principle: FIA (and CFA) injects sample into a carrier stream; ammonia is liberated under alkaline conditions, diffuses across a hydrophobic membrane into a recipient stream containing a pH indicator, and the resulting colour change is measured in a flow photometer.
- Performance & throughput: Flow analysis methods automate wet chemistry and are suitable for high sample throughput (up to ~100 samples per hour).
- Concentration range: Designed for 0.1–10 mg/l N in undiluted samples; dilution or operating-condition changes allow adaptation.
- Interferences and sample handling:
- Volatile amines (e.g., methylamine) diffuse through the membrane and can cause positive bias; distillation at pH ~5.8 can reduce interference.
- Strongly acidic or buffered samples may not reach pH 12 after alkaline addition - pH adjustment (to pH 3–5) may be required before analysis.
- High metal ion concentrations can precipitate as hydroxides; EDTA (e.g., 30 g/l in reaction solution R1) is recommended to complex metals.
- Samples with total salts > 10 g/l should be diluted; particulate matter requires appropriate sample preparation/filtration.
- Reagents & calibration: The standard lists reagent types (carrier, alkaline reaction solution R1 with EDTA and boric acid, mixed indicators, ammonia stock and standards) and advises use of analytical‑grade water and regular blank checks. Example detector settings include target absorbance 0.3–0.5 at 590 nm (10 mm path) for the recipient solution.
- Quality & reporting: Clauses cover calculation, precision data, and the required elements of a test report.
Applications and who uses it
- Water quality laboratories (drinking water, wastewater, environmental monitoring)
- Municipal utilities, environmental consultants, research labs and regulatory bodies
- Process control in water treatment and industrial effluent monitoring
EN ISO 11732:2005 is especially useful where high-throughput, reproducible ammonium determinations are required.
Related standards (normative references)
- ISO 3696 - Water for analytical laboratory use
- ISO 5667-1/2/3 - Water sampling guidance
- ISO 8466-1 - Calibration and evaluation of analytical methods
Keywords: EN ISO 11732:2005, ammonium nitrogen, water quality, flow injection analysis, continuous flow analysis, FIA, CFA, spectrometric detection, ammonium determination, water analysis standard.
