Overview
ISO 11732:2005 - "Water quality - Determination of ammonium nitrogen - Method by flow analysis (CFA and FIA) and spectrometric detection" - specifies validated procedures for measuring ammonium nitrogen in waters (ground, drinking, surface, waste). The standard covers both flow injection analysis (FIA) and continuous flow analysis (CFA) with spectrometric detection, for mass concentrations typically in the range 0.1 mg/L to 10 mg/L (as N). Flow methods automate wet-chemical reactions to support high-throughput laboratories (up to ~100 samples/hour).
Key topics and technical requirements
- Methods covered: FIA (Clause 3) and CFA (Clause 4) with photometric detection of an ammonia-induced pH indicator change after diffusion through a hydrophobic membrane.
- Analytical principle: sample alkalinized → ammonia diffuses across a PTFE membrane into an indicator-containing recipient stream → colour change measured at ~590 nm (wavelength range 580–600 nm) in a flow photometer.
- Working ranges & injection volumes:
- Working range I: 1–10 mg/L (example injection ~40 µL).
- Working range II: 0.1–1.0 mg/L (example injection ~360–400 µL).
- Reagents & solutions: carrier, alkaline reaction solution (R1 includes NaOH, boric acid and EDTA for metal complexing), indicator solution, ammonia recipient (R2), and calibrated ammonium standards (stock 1000 mg/L and diluted standards).
- Apparatus: low-pulsation pumps, diffusion cell with hydrophobic membrane (PTFE; e.g. 150–200 µm thickness, 0.5–2.0 µm pores), flow cell path lengths 10–50 mm, recording unit, optional autosampler.
- Interferences & mitigation:
- Volatile amines (methylamine, ethylamine) can cause positive bias - remove by distillation at pH ~5.8 if needed.
- Strongly acidic/buffered samples may not reach pH 12 - adjust sample pH to 3–5 before analysis.
- High metal ion concentrations can precipitate as hydroxides; add EDTA (example: 30 g/L in R1 for metals up to ~0.2 mg/L each).
- High total salt (>10 g/L) requires dilution; particulate-laden samples may need filtration.
- Quality: calibration requires multiple standards (≥5), blank checks, baseline stabilization, and precision evaluation (see Annex B).
Applications
- Routine monitoring of water quality, drinking water compliance, surface and groundwater assessment, and wastewater process control.
- Suitable for environmental laboratories, municipal water utilities, wastewater treatment operators, contract testing labs and research facilities requiring automated, high-throughput ammonium nitrogen analysis.
Related standards
Keywords: ISO 11732:2005, ammonium nitrogen, water quality, flow injection analysis (FIA), continuous flow analysis (CFA), spectrometric detection, diffusion cell, PTFE membrane, indicator, calibration.