Overview
EN ISO 13395:1996 (ISO 13395:1996) specifies automated wet-chemistry procedures for the determination of nitrite nitrogen (NO2–N), nitrate nitrogen (NO3–N) and their sum in waters using flow analysis (both Continuous Flow Analysis - CFA - and Flow Injection Analysis - FIA) with spectrometric detection. The method is designed for large sample series and high analysis frequency (up to ~100 samples per hour) and includes automatic sample dosing and online reagent mixing.
Key topics and technical requirements
- Method principle: Nitrate is reduced to nitrite (metallic cadmium reductor), then nitrite undergoes diazotization (sulfanilamide in acid) and coupling with N-(1‑naphthyl)ethylenediamine to form a coloured azo dye measured photometrically (flow detector). Nitrite alone is determined by omitting the cadmium reduction step.
- Flow modes: Differentiates FIA (sample injected into a continuous carrier stream) and CFA (sample continuously mixed with carrier).
- Reagents and buffers: phosphoric acid (or HCl alternative), sulfanilamide, N-(1‑naphthyl)ethylenediamine, imidazole or ammonium-based buffers, copper sulfate, surfactant, and cadmium granulate.
- Performance and limits: Working ranges provided in the standard - for nitrite(N) typical ranges are 0.01–0.1 mg/L (range II) and 0.1–1.0 mg/L (range I); for nitrite/nitrate(N) 0.2–2 mg/L (range II) and 2–20 mg/L (range I).
- Instrumental requirements: low-pulsation pumps, injector/autosampler, photometric flow cell (wavelength 520–560 nm), tubing/reactor coils, optional dialysis cell, and a cadmium reductor (minimum 90% reduction efficiency).
- Quality controls: calibration with at least five standards per working range, freshly prepared calibration solutions, degassing of carrier/reagent solutions, blank checks, and absorbance checks (e.g., a low-range standard should yield ≥0.04 absorbance per 10 mm path length).
- Safety/environment: handling and disposal of cadmium-containing waste and use of oxygen-free gas for the cadmium reductor where specified.
Applications and users
- Routine water quality testing for ground, surface, drinking and waste waters.
- Environmental monitoring laboratories, municipal drinking-water utilities, wastewater treatment facilities, and contract analytical labs requiring high-throughput nitrite/nitrate analysis.
- Manufacturers and integrators of flow-analysis instrumentation and automated analyzers implementing FIA/CFA spectrometric detection.
Related standards
- ISO 5667 series (water sampling guidance)
- ISO 3696 (water for analytical laboratory use)
- ISO 6777 (manual nitrite determination) - referenced for comparable chemistry
Keywords: EN ISO 13395, ISO 13395:1996, flow injection analysis, continuous flow analysis, nitrite nitrate determination, water quality testing, spectrometric detection.
