Overview
EN ISO 7393-3:2000 (CEN adoption of ISO 7393-3:1990) defines an iodometric titration method for the determination of total chlorine in water. The method measures total chlorine (free + combined chlorine, e.g., chloramines) over the range 0.01 to 0.21 mmol/L (about 0.71–15 mg/L). Annex B describes a direct titration variant typically used for treated drinking water at concentrations above 7 µmol/L (≈0.5 mg/L). This standard is intended for routine laboratory analysis within water quality monitoring and treatment control.
Key topics and requirements
- Scope and limits: Applicable for total chlorine expressed as chlorine (Cl2) from 0.01–0.21 mmol/L; direct titration for higher concentrations (Annex B).
- Analytical principle: Oxidation of iodide to iodine by total chlorine in acid solution, reduction of released iodine by a known excess of sodium thiosulfate, and back-titration with potassium iodate (iodometric titration).
- Reagents and apparatus: Specifies analytical-grade reagents (potassium iodide, phosphoric acid, starch indicator), sodium thiosulfate and potassium iodate standard solutions (both 10 mmol/L examples in the text), and standard laboratory glassware (chlorine-demand free).
- Sampling: Advises immediate analysis after sampling and references sampling guidance in ISO 5667-1 and ISO 5667-2.
- Interferences: Method is valid only in the absence of other oxidizing agents - e.g., bromine/iodine species, bromamines/iodoamines, ozone, hydrogen peroxide, chlorite, chlorine dioxide, permanganate, nitrite, some metal ions (Fe(III), Cu(II), Mn(III)), etc.
- Quality and reporting: Includes calculation formulae (conversion to mg/L using molar mass 70.91 g/mol), repeatability data, and mandatory test-report items (reference to standard, sample ID, results, deviations from procedure).
Applications
- Routine water quality testing in drinking-water treatment plants and distribution systems.
- Environmental monitoring of surface waters and effluents where total chlorine must be quantified.
- Process control for water disinfection and verification of residual chlorine (free + combined).
- Laboratories performing regulatory compliance testing, QA/QC checks, and method validation.
Who should use this standard
- Municipal and industrial water laboratories
- Drinking-water utilities and treatment operators
- Environmental agencies and regulatory bodies
- Contract analytical laboratories and QA/QC teams involved in disinfection monitoring
Related standards
Keywords: water quality, EN ISO 7393-3:2000, iodometric titration, total chlorine determination, free chlorine, chloramines, drinking water testing, chlorine analysis, water analysis standards.
