Overview - EN ISO 7393-1:2000 (Water quality, DPD titrimetric method)
EN ISO 7393-1:2000 specifies a titrimetric procedure for the determination of free chlorine and total chlorine in water using N,N‑diethyl‑1,4‑phenylenediamine (DPD). The method covers routine laboratory analysis for many fresh waters at concentrations from about 0.0004 to 0.07 mmol/l (≈0.03–5 mg/l Cl2); higher concentrations can be measured after dilution. Sea water and waters containing significant bromide or iodide require special procedures. The document is the CEN-adopted version of ISO 7393-1:1985.
Key topics and technical requirements
- Principle: DPD reacts with free chlorine to form a colored compound at pH ~6.2–6.5; titration with a standard ammonium iron(II) sulfate solution is used to reach a colourless end point. For total chlorine, potassium iodide is added prior to titration to liberate combined chlorine as iodine, which is then measured by the same titrimetric end point.
- Reagents and solutions: DPD reagent, pH buffer (pH 6.5), potassium iodide (KI), ammonium iron(II) sulfate titrant and standardization against potassium dichromate are specified. Storage and shelf-life guidance (e.g., protecting reagents from light) are included.
- Procedure: Two test portions per sample-one for free chlorine, one for total chlorine-with controlled addition order (buffer, DPD, sample; plus KI for total) and prompt titration.
- Interferences and corrections: Notes on oxidized manganese, bromine/iodine, bromamines, ozone and chlorine dioxide; procedures to correct or account for interferences (including use of arsenite/thioacetamide to assess Mn interference) are described.
- Accuracy & precision: Repeatability and reproducibility information and examples from interlaboratory evaluations are provided. Calculation formulas convert titrant volumes to chlorine concentration (mmol/l and conversion to mg/l).
Practical applications
- Routine monitoring of drinking water, distribution systems, wastewater effluent, and process waters where chlorine residuals are controlled.
- Compliance testing for regulatory programs and internal quality assurance in water treatment plants.
- Field/portable lab verification after appropriate sample handling (avoid light, heat and delays).
- Useful for operators assessing disinfection efficiency, residual decay and chlorination dosing.
Who would use this standard
- Environmental and municipal water laboratories
- Water utility operators and process control teams
- Environmental consultants and compliance auditors
- Manufacturers of reagents and titration kits for chlorine analysis
Related standards
- ISO 7393‑2 - DPD colorimetric method for routine control (complements Part 1)
- ISO 7393‑3 - Iodometric titration method for total chlorine (alternative for higher concentrations)
Keywords: EN ISO 7393-1:2000, water quality, free chlorine, total chlorine, DPD titrimetric method, chlorine determination, titration, potassium iodide, ammonium iron(II) sulfate.