ISO 7393-2:2017 PDF

Overview

ISO 7393-2:2017 specifies a routine, field- and laboratory-applicable colorimetric method (DPD) for the determination of free chlorine and total chlorine in water. The method uses N,N-dialkyl-1,4-phenylenediamine (DPD) to form a red colour complex that is measured by photometer or by visual comparison to calibrated standards. It is designed primarily for drinking water and other low-pollution waters and covers practical concentration ranges (about 0.0004–0.07 mmol/L, approx. 0.03–5 mg/L Cl2). Special procedures are required for seawater and waters with significant bromides/iodides.

Key topics and requirements

• Principle: Direct DPD reaction for free chlorine; DPD + excess potassium iodide for total chlorine.
• Measurement: Photometric absorbance or visual comparator against regularly calibrated standards.
• Reagents and buffering: Ready-to-use reagents (liquids, powders, tablets) must contain essential reagents and a buffer system to achieve a measurement pH typically 6.2–6.5. Sample pH should be within 4–8; adjust with sodium hydroxide or sulfuric acid if necessary.
• Interferences: Guidance on common interferences (bromine, iodine, chlorine dioxide, ozone, hydrogen peroxide, oxidized manganese, Cu(II), Fe(III), coloured/turbid samples). Some interferences are suppressed by disodium EDTA in reagents; oxidized manganese can be quantified using arsenite or thioacetamide treatment.
• Sampling and calibration: Applicable to both laboratory and field testing with mobile photometers; calibration and measurement procedures are specified (including dilution for higher concentrations).
• Annexes:
  • Annex A - differentiation of combined chlorine species (monochloramine, dichloramine, nitrogen trichloride).
  • Annex C - procedure for disposable planar reagent-filled cuvettes using a mesofluidic channel pump / colorimeter.

Applications and users

ISO 7393-2:2017 is intended for routine control and monitoring where reliable chlorine measurement is required:

• Drinking water utilities and treatment plant operators
• Field technicians using portable photometers and comparator kits
• Laboratories performing regulatory compliance or routine quality control
• Pool and spa operators, cooling-water monitoring, and environmental monitoring teams (with caution for complex matrices) The standard supports rapid on-site decisions and laboratory confirmation of residual disinfectant levels.

Related standards

• ISO 3696 - Water for analytical laboratory use
• ISO 5667-3 - Sampling: preservation and handling of water samples
• ISO 8466-1 - Calibration and evaluation of analytical methods (statistical treatment)

Keywords: ISO 7393-2, DPD colorimetric method, free chlorine, total chlorine, water quality, photometer, field testing, drinking water, chloramines, routine control.