ISO 5814:2012

Overview

ISO 5814:2012 - "Water quality - Determination of dissolved oxygen - Electrochemical probe method" - specifies an electrochemical probe procedure for measuring dissolved oxygen (DO) in water. The method uses an electrochemical cell separated from the sample by a gas‑permeable membrane and reports DO as mg/L and/or % saturation. It covers field, continuous and laboratory measurements, is preferred for highly coloured or turbid waters, and is recommended when iodometric (Winkler) titration (ISO 5813) is unsuitable (e.g., iron‑ or iodine‑fixing substances).

Key topics and technical requirements

• Principle: probe with electrolyte and at least two electrodes (galvanic or polarographic) detects oxygen diffusing through a selective membrane; signal is temperature‑ and pressure‑dependent and proportional to oxygen partial pressure.
• Measurement range: designed for 1% to 100% saturation; many instruments can read above 100% (supersaturation). Special handling is required to avoid outgassing when measuring >100%.
• Calibration and checks:
  • Zero check: deoxygenate water (e.g., ~1 g sodium sulfite + ~1 mg cobalt(II) salt per 1 L) or use nitrogen atmosphere.
  • Calibration at saturation: ISO 5814:2012 specifies calibration using water‑vapour‑saturated air (new vs earlier editions).
  • Daily checks recommended and after ambient changes (temperature/pressure).
• Sampling and handling: minimize oxygen exchange and turbulence; prefer in‑situ measurement or gas‑tight flow‑through systems; use laminar filling and water‑displacing pumps only.
• Interferences and maintenance: gases (chlorine, H2S, ammonia, halogens) and substances that foul membranes (oils, solvents, biofilms, sulfides, carbonates) can bias readings; follow manufacturer guidance for membrane/electrolyte replacement.
• Reporting: express DO to one decimal place (mg/L) or nearest whole % for saturation; record water temperature, atmospheric pressure and salinity if used.

Applications and users

ISO 5814 is used by:

• Environmental monitoring laboratories and field teams measuring rivers, lakes, estuaries and coastal waters
• Wastewater treatment operators and compliance testing programs
• Drinking‑water quality professionals and utilities
• Aquaculture and ecological research where DO dynamics, supersaturation or turbid/highly coloured waters are a concern
• Continuous monitoring system integrators and manufacturers of DO probes/meters

Practical benefits include rapid in‑situ readings, suitability for coloured/turbid samples, and compatibility with continuous monitoring systems.

Related standards

• ISO 5813 - Winkler titration method for dissolved oxygen (used for comparison/validation where applicable)
• ISO 3696 - Water for analytical laboratory use (reagent water quality referenced in ISO 5814)

Keywords: ISO 5814, dissolved oxygen, electrochemical probe, water quality, DO measurement, calibration, membrane probe, polarographic, galvanic, supersaturation, sampling, ISO 5813.