🫧 Dissolved Oxygen in Water

Physicochemistry PN-EN ISO 5814

Overview

STATUS (as of 28.10.2026). PN-EN ISO 5814:2013-04 — English version, published 17.04.2013, implements EN ISO 5814:2012 [IDT] and ISO 5814:2012 [IDT]; it replaced PN-EN 25814:1999. There is no Polish language version in the PKN catalogue. The standard is current — no withdrawal note. ISO 5814:2012 is the third edition, which replaced ISO 5814:1990.

SCOPE (abstract of the standard). An electrochemical method for the determination of dissolved oxygen in water by means of an electrochemical cell isolated from the sample by a gas-permeable membrane. The result is reported as the oxygen concentration in mg/l, as percentage saturation or both. The method measures oxygen corresponding to 1 % to 100 % saturation; most instruments allow measurement above 100 % (supersaturation), and such values can be measured when the outgassing of oxygen during sample handling and measurement is prevented.

APPLICATION (abstract of the standard). Field measurements, continuous monitoring of dissolved oxygen and laboratory measurements. The method is preferred for highly coloured and turbid waters and for waters in which iron and iodine-fixing substances interfere with the iodometric Winkler method (ISO 5813). It is suitable for drinking water, natural waters, waste waters and saline waters; for saline waters, e.g. sea and estuarine waters, a correction for salinity is essential.

STRUCTURE OF THE STANDARD (table of contents). Principle, interferences, reagents, apparatus, sampling, measuring technique and precautions, calibration, determination, calculation of the result (concentration in mg/l and percentage saturation); Annex A (informative) — physicochemical data for oxygen in water, Annex B (informative) — performance data.

SOLUBILITY OF OXYGEN. The solubility of oxygen in water decreases with increasing temperature and salinity, and the degree of saturation is the oxygen content expressed as a percentage of its maximum solubility under the same conditions — therefore instruments compensate for the effect of temperature, and in saline waters the result is corrected for salinity.

WATER MONITORING — LEGAL REQUIREMENTS. Regulation of the Minister of Infrastructure of 13 July 2021 (Journal of Laws 2021, item 1576), Annex 8, indicators 3.2.1 (dissolved oxygen) and 3.2.5 (oxygen saturation): in the monitoring of surface water bodies and groundwater bodies, the reference methodology for the electrochemical method is the standard transposing ISO 5814 or a test procedure; the regulation also lists the titrimetric method (PN-EN 25813) and the optical method (ISO 17289). Another methodology may be used once its equivalence with the reference methodology has been demonstrated (explanatory note 1).

WHAT WE DO NOT GIVE HERE. We do not have the text of the standard beyond its scope and table of contents, so we do not state the construction of the probe (electrode materials, electrolyte, membrane), the calibration procedure, the flow conditions of the sample at the membrane, the oxygen solubility tables of Annex A, the formulas for percentage saturation or the performance data of Annex B. Optical (luminescence) sensors are not covered by this standard — its subject is the electrochemical cell.

Method principle

Oxygen dissolved in the sample passes through the gas-permeable membrane into the electrochemical cell of the probe. Under steady-state conditions the current or potential of the probe is correlated with the dissolved oxygen concentration; the instrument converts the signal into mg/l or percentage saturation.

The probe signal depends on temperature, so instruments have temperature compensation. The response of the probe is affected by salinity (in saline waters a correction is essential), and reactive gases permeating the membrane, e.g. chlorine and hydrogen sulfide, disrupt its operation.

Applications

• Field measurements and continuous monitoring of dissolved oxygen
• Laboratory measurements
• Highly coloured and turbid waters, and waters in which iron and iodine-fixing substances interfere with the Winkler method (ISO 5813)
• Drinking water, natural waters and waste waters
• Saline waters (sea, estuarine) — with the mandatory correction for salinity

Key parameters

Standard

Standard number

PN-EN ISO 5814:2013-04

Title (PL)

Jakość wody — Oznaczanie tlenu rozpuszczonego — Metoda z czujnikiem elektrochemicznym

Title (EN)

Water quality — Determination of dissolved oxygen — Electrochemical probe method

Step-by-step procedure

1. Sampling

   Sampling is described in 7.1 of the standard (we do not quote it). Dissolved oxygen is determined immediately — directly in the water body or right after sampling (EPA 360.1: analyse immediately).

2. Calibration

   According to 7.3 of the standard and the instrument manufacturer's instructions (we do not quote the text of the standard).

3. Measurement

   The probe is immersed in the sample transferred to a vessel without aerating it; the measuring technique and precautions are given in 7.2 of the standard.

4. Corrections

   Temperature compensation in the instrument; in saline waters a correction for salinity (abstract of the standard).

5. Result

   Dissolved oxygen concentration in mg/l or percentage saturation, or both (clause 8 of the standard).

Required equipment and apparatus

Reagents, media and consumables

Health and safety (OHS)

• In the available scope the standard gives no warnings; reagents are handled according to the safety data sheets, the probe according to the manufacturer's instructions

Frequently asked questions