Overview
EN 27888:1993 (ISO 7888:1985) - "Water quality - Determination of electrical conductivity" specifies a standardized method for measuring the electrical conductivity of all types of water. The method provides a practical indicator of the concentration of ionizable solutes and is used for monitoring surface waters, process waters in water supply and treatment plants, and waste waters. Results are expressed as electrical conductivity at a reference temperature (usually 25 °C) and reported in Siemens per metre (S/m) or derived units (for example mS/m, µS/cm).
Key topics and requirements
- Measurement principle: Direct determination of conductivity using electrode or induction-type conductivity cells; conductance multiplied by the cell constant yields conductivity.
- Cell constant: Must be known or determined using potassium chloride (KCl) standard solutions. Cell constant should be checked at least every six months.
- Calibration standards: KCl standard solutions are specified (examples in the standard: 0.1, 0.01, 0.001 mol·L⁻¹ with conductivities at 25 °C of ~1290, 141 and 14.7 mS/m respectively). Calibration must be carried out at the reference temperature.
- Temperature control and correction:
- Reference temperature: 25.0 °C (precision ±0.1 °C recommended; routine ±0.5 °C acceptable).
- Temperature coefficient (α) and correction factors are used to convert measurements made at other temperatures to the 25 °C reference.
- Instruments may include automatic temperature compensation-calibrate per manufacturer instructions.
- Electrode care: Platinum electrodes used for precision work should be platinized (platinizing solution specified) and maintained to avoid drying or fouling.
- Sampling and sample handling:
- Use polyethylene bottles, fill completely, seal tightly.
- Store in the dark at ~4 °C if delay is unavoidable; bring to 25 °C before measuring.
- No effective chemical preservative-measure as soon as practicable.
- Interferences: Atmospheric CO2/NH3 (especially in waters
