Overview
ISO 7888:1985, titled Water Quality - Determination of Electrical Conductivity, is an international standard developed by the International Organization for Standardization (ISO). This standard specifies a precise method for measuring the electrical conductivity of all types of water. It serves as a critical tool for monitoring water quality in various contexts including surface waters, water supply distribution, treatment plants, and wastewater.
Electrical conductivity measurement, as defined in ISO 7888, reflects the ability of water to conduct an electric current, which is influenced primarily by the concentration and nature of dissolved ions. The standard also provides guidance on managing temperature compensation and interferences that may affect measurement accuracy.
Key Topics
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Scope and Application: The standard applies to all types of water-surface, process, and wastewater-to assess ion concentration and overall water quality.
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Measurement Principles:
- Electrical conductivity is the inverse of resistance and indicates ionic solute concentration.
- Conductivity is measured using specialized instruments equipped with conductivity cells.
- The cell constant, based on electrode geometry, must be carefully determined for precise readings.
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Temperature Compensation:
- Conductivity varies with temperature; therefore, measurements must be corrected to a reference temperature of 25°C for comparability.
- The standard describes mathematical correction formulas and factors to adjust conductivity values from actual measurement temperatures to the reference temperature.
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Calibration and Standards:
- Calibration uses potassium chloride (KCl) standard solutions of known conductivity.
- The document recommends specific cell constants based on the expected conductivity range to optimize measurement sensitivity.
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Equipment Requirements:
- Instruments include flow-through or immersion cells with multiple electrodes or induction electrodes.
- Electrode maintenance, including platinization, is highlighted to ensure accuracy.
- Temperature measuring devices must be precise to at least ±0.1°C for reliable correction.
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Sampling Procedures:
- Samples should be collected in polyethylene bottles, avoiding glass to reduce contamination.
- Prompt measurement is recommended to avoid changes caused by biological activity or gas exchange.
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Interferences and Limitations:
- Contaminants such as suspended solids, oils, or air bubbles on electrodes can impact results.
- The presence of gases like carbon dioxide or ammonia can influence conductivity, especially at low values (
