ISO 6058:1984

Overview

ISO 6058:1984 specifies a standardized EDTA titrimetric method for the determination of calcium content in water. This international standard outlines a precise procedure applicable to various water types including groundwater, surface water, and drinking water. It is also suitable for municipal and industrial raw waters, assuming no significant interference from heavy metals. Notably, this method is unsuitable for seawater or similar waters with high salt concentrations. The standard covers calcium concentrations ranging from 2 to 100 mg/L, with provisions for dilution of samples exceeding this range.

Developed by ISO Technical Committee ISO/TC 147 on water quality, ISO 6058 provides clear guidance for laboratory analysis to ensure consistent and reliable measurement of calcium levels critical for assessing water quality.

Key Topics

• Scope and Applicability Designed for calcium determination in freshwaters and potable water sources; unsuitable for seawater due to high salt interference. Applicable concentration range is 2 to 100 mg/L of calcium; higher concentrations require sample dilution.

• Principle of Method Calcium ions are titrated using a disodium salt of ethylenediaminetetraacetic acid (EDTA) solution at pH 12–13. The indicator-murexide (HSN)-forms a red complex with calcium and changes color to light blue at the titration endpoint. Magnesium and other potential interfering ions are either precipitated out or controlled by the pH adjustment.

• Reagents and Equipment Analytical grade reagents including sodium hydroxide solution, titrated EDTA solution (approx. 10 mmol/L), and the HSN indicator are used. Standard laboratory glassware such as 25 mL burettes (ISO/R 385 class A) and volumetric flasks are specified. Calibration with a reference calcium standard is required for accuracy.

• Sample Preparation and Analysis Samples are neutralized if acidified during collection, diluted if above concentration limits, and titrated immediately after addition of reagents. The endpoint is carefully observed by color change, with precise volumes recorded for concentration calculation.

• Interferences and Limitations Certain metal ions-aluminum, iron, lead, copper, zinc, cobalt, manganese, and others-may interfere by either forming complexes or causing turbidity at the endpoint. The method suggests additions like sodium cyanide or triethanolamine to mitigate some interferences, but for heavily contaminated waters, alternative instrumental methods such as atomic absorption spectroscopy (ISO 7980) are recommended.

Applications

• Water Quality Monitoring Essential for routine analysis in water treatment plants to monitor hardness and calcium levels that affect scaling and corrosion.

• Environmental Assessment Helps in evaluating calcium content in natural waters for ecological studies and environmental impact assessments.

• Industrial Water Management Used in industries to monitor raw water and process water for calcium content to prevent operational issues related to water hardness.

• Drinking Water Compliance Supports compliance testing with regulatory standards on calcium in potable water supplies, ensuring safe and palatable water.

Related Standards

• ISO 5667 Series – Guidelines for sampling water, relevant for collecting samples compliant with ISO 6058 procedures.
• ISO 7980 – Atomic absorption spectrometric methods for the determination of calcium, suggested for analysis where interference affects EDTA titration results.
• ISO/R 385 – Specification for the calibration and use of laboratory burettes.
• ISO 30511 – Laboratory glassware specifications, relevant for ensuring accuracy of volumetric equipment used in titrations.

Keywords: ISO 6058, water quality standard, calcium determination, EDTA titrimetric method, water analysis, calcium content, water hardness, water testing, water sampling, interference mitigation, analytical water testing.