Overview
EN ISO 7980:2000 (ISO 7980:1986) specifies a validated atomic absorption spectrometric (AAS) method for the determination of dissolved calcium (Ca) and magnesium (Mg) in raw and drinking waters. The method is intended primarily for waters with up to 50 mg/L Ca and 5 mg/L Mg (for higher concentrations a smaller sample aliquot is taken). It covers sample collection, reagent preparation, instrument conditions, calibration, calculation and reporting.
Key topics and technical requirements
- Technique: Flame atomic absorption spectrometry (air/acetylene or nitrous oxide/acetylene) with hollow cathode lamps for Ca and Mg.
- Wavelengths: Ca measured at 422.7 nm; Mg measured at 285.2 nm.
- Calibration: Use a set of calibration solutions prepared from a Ca–Mg standard (example standard: 20 mg Ca + 2 mg Mg per L). Calibration graphs must be linear within the working ranges.
- Working ranges (optimum):
- Air/acetylene: Ca 3–50 mg/L, Mg 0.9–5 mg/L
- Nitrous oxide/acetylene: Ca 2–20 mg/L, Mg 0.2–2 mg/L
- Interference control:
- Add lanthanum chloride (20 g/L) for air/acetylene to minimize refractory interferences (phosphate, sulfate, Al, Si).
- Add caesium chloride (20 g/L) for nitrous oxide/acetylene to reduce ionization effects.
- Sample preparation:
- Collect in polyethylene or polypropylene bottles.
- Acidify as soon as possible with 8 mL concentrated HCl per litre to prevent CaCO3 precipitation.
- Typical test solution: 10 mL sample → 100 mL volumetric flask with reagents; filter if particulate matter remains.
- Reagents/standards: Stock Ca and Mg solutions at 1 000 mg/L are used to prepare calibration standards; lanthanum and cesium additives specified.
- Quality control: Blank tests, frequent calibration checks, and routine slope checks. Reported precision: single-lab SD ~0.3–0.6 mg/L at representative levels; interlaboratory CVs ~2.9–6.9% in study.
Applications and who uses it
- Routine analysis of drinking water, raw water, and waters used in industrial processes where Ca/Mg (hardness) monitoring is required.
- Used by: municipal and private water laboratories, environmental testing laboratories, water utilities, regulatory agencies, and researchers validating treatment performance or compliance.
- Practical benefits: reliable quantification of Ca and Mg for water quality compliance, hardness assessment, treatment optimization and process control.
Related standards
- Prepared by ISO/TC 147 (Water quality). EN ISO 7980:2000 is the CEN-adopted version of ISO 7980:1986 and should be used alongside the latest ISO guidance and laboratory quality-assurance documents for analytical methods.
