Overview
ISO 10359-1:1992 specifies an electrochemical probe method for the determination of dissolved fluoride in potable and lightly polluted waters. The technique uses a fluoride ion‑selective electrode (F‑ISE) and a reference electrode to measure the potential difference proportional to fluoride ion concentration. The method is directly suitable for fluoride concentrations from 0.2 mg/L to 2 000 mg/L (2.0 g/L) and, after concentration enhancement, can detect levels down to about 0.02 mg/L.
Key topics and requirements
- Principle: Potential difference between F‑ISE and reference electrode follows the Nernst relationship; measurements refer to fluoride ion concentration under defined assumptions.
- Measurement range & sensitivity: 0.2 mg/L–2 000 mg/L directly; lower limits achievable by spiking/concentration procedures.
- pH control and interferences:
- Buffer samples to pH 5–7 (recommended pH ~5.2) to avoid HF formation and hydroxide interference.
- Use a Total Ionic Strength Adjustment Buffer (TISAB) containing CDTA to decomplex Ca2+, Mg2+, Al3+, Fe3+; note boron‑fluoride complexes (BF4−) are not decomplexed by this buffer.
- Instrumentation & reagents:
- High‑impedance millivolt meter (≥10^12 Ω) resolving 0.1 mV.
- Fluoride ion‑selective electrode with slope ≥55 mV per decade at 25 °C and a calomel or Ag/AgCl reference electrode.
- Thermostatted measuring cell (25 °C ±0.2 °C), magnetic stirrer, membrane filtration (0.45 μm) optional.
- Standard solutions (stock 1000 mg/L NaF and working standards, e.g. 10, 5, 1, 0.5, 0.2 mg/L) and TISAB prepared as specified.
- Calibration & procedure: Establish a five‑point calibration (semi‑log graph or Nernst equation), condition and recondition electrodes to avoid memory effects, maintain consistent ionic strength and temperature.
- Sampling & handling: Collect in fluoride‑free polyethylene bottles, analyze preferably within 3 days; no preservative normally required.
Applications
- Routine monitoring of drinking water and surface water fluoride levels.
- Compliance testing for water quality programs and regulatory reporting.
- Environmental laboratory analysis, public utilities, and research where electrochemical fluoride measurement is appropriate.
- Rapid field or laboratory screening for fluoride in potable and lightly polluted waters.
Who should use this standard
- Environmental and municipal water laboratories
- Public health and regulatory agencies
- Water quality consultants and treatment plant operators
- Analytical chemists working with ion‑selective electrodes
Related standards
- ISO 10359-2 - Determination of total inorganically bound fluoride (decomposition/distillation + potentiometry)
- ISO 5667-3 - Water quality - Sampling - Guidance on preservation and handling of samples
Keywords: ISO 10359-1:1992, fluoride determination, water quality, fluoride ion‑selective electrode, electrochemical probe method, TISAB, potable water testing.