ISO 10359-2:1994

Overview

ISO 10359-2:1994 - "Water quality - Determination of fluoride - Part 2" defines a laboratory procedure for the determination of inorganically bound total fluoride in water after chemical digestion and steam distillation. The method is intended primarily for industrial and waste waters that are highly inorganic‑contaminated, with fluoride ion concentrations above 0.2 mg/L. The standard describes sample preparation, digestion (alkaline evaporation and fusion), steam distillation (phosphoric/sulfuric acid), and potentiometric measurement using a fluoride ion‑selective electrode.

Key topics and technical requirements

• Scope & applicability: For inorganically bound total fluoride in heavily contaminated wastewaters (>0.2 mg/L).
• Interferences: Recognizes complexation and precipitation with cations (Ca2+, Mg2+, Al3+, Fe3+) and boron-fluoride complexes; uses digestion and distillation to eliminate these interferences.
• Sample preparation: Evaporation to dryness in alkaline medium, fusion of residue with sodium hydroxide, dissolution prior to distillation.
• Distillation: Steam distillation in presence of phosphoric and sulfuric acids; recommended distillate volume and distillation rate control.
• Measurement: Potentiometric determination with a fluoride ion‑selective electrode calibrated with a series of standard solutions and measured in a TISAB (total ionic strength adjustment buffer) at controlled temperature (≈25 °C).
• Reagents & apparatus: Specifies analytical‑grade reagents (HCl, H3PO4, H2SO4, NaOH, TISAB components), nickel dishes/crucibles, borosilicate distillation glassware, heating jacket, magnetic stirrer and a millivoltmeter/ion‑selective electrode system.
• Quality control: Daily calibration checks, electrode conditioning, blank determinations, and periodic calibration after digestion/distillation; electrode slope should be ≥55 mV per decade change in fluoride concentration.
• Precision: Interlaboratory trials were conducted (reported in the standard) to establish repeatability and reproducibility.

Applications

• Regulatory and compliance testing of industrial effluents and concentrated wastewaters for total fluoride content.
• Environmental monitoring where fluoride is bound in inorganic complexes not measurable by direct electrode methods.
• Treatment plant influent/effluent characterization and forensic analyses of contaminated sites.

Who should use this standard

• Environmental and analytical laboratories performing fluoride analysis on industrial/waste waters.
• Water quality managers, regulatory authorities, and consultants assessing fluoride loads or compliance.
• Research labs studying fluoride speciation in complex inorganic matrices.

Related standards

• ISO 10359-1 - Electrochemical probe method for potable and lightly polluted water (direct measurement).
• ISO 5667-3 - Guidance on sampling, preservation and handling of water samples.

Keywords: ISO 10359-2:1994, water quality, fluoride determination, inorganically bound total fluoride, steam distillation, ion‑selective electrode, TISAB, waste water analysis.