Overview
ISO 760:1978 - Determination of water (Karl Fischer method, general method) specifies a validated, general procedure for measuring water content (free water and water of crystallization) in most solid and liquid chemical products using the Karl Fischer titration. Two end‑point detection methods are defined: a visual titration (for colourless solutions and where no electrometric apparatus is available) and an electrometric titration (direct or back‑titration). The electrometric method is more accurate and is recommended for routine use.
Key topics and requirements
- Principle: water reacts quantitatively with iodine and sulfur dioxide in a pyridine/methanol (or 2‑methoxyethanol) solvent mixture (Karl Fischer reagent); reagent must be standardized against an exactly known mass of water.
- Two titration modes:
- Visual titration: endpoint by colour change; limited to colourless solutions.
- Electrometric titration: endpoint detected electrically (depolarization of the cathode causes a sudden current change); supports direct titration or back‑titration and gives higher accuracy.
- Reagent preparation and handling: reagent comprises iodine + SO2 dissolved in methanol/pyridine (2‑methoxyethanol may be used for better stability with carbonyl compounds). The standard gives instructions for reagent preparation, cooling during exothermic dissolution, and storage in dry, dark containers.
- Standardization and performance:
- Karl Fischer reagent water equivalent typically 3.5–4.5 mg/mL and must be standardized (daily if methanol solvent is used).
- Apparatus requirements include automatic burettes, titration vessels with “vaccine cap”, platinum electrodes (for electrometric titration), and controlled stirring.
- Precautions: drying of reagents and glassware, use of desiccants, and minimizing atmospheric moisture ingress are specified to maintain accuracy.
Applications
- Routine water content analysis in chemical manufacturing, pharmaceuticals, petrochemicals, polymers, cosmetics, food, and laboratory quality control.
- Determining free water and water of crystallization in solids and liquids where accurate moisture data is required for compliance, stability studies, or process control.
- Useful for laboratories that need an internationally recognized, reproducible Karl Fischer titration method.
Who should use this standard
- Analytical chemists and QC laboratories performing moisture analysis.
- Instrument and reagent manufacturers designing Karl Fischer titration systems.
- Regulatory and standards professionals specifying accepted test methods.
Related standards
- ISO 760 provides the general Karl Fischer method; product‑ or industry‑specific ISO/EN standards often reference or adapt this method with special precautions or sample preparation steps. Consult current ISO catalogs for updated or related methods.
Keywords: ISO 760, Karl Fischer, water determination, Karl Fischer titration, electrometric titration, visual titration, Karl Fischer reagent, water content analysis.