Overview
ISO 3699:1976 specifies a reference method for the determination of water content in anhydrous hydrogen fluoride (AHF) for industrial use using the Karl Fischer (KF) titration technique. The method applies to products with water contents between 0.01 % (m/m) and 0.5 % (m/m) and is intended as a reference procedure (ISO 3700 describes an alternative conductimetric routine method).
Key elements of the method:
- Addition of a cooled test portion of AHF to cooled, dry pyridine solvent containing 5 % anhydrous hydrogen fluoride.
- Subsequent electrometric KF titration of water with Karl Fischer reagent (water equivalent typically 4–6 mg/ml).
- Specialized apparatus and strict sample-cooling and handling procedures to control reactivity.
Key topics and technical requirements
- Scope: Accurate for 0.01–0.5 % (m/m) water in anhydrous hydrogen fluoride.
- Safety: Strong warnings - AHF is highly corrosive, volatile (bp ~19.5 °C), and toxic. Work only in well‑ventilated fume cupboards with appropriate PPE (rubber gloves, boots, gown, full head/face protection). In case of exposure, flush with water and seek immediate medical attention.
- Reagents and solvents: Dry pyridine solvent precooled (to ≈ −50 °C using dry ice/methanol) and prepared with ~5 % AHF; Karl Fischer reagent standardized per ISO/R 760.
- Apparatus: Cooling coil (stainless steel), measuring vessel with PTFE/glass/PTFE windows (marked at ≈40 ml), PTFE titration bottle (700–1 000 ml) with electrodes and inlet/outlet valves, overflow bottle, air dryer, magnetic stirrer and detection equipment per ISO/R 760.
- Procedure summary: Pre-titrate solvent, cool titration assembly, transfer ~40 ml test portion below solvent surface, add additional sample at controlled rate, allow mixture to warm to ambient, carry out electrometric titration, and calculate water content from volumes of KF reagent used, reagent water equivalent and sample masses/density.
- Result expression: Percent by mass calculated using titrant volumes, Karl Fischer reagent water equivalent, and measured sample mass; full calculation details are in the standard.
Applications and users
This ISO standard is intended for:
- Analytical chemistry laboratories in fluorochemical manufacturing and processing
- Quality control and product specification testing for anhydrous hydrogen fluoride
- Regulatory and safety compliance testing where accurate trace moisture measurement in AHF is required
- Research labs conducting material compatibility or process control involving HF
Keywords: ISO 3699:1976, anhydrous hydrogen fluoride, Karl Fischer titration, water content determination, KF titration, pyridine solvent, AHF safety, moisture analysis.
Related standards
- ISO 3137 - AHF sampling
- ISO 3138 - Non‑volatile acid content (titrimetric)
- ISO 3700 - Water content (conductimetric method, routine)
- ISO 3701 / ISO 3702 - Related compositional tests for industrial HF
- ISO/R 760 - General Karl Fischer titration guidance
For implementation, consult the full ISO 3699:1976 document for complete procedural details, safety instructions, figures of apparatus and exact calculation formulae.
Open preview (PDF)Anhydrous hydrogen fluoride for industrial use — Determination of water content — Karl Fischer method
