Overview
ISO 10336:1997 specifies a potentiometric Karl Fischer titration method for the direct determination of water in crude petroleum. The method covers water-content measurement in the range 0.05 % (m/m) to 2.00 % (m/m) for crude oils that contain between 0.005 % and 0.05 % (m/m) of mercaptan or sulfide-ion sulfur, and 0.02 % (m/m) to 2.00 % (m/m) when sulfur is below 0.005 % (m/m). The procedure uses a potentiometric end point in a volumetric Karl Fischer titrator after careful sample homogenization and precise sample weighing.
Key topics and requirements
- Analytical principle: Direct potentiometric Karl Fischer titration of a weighed test portion injected into a mixed titration solvent; end point detected by electrode potential.
- Reagents and solvents: Support for both pyridine-containing and pyridine-free Karl Fischer reagents, plus specified titration solvents (methanol, xylene, N‑ethyl piperidine or pyridine‑free solvent systems).
- Standardization: Daily standardization of the Karl Fischer reagent using known water additions; calculation of reagent water equivalence (F) and use of the formula w = (F × T) / (10 × m) to compute water content (m/m).
- Sampling & sample prep: Requires representative laboratory samples obtained per ISO 3170/3171 and immediate homogenization using a non‑aerating mixer; Annex A details sample handling and homogenization validation.
- Apparatus and consumables: Potentiometric Karl Fischer titrator, non‑aerating mixer, syringes/needles for injection and a balance accurate to ±0.1 mg.
- Precision and reporting: The standard gives repeatability and reproducibility limits (clause 10) and specifies reporting to the nearest 0.01 % (m/m). Test reports must include mixing conditions, sample temperatures, any deviations and reagent details.
- Safety: Notes potential hazards (e.g., chloroform, reagents) and requires appropriate lab safety practices.
Applications and users
ISO 10336:1997 is intended for:
- Petroleum laboratories performing quality control and acceptance testing of crude oil.
- Refinery laboratories, pipeline operators and custody‑transfer inspectors who need accurate water content data.
- Analytical chemists and testing service providers validating homogenization and titration procedures for crude feeds.
Practical benefits include reliable, direct water measurements suitable for process control, contract testing and troubleshooting emulsions or water ingress in storage and transfer systems.
Related standards
Normative references in ISO 10336 include:
Keywords: ISO 10336:1997, Karl Fischer titration, crude petroleum water determination, potentiometric titration, water content analysis, pyridine‑free Karl Fischer, sample homogenization.