Overview
ISO 10337:1997 specifies a coulometric Karl Fischer titration method for the direct determination of water in crude petroleum. The method covers typical oil laboratory practice, defining sampling, sample handling, apparatus, reagents and the titration procedure. It is intended for water contents in the range from about 0.02 % to 5.00 % (m/m) depending on the level of interfering sulfur species (mercaptans or ionic sulfides). The standard also includes a normative Annex A on sample handling and an informative Annex B describing an alternative volumetric test-portion measurement.
Key topics and requirements
- Principle: water is quantified by coulometrically generated iodine; water moles = integrated charge (Faraday’s law).
- Measurement ranges:
- 0.050 %–5.00 % (m/m) when mercaptan/sulfide S ≤ 0.05 % (m/m)
- 0.020 %–5.00 % (m/m) when mercaptan/sulfide S ≤ 0.005 % (m/m)
- Interferences: mercaptans and ionic sulfides are called out as the main potential interferences; limits for insignificant interference are specified.
- Apparatus and reagents: automatic coulometric Karl Fischer titrator, non‑aerating mixer, xylene (reagent grade), commercial KF anolyte and catholyte; recommended syringe sizes (10 µl, 250 µl, 1 ml), balance with ±0.1 mg resolution and thermometer (±1 °C).
- Sample handling: follow ISO 3170/3171 sampling; homogenize immediately before analysis and record temperatures before/after mixing (temperature rise must not exceed 10 °C).
- Quality control: perform 10 µl water injections to check reagent response (initially and typically after every ~10 test portions); replace electrolytes on off-spec checks, high/unstable background current, phase separation or oil contamination.
- Calculation: water % (m/m) is computed from mass of water displayed by titrator (µg) and mass of test portion (g) - convert µg to g and express as percentage.
- Precision: the standard provides repeatability and reproducibility performance data (e.g., at 1.00 % (m/m) r = 0.04 % and R = 0.11 %).
Applications and users
ISO 10337 is used by:
- Petroleum and refinery quality-control laboratories
- Custody-transfer and blending operations requiring accurate water content data
- Inspection and testing bodies monitoring crude oil shipments
- R&D and process labs validating moisture control or dehydration processes
Key practical benefits: fast, direct water determination in crude streams, traceable QC checks, clear limits for interferences and precision - enabling reliable decisions on treatability, transportability and quality acceptance.
Related standards
Normative references include:
Keywords: ISO 10337, Karl Fischer titration, coulometric Karl Fischer, water determination in crude oil, crude petroleum water content, petroleum laboratory standard.