ISO 6296:2000

Overview

ISO 6296:2000 specifies a potentiometric Karl Fischer titration method for the direct determination of water in petroleum products. The method is intended for products boiling below 390 °C and covers a mass-fraction water range of 0.003 % (m/m) to 0.100 % (m/m). The International Standard includes requirements for reagents, apparatus, sampling and sample preparation (including a normative Annex A on homogenization), titration procedure, calculation, expression of results and precision.

Key topics and technical requirements

• Principle: direct titration of a weighed sample to a potentiometric end-point using Karl Fischer reagent; non-clear samples require surfactant treatment and homogenization.
• Scope limits: validated for products boiling below 390 °C; may be applied to heavier products and base oils but precision is not established for those.
• Reagents:
  • pyridine-containing, pyridine-free, and ketone-formulated Karl Fischer reagents (nominal ~5 mg H2O/ml; minimum 3 mg/ml when checked).
  • molecular sieve (4A) for drying xylene; dry methanol, N‑ethyl piperidine, and sodium dioctylsulfosuccinate solution for problematic samples.
• Titration solvent systems are specified for each reagent type (mixtures with dry xylene and amine/methanol components).
• Apparatus: potentiometric Karl Fischer titrator, non‑aerating mixer for homogenization, glass syringes with fine needles, balance (±0.1 mg), ovens, cooling bath and thermometer.
• Sampling & preparation: sample handling per ISO 3170 / ISO 3171; visual inspection (clear/bright), mixing parameters and temperature rise limits (mixing should not raise sample temperature by >2 °C).
• Standardization: Karl Fischer reagents must be standardized daily using known water additions and titration to a steady potentiometric end-point.
• Interferences: hydrogen sulfide and mercaptans can interfere; concentrations below 0.003 % (m/m) sulfur are not significant for the defined water range. Many common sulfur compounds (sulfides, disulfides, thiophenes) do not interfere.