Overview
EN 15168:2006 is a CEN standard for the determination of hydroxyl value (OHV) of aliphatic and cyclic hydroxyl compounds using the p-toluenesulfonyl isocyanate (TSI) method followed by potentiometric titration with tetrabutylammonium hydroxide (TBAH) in a non‑aqueous medium. The method quantifies milligrams of KOH equivalent per gram of sample and is intended for many surfactant and polyol matrices, including temperature‑sensitive materials and high‑solids polymer polyols.
Key topics and requirements
- Scope and limitations
- Applicable to hydroxyl groups attached to primary and secondary carbon atoms.
- Not suitable for hydroxyl groups on tertiary carbons.
- Recommended for neutral refined products; samples with excess acidic/basic species require validation to confirm no interference.
- Analytical principle
- Sample reacts with excess TSI to form an acidic carbamate; residual isocyanate is hydrolyzed, then the acidic carbamate is titrated potentiometrically with TBAH.
- Sample preparation
- Follow ISO 607 for sampling and division; heat solid samples only to the minimum temperature required to melt and homogenize.
- Reagents and safety
- Key reagents: TSI, acetonitrile, THF, toluene, and TBAH standard solution.
- Warning: several reagents (acetonitrile, TSI, TBAH) are hazardous-work in a fume hood and follow laboratory safety procedures.
- Apparatus and measurement
- Use an automatic potentiometer with dynamic dosing and suitable electrodes for non‑aqueous titration (combined glass electrode or separate pH/reference electrodes with appropriate electrolytes).
- Calculations, precision and reporting
- OHV calculated from the volume difference between titration end points; results expressed with defined decimal precision.
- The standard defines repeatability and reproducibility concepts and requires duplicate determinations and full reporting of deviations.
Applications - who uses this standard
- Quality control and R&D laboratories in:
- Surfactant and detergent manufacturing
- Polyol and polyurethane supply chains (rigid and high‑solids polyols)
- Polymer chemistry and specialty chemicals producers handling polyacetals or temperature‑sensitive materials
- Analytical service labs offering OHV testing for raw materials, in‑process samples and finished products where accurate hydroxyl quantification is required for formulation and stoichiometry.
Related standards
- EN ISO 3696 - Water for analytical laboratory use (used for reagent water quality).
- ISO 607 - Sample division for surface active agents.
- EN 13926 - Alternate methods referenced for products with interfering acidic/basic species (validation guidance).
Keywords: EN 15168:2006, hydroxyl value, TSI method, p-toluenesulfonyl isocyanate, potentiometric titration, tetrabutylammonium hydroxide, surface active agents, polyols, non‑aqueous titration, CEN.