Overview
ISO 4327:1979 specifies a laboratory method for determining the hydroxyl value of polyalkoxylated non‑ionic surface‑active agents (surfactants) using the phthalic anhydride method. The method esterifies hydroxyl groups with phthalic anhydride in pyridine, hydrolyzes unreacted anhydride with the water present in the sodium hydroxide neutralizing solution, then quantifies the acid formed by titration with standard sodium hydroxide using phenolphthalein. The hydroxyl value is reported as milligrams of potassium hydroxide equivalent per gram (mg KOH/g).
Key topics and requirements
- Scope and applicability: Designed for polyalkoxylated condensates of aliphatic and alicyclic compounds (EO/PO adducts of fatty alcohols, alkylphenols, fatty acids) for hydroxyl values roughly 10–1 000 mg KOH/g.
- Analytical principle: Esterification → hydrolysis of excess anhydride → neutralization/titration. The hydroxyl value is calculated from the difference between NaOH volumes for blank and test solutions.
- Reagents and apparatus: phthalic anhydride in pyridine (phthalation reagent), standard volumetric NaOH (0.5 N), phenolphthalein indicator, condensers, burettes and ground‑glass flasks; only analytical‑grade reagents and distilled water are used.
- Sample handling: Test portion mass depends on estimated hydroxyl value and sample water content (table given in annex B). Water content should be known (ISO 4317 referenced).
- Interferences and limitations: Primary/secondary amines, amides, tertiary alcohols, thiols, epoxides and long‑chain fatty acids/esters can react and falsify results. Corrections or alternate prep (e.g., epoxide removal by cold vacuum distillation) may be required.
- Safety: Pyridine and phthalic anhydride are toxic - operations must be in a well‑ventilated fume hood or use the special apparatus in Annex C for hoodless operation.
- Performance: Precision reported as ~1.5% (rounding recommendations and inter‑laboratory reproducibility data are provided).
Practical applications and users
- Who uses it: QC and R&D laboratories in surfactant and detergent manufacturing, chemical suppliers, formulation chemists, and analytical labs verifying polyalkoxylated surfactant composition.
- Why it’s useful: Hydroxyl value informs degree of alkoxylation, functionality for reactions (e.g., polyurethane or ester synthesis), quality control of non‑ionic surfactants, batch consistency and regulatory/labeling documentation.
- When to apply: Routine QC testing, incoming raw material inspection, failure analysis when performance deviates, or when hydroxyl group quantification is needed for downstream chemistry.
Related standards
- ISO 4317 - Determination of water content (Karl Fischer)
- ISO 4314 - Determination of free alkalinity or acidity (titrimetric)
- ISO 607 - Sample division for surface active agents
- ISO 2211 - Measurement of liquid chemical product colour (Hazen units)
- ISO 1392 - Melting point determination (used for reagent verification)
Keywords: ISO 4327, hydroxyl value, phthalic anhydride method, non‑ionic surface active agents, polyalkoxylated derivatives, surfactant analysis, titration, pyridine, phenolphthalein, sodium hydroxide.
Open preview (PDF)Non-ionic surface active agents — Polyalkoxylated derivatives — Determination of hydroxyl value — Phthalic anhydride method