Overview
ISO 4314:1977 - Surface active agents - Determination of free alkalinity or free acidity - Titrimetric method specifies a simple volumetric titration to quantify the free alkalinity (alkali value) or free acidity (acid value) of surface‑active agents (surfactants). The method uses an ethanolic or propan‑2‑ol solution of the product, phenolphthalein as indicator, and standard 0.1 N volumetric solutions of potassium hydroxide (KOH) or hydrochloric/sulphuric acid (HCl/H2SO4) as appropriate. Results are reported as milligrams of KOH per gram of product.
Key topics and requirements
- Scope: Applicable to surfactants where the product-specific standard indicates this test.
- Principle: Volumetric titration of a dissolved test portion in ethanol (95% v/v) or isopropanol (50% v/v) with standard acid or base in the presence of phenolphthalein.
- Reagents (examples given in the standard):
- Ethanol 95% v/v or propan‑2‑ol 50% v/v (neutralized)
- Potassium hydroxide, 0.1 N standard volumetric solution
- Hydrochloric acid or sulphuric acid, 0.1 N standard volumetric solution
- Phenolphthalein solution (10 g/L in 95% ethanol)
- Apparatus:
- 250 mL conical flask
- 25 mL Class A burette
- Ordinary laboratory glassware per referenced ISO apparatus requirements
- Procedure highlights:
- Weigh ~10.000 g test portion (to 0.001 g).
- Dissolve in solvent, add phenolphthalein, reflux briefly to remove CO2, cool.
- If solution is colourless → titrate with KOH (determine alkalinity).
- If solution is pink → titrate with HCl or H2SO4 (determine acidity).
- Expression of results: Alkali or acid value expressed as mg KOH/g using the formula:
- Alkali/acid value = (V × T × 56.1) / m
- V = volume (mL) of standard solution used
- T = exact normality of the standard solution
- m = mass (g) of test portion
- Reporting: Include sample ID, method reference, results, test conditions and any deviations or incidents.
Applications and users
- Practical for quality control, batch release and stability testing of surfactants and detergents.
- Used by:
- Surfactant and detergent manufacturers
- Formulation chemists and R&D labs
- Third‑party testing and certification laboratories
- Regulatory and conformity assessment bodies checking product specifications
- Typical uses: monitoring free alkali/acidity that affects product performance, skin irritation potential, corrosion, and formulation compatibility.
Related standards
- ISO 607 - Surface active agents - Detergents - Methods of sample division (sampling instructions referenced)
- ISO 1773 - Laboratory glassware/conical flask requirements (instrument compliance)
- ISO 385 - Burette class A specifications (volumetric apparatus)
- Prepared by ISO/TC 91 (Surface active agents)
Keywords: ISO 4314:1977, surface active agents, titrimetric method, free alkalinity, free acidity, phenolphthalein, potassium hydroxide, volumetric titration, alkali value, acid value, surfactant testing.
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