Overview
ISO 2871-2:2010 specifies an analytical titration method for determining the content of low‑molecular‑mass cationic-active matter (molar mass between 200 and 500) in detergents and surfactant products. The standard covers monoamines, amine oxides, quaternary ammonium compounds and alkyl‑pyridinium salts that have a main hydrocarbon chain of 10–22 carbon atoms (and no more than six other carbon atoms in the cation). The method applies to solid materials or aqueous solutions when the relative molecular mass is known or estimated, and it is not applicable where anionic and/or amphoteric surfactants are present.
Key topics and requirements
- Principle: biphasic (water–chloroform) titration using an anionic standard (sodium laurylsulfate) and a mixed dye indicator (acid blue 1 with dimidium bromide). Cationic surfactants form colored ion pairs that migrate to the chloroform layer; end point is a color change from blue to pale grey‑pink.
- Reagents & concentrations: typical reagents include chloroform (ρ ≈ 1.48 g·ml−1, specified distillation range) and a sodium laurylsulfate titrant (prepared and purity‑checked; example concentration ~0.004 mol·L−1).
- Indicator system: preparation of a mixed indicator (acid blue 1 and dimidium bromide), with an acidic indicator solution for use in the biphasic titration.
- Sampling and sample size: laboratory sample preparation per ISO 607; sample mass selected to contain about 0.002–0.003 mol of cationic active matter (guidance table uses an example M = 360).
- Procedure parameters: common procedural volumes from the standard - 25 ml aliquot, 10 ml indicator solution, 15 ml chloroform - and titration to disappearance of the blue color in the chloroform phase.
- Calculations & reporting: formula to convert titrant volume to mass % cationic-active matter (requires titrant concentration and molecular mass of the active). Precision statements: repeatability ~1.6% and reproducibility ~4% (relative to mean).
- Limitations: method is unsuitable in presence of interfering anionic or amphoteric surfactants; some hydrotropes and non‑ionic components may not interfere under specified limits.
Applications and users
- Quality control and batch release testing in detergent and surfactant manufacturing
- Raw‑material verification and incoming goods inspection for cationic surfactants
- Analytical and contract laboratories performing surfactant content assays
- R&D and formulation teams assessing cationic active content in rinse aids, fabric softeners, antimicrobial agents and similar products
- Regulators and standards bodies referencing a validated method for product compliance
Related standards
Keywords: ISO 2871-2:2010, cationic-active matter, detergents, surfactants, titration, sodium lauryl sulfate, low molecular mass, analytical method, quality control.