EN 14668:2005 – Surface active agents – Determination of quaternary ammonium surface active agents in raw materials and formulated products – Potentiometric two-phase titration method

1 Scope
This European Standard specifies a method for the determination of the content of quaternary ammonium surface active agents in raw materials and formulated products, defined as being the amount of quaternary ammonium surface active agents expressed in millimoles per 100 g of product.
NOTE 1 The applicability in products different than those tested should be checked in each particular case.
NOTE 2 In comparison to usual laboratory two-phase titration with visual endpoint determination (see ISO 2871-1 and ISO 2871-2) potentiometric titration offers the advantage of automation, operator-dependent differences in recognising the equivalence point can be neglected, and a non-critical solvent replaces the toxicologically critical chloroform.
2 Normative references
The following referenced documents are indispensable for the application of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies. EN 14670, Surface active agents – Sodium dodecyl sulfate – Analytical method.
EN ISO 3696, Water for analytical laboratory use- Specification and test methods (ISO 3696:1987). ISO 607, Surface active agents and detergents-Methods of sample division.
3 Principle Quaternary ammonium surface active agents are combined with anionic surface active agent to form water-insoluble ion pairs which are immediately extracted into a water immiscible organic solvent. This fundamental reaction is the basis for the titration of equivalents of ionic surface active agents with an oppositely charged surface active agent standard volumetric solution in the two-phase titration.
This process is supported by intensively stirring the two-phase mixture of aqueous solution and organic phase. The potential, which is formed in the emulsion during the titration, is recorded with the help of a special solvent-resistant surface active agent-sensitive electrode in combination with a silver/silver chloride reference electrode against the amount of titrant added. The equivalence point of the added anionic surface active agent corresponds to that one of the test solution at the inflection point of the titration curve (Annex B).
4 Reagents WARNING — Your attention is drawn to the regulations covering the handling of hazardous substances. Technical, organisational and personal protection measures should be observed.
During the analysis, unless otherwise specified, use only reagents of recognized analytical grade that have been checked in advance as to not interfere with the analytical results.
4.1 Water, complying with grade 3 as defined in EN ISO 3696. NOTE If the water is purified via ion-exchange resins, ensure that no cationic or anionic species from the resins cause interference.
4.2 Sodium dodecyl sulfate, C 12 H 25 OSO 3 Na, % (m/m)(C 12 H 25 OSO 3 Na) ≥ 99 as determined following the method EN 14670.
EN 14668:2005 – Surface active agents – Determination of quaternary ammonium surface active agents in raw materials and formulated products – Potentiometric two-phase titration method