New DIN/EN standard for determining anionic surfactants by means of potentiometric two-phase titration is faster and more precise than Epton titration, and is healthier for analysts
The determination of the content of surface-active agents (surfactants) plays an important role in many sectors - from wastewater analysis up to quality control in production processes.
A method that is still in widespread use is the so-called Epton titration according to ISO 2271, a complicated and time-consuming manual titration.
The new DIN EN 14480 standard now describes an alternative determination method that is much simpler and faster: potentiometric two-phase titration.
Potentiometric two-phase titration according to DIN EN 14480: more precise, faster, and much healthier.
The solution of the anionic surfactant is pipetted into a titration vessel, to which a two-phase mixture of water and methyl isobutyl ketone/ethanol 1:1 and an emulsifier are added.
Under vigorous stirring the emulsion formed is titrated with a cationic surfactant, in this case benzethonium chloride (Hyamine 1622).
The ion pair formed, which is insoluble in water, is extracted immediately into the organic phase.
The determination of the equivalence point does not take place visually, but potentiometrically using surfactant-sensitive electrodes.
The Surfactrodes from Metrohm are used for this purpose; they have a high affinity for surface-active agents.
In comparison with the Epton titration, several advantages will be seen:.
Use of unproblematic solvents instead of chloroform.
Short determination times: only a few minutes per titration.
Objective, computer-supported determination of the equivalence point and therefore improved precision.
Can easily be automated.
In an extensive Europe-wide interlaboratory test the potentiometric two-phase titration was compared with the Epton method and was found to yield the same analytical results with a better repeatability.
A detailed evaluation of the interlaboratory test can be found in the appendix of DIN EN 14480.
