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 you profit from
the following advantages:
- 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. |
