Metrohm electrode detects ionic surfactants

The Metrohm High Sense surfactant electrode is a PVC membrane electrode with a membrane composition (ionophore/plasticiser) specially optimised for the determination of ionic surfactants.

Surfactants are crucial constituents in cosmetics, detergents, cleansers and pharmaceuticals.

Whether in formulations or starting materials - the content should be determined quickly and accurately.

The usual two-phase titration employs chloroform and, in several cases, the titration endpoint can be detected only with difficulty and the titration cannot be automated.

The potential is formed by a specific interaction between the ion carrier incorporated in the PVC membrane and the analyte ions (surfactants) in the sample solution.

This interaction produces an electrical potential difference at the phase boundary sample solution/membrane that can be measured against a reference electrode.

The High Sense surfactant electrode has a working life of about one year or around 10,000 titrations, but should not come into contact with organic solvents such as acetone, tetrahydrofuran and chloroform.

The Metrohm Titrandos and Titrino-Plus titrators can be used for the determination of ionic surfactants.

The choice of titrant is also important.

The lower the solubility of the compounds formed, the steeper and more pronounced the potential jumps.

The titrants are preferably used as 0.004mol/l solutions.

For anionic surfactants, the Tego trant A 100 titrant, available from Metrohm, has proved useful, whereas for cationic surfactants, sodium dodecylsulphate (Merck 12533 or Fluka 71727) is normally used.

A large number of practical titrations have been performed in the Metrohm application laboratory.

These are described in Application Bulletin No 233, which is available free from Metrohm.

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