Potentiometric determination of ionic surfactants by two-phase titration using Surfactrodes

Significance of Topic

The reliable quantification of ionic surfactants is critical in industries such as detergents, cosmetics, pharmaceuticals and electroplating. Potentiometric two-phase titration using Surfactrodes offers automated, rapid and environmentally friendly determination of anionic and cationic surfactants without the need for toxic chloroform extraction.

Objectives and Overview

This bulletin presents a unified method for potentiometric two-phase titration of ionic surfactants. It describes selection and preparation of titrants, pH control for selective group titration, solvent systems and comparison with classical Epton titration results.

Methodology and Instrumentation

The method uses a Metrohm titrator in DET mode, 20 mL buret, a rod stirrer for intensive mixing and two surfactant electrodes (Surfactrode Resistant and Refill) with Ag/AgCl reference. Anionic surfactants are titrated with TEGO trant A100, while cationics use sodium dodecyl sulfate standard. Solvents such as methyl isobutyl ketone, n-hexane and ethanol, plus TEGO add, enhance phase separation and curve quality. Precise pH adjustment (pH 2–12) enables selective determination of sulphonate, carboxylate or quaternary groups.

Main Results and Discussion

The Surfactrode approach yields titration curves with steep, reproducible potential jumps and relative standard deviations near 1 %. Data correlate closely with classical Epton titrations. The method accommodates raw surfactant materials, concentrated shampoos, lubricants, household cleaners and washing powders with both soluble and insoluble builder systems.

Benefits and Practical Applications

• High automation and reproducibility in routine QA/QC
• Elimination of carcinogenic chloroform
• Broad applicability to complex formulations
• Analysis time of 5–10 minutes per sample
• Minimal sample preparation and simple electrode maintenance

Future Trends and Potential Uses

Advances may include integration with robotic sample handling and in-line process monitoring. Development of more selective titrants and electrode coatings could extend the method to amphoteric and betaine surfactants. Green solvent systems and enhanced data processing will further streamline workflows.

Conclusion

Potentiometric two-phase titration with Surfactrodes provides a fast, accurate and eco-friendly alternative for ionic surfactant analysis. It matches traditional accuracy while simplifying sample preparation and eliminating hazardous solvents.

Instrumentation Used

• Metrohm titrator with DET mode
• 20 mL buret
• Propeller rod stirrer
• Surfactrode Resistant and Surfactrode Refill electrodes
• Ag/AgCl reference electrode

References

1. R. Schulz, “Titration of Surfactants and Pharmaceuticals,” Ziolkowsky, Augsburg, 1996.
2. R. Schulz, R. Gerhards, “New Surfactrodes for Ionic Surfactants,” LaborPraxis 20/10 (1996) 74–76.
3. R. Schulz, J. Thiede, “Surfactant Titration in Coolants,” LaborPraxis 21/11 (1997) 64–68.
4. Metrohm Application Bulletin No. 233, “Titrimetric Determination of Surfactants.”
5. Metrohm Application Bulletin No. 275, “Two-Phase Titration in Washing Powders.”