Determination of anionic and cationic surfactants by potentiometric two-phase titration

Significance of the topic

The measurement of surfactant levels is crucial in quality control of personal care, detergents and industrial formulations. Traditional manual methods are hazardous and time consuming. A robust, automated potentiometric approach can streamline analysis and improve safety and precision across diverse sample matrices.

Objectives and Study Overview

This study evaluates a potentiometrically indicated two-phase titration method using solvent-resistant surfactant electrodes (Surfactrodes) for quantifying anionic and cationic surfactants. Samples analyzed include hair conditioners, washing powders, bath oils and industrial cleaners. Results are compared to the classical Epton titration (ISO 2271).

Methodology

The potentiometric two-phase titration follows DIN EN 14480 and DIN EN 14468. A defined sample volume is mixed with a water/solvent phase (methyl isobutyl ketone/ethanol 1:1 v/v) and an emulsifier. Titration under constant stirring is performed with titrants specific to surfactant type (SDS for anionic, Hyamine 1622 or imidazolium chloride for cationic). The equivalence point is detected by Surfactrode-sensitive electrodes, replacing the use of toxic chloroform and manual endpoint recognition.

Used Instrumentation

• 809 Titrando automatic titrator
• 804 Ti Stand modular titration stand
• 802 Stirrer for high-speed agitation
• 800 Dosino dosing unit
• Surfactrode Resistant and Surfactrode Refill electrodes
• Ag/AgCl reference electrode (3 mol/L KCl)

Main Results and Discussion

• Excellent agreement with classical Epton titration; relative standard deviations below 2.1% across all sample types.
• Measured surfactant concentrations: hair conditioners (~7.4 mmol/100 g cationic), washing powders (~30 mmol/100 g anionic), bath oils (~52.5 mmol/100 g anionic), industrial cleaners (~11 mmol/100 g anionic).
• No interference from fats, oils or strong oxidizers in complex matrices.
• Significantly shorter analysis times and full compatibility with automation.

Benefits and Practical Applications

• Use of non-toxic, environmentally friendly solvents enhances laboratory safety.
• Automated potentiometric endpoint detection improves precision and repeatability.
• Suitable for routine quality control in cosmetics, household and industrial products.
• Flexible method adaptable to different surfactant chemistries and product matrices.

Future Trends and Possibilities

Advances may include miniaturized, flow-through titration platforms and integration with inline process analytics. New universal surfactant sensors could extend applications to mixed formulations and environmental monitoring. Machine learning–driven titration protocols may offer real-time optimization and decision support in manufacturing and quality control.

Conclusion

Potentiometric two-phase titration with organic-solvent-resistant electrodes offers a fast, precise and eco-friendly alternative to conventional manual methods for surfactant analysis. Its high reproducibility and seamless automation make it an ideal choice for modern analytical laboratories.