Titer determination in potentiometry

Significance of the topic

Potentiometric titration is a fundamental technique in analytical chemistry, offering precise endpoint detection without reliance on visual indicators. Determination of titrant concentration (titer) under real measurement conditions ensures accuracy in subsequent analyses across acid–base, complexometric, precipitation, and redox titrations.

Objectives and overview

This document outlines Metrohm AG’s recommended procedures for establishing the titer of common volumetric titrants. It aims to align titer determination protocols with actual analytical applications by specifying suitable primary standards, electrode systems, and titration conditions.

Methodology and Instrumentation

Procedures involve poteniometric titration using automated titrators equipped with:

• Precision burets (10 or 20 mL)
• Stirring units (optionally with sample changers)
• Electrode systems tailored to the titration type (combined pH, solvent or metal ion selective, and platinum or gold ring electrodes)

Primary standard substances are selected for high purity, stability, and traceability. They are dried at defined temperatures before use and dissolved in appropriate media to match titrant chemistry and solvent systems.

Main results and discussion

Recommended pairings of titrants, standards, and electrodes include:

• Acid–base titrations: TRIS or potassium hydrogen phthalate (KHP) with combined pH electrodes in aqueous, glacial acetic acid, or alcohol media.
• Complexometric titrations: Calcium carbonate standard titrated with EDTA using a calcium ion-selective electrode at pH 10.
• Precipitation titrations: Sodium chloride with silver nitrate using silver ring electrodes.
• Redox titrations: Sodium oxalate with cerium(IV) at 60 °C; thiosulfate with iodine using platinum electrodes; permanganate with oxalate optionally catalyzed by Mn(II); nitrite with sulfanilic acid monitored by gold ring electrodes.

Key factors influencing precision include sample size (>100 mg recommended), preparation of stock solutions to minimize weighing errors, and selection of supporting electrolytes to stabilize electrode response.

Benefits and practical applications

Adhering to these titration standards enhances reproducibility and traceability in quality control laboratories, research settings, and industrial processes. Potentiometric endpoints eliminate subjective color change interpretation, enabling automated workflows and improved throughput.

Future trends and potential applications

Advances may include miniaturized and wireless sensors for inline monitoring, integration of machine-learning algorithms for endpoint detection, and development of novel robust electrode materials for challenging solvents and complex matrices.

Conclusion

Implementing standardized potentiometric titer determination under matched analytical conditions ensures reliable titrant concentration data, forming the basis for accurate volumetric analyses across diverse chemical applications.

References

• Jander G., Jahr K.F. Massanalyse: Theorie und Praxis der Titrationen mit chemischen und physikalischen Indikationen. Walter de Gruyter, 2003.
• Metrohm Monographs: Electrodes in potentiometry; Practical aspects of modern titration; Practical titration.
• Various Metrohm Application Bulletins.
• Merck Spectrum Special Issue: Titration and Electrochemistry.
• Scholz E. HYDRANAL Manual for Karl Fischer titration reagents. Sigma-Aldrich, 2010.