Total acid number with conductometric titration

Significance of topic

The total acid number (TAN) is a critical indicator of acidity in petroleum-based lubricants and engine oils. Elevated TAN values can accelerate corrosion, impair equipment performance, and reduce service life. Routine monitoring of TAN supports preventive maintenance and ensures optimal function in industrial and automotive applications.

Objectives and overview

This study demonstrates a conductometric titration method for determining the TAN of sliding track oil. The aim is to showcase an automated, precise, and sensitive approach that eliminates the need for visual indicators and simplifies sample handling.

Methodology and instrumentation

A sample of sliding track oil was titrated with potassium hydroxide dissolved in 2-propanol. Conductometric titration was performed until the first equivalence point, with conductivity changes tracked continuously. The OMNIS Titrator platform, featuring automated dosing and sample handling, provided controlled reagent addition and real-time data acquisition.

Used instrumentation

• OMNIS Titrator with dosing module and sample robot
• OMNIS Conductivity Measuring Module
• 5-ring conductivity measuring cell (cell constant 0.7 cm⁻¹) with integrated Pt1000 temperature sensor

Main results and discussion

Triplicate determinations of the sliding track oil yielded a mean TAN of 0.40 mg KOH/g with a relative standard deviation (RSD) of 1.1 %. The conductometric titration curve exhibited a sharp inflection at the equivalence point, confirming accurate endpoint detection and method precision.

Benefits and practical applications

• No requirement for color indicators or complex sample preparation
• High sensitivity suitable for highly diluted or nonaqueous samples
• Adaptable to various sample matrices including solutions, suspensions, and slurries
• Automated cleaning and rapid analysis enhance laboratory throughput

Future trends and possibilities

Advances in automation, integration with inline sensors, and coupling with data analytics will enable real-time TAN monitoring in production environments. Development of multi-parameter titration systems may further expand applications across petrochemical processing and quality control.

Conclusion

Conductometric titration using the OMNIS platform offers a robust, accurate, and user-friendly method for TAN determination in petroleum products. Its automation and versatility make it ideally suited for routine quality assurance and research laboratories.

Reference

Metrohm Application Note AN-T-240