Determination of Salts of Carboxylic Acids by Aqueous Acidometric Titration

Significance of the Topic

Accurate determination of carboxylate salts is crucial in pharmaceutical, food, and chemical industries where compound purity impacts performance and safety. Thermometric titration combines simplicity and sensitivity by monitoring heat changes during acid-base reactions, offering a rapid alternative to conventional techniques.

Objectives and Study Overview

This study outlines a thermometric titration method for quantifying sodium and potassium carboxylate salts in aqueous solutions. The primary goals are to establish reliable endpoint detection using a thermochemical indicator and to evaluate method suitability for assessing reagent purity.

Methodology

• Principle: Protonation of RCO2− with hydrochloric acid generates a small exothermic heat change. Adding sulfate ions amplifies thermal inflections due to its endothermic protonation heat, improving endpoint clarity.
• Reagents: 2 mol/L HCl as titrant; 10 % Na2SO4 solution as thermochemical indicator.
• Sample Preparation: Weigh or pipette approximately 10 mmol of RCO2Na or RCO2K into a titration vessel, add 2 mL of sulfate indicator, and dilute to ~30 mL with deionized water.
• Titration Parameters:
  • Titrant delivery rate: 4 mL/min
  • Number of exothermic endpoints: 1
  • Data smoothing factor (DSF): 45
  • Stirring speed: 10 rpm (802 stirrer)

Used Instrumentation

• Thermometric titrator equipped with sensitive temperature sensor and controlled acid dosing.
• Magnetic stirrer (model 802) to ensure uniform mixing.
• Analytical balance and calibrated pipettes for precise sample and reagent handling.

Key Results and Discussion

The method was validated using sodium acetate trihydrate. Results showed an average purity of 98.93 ± 0.04 % (n=7), demonstrating high accuracy. Temperature vs volume titration curves exhibited clear exothermic inflections, while second derivative plots enhanced endpoint detection. The blank correction ensured reliable quantification.

Benefits and Practical Applications

• Rapid and precise quantification of carboxylate salts without complex sample pretreatment.
• Applicable for quality control of raw materials in pharmaceuticals and food additives.
• Minimal reagent consumption and straightforward data interpretation.

Future Trends and Opportunities

Advancements may include integration with automated sample changers and miniaturized devices for high-throughput screening. Combining thermometric titration with chemometric data analysis could further enhance sensitivity and endpoint resolution for complex matrices.

Conclusion

Thermometric titration using sulfate as a thermochemical indicator provides a fast, accurate, and robust approach for determining sodium and potassium salts of carboxylic acids. The method’s simplicity and reliability make it a valuable tool for routine purity assessments.

References

1. J. Christensen et al. Experiments in thermometric titrimetry and titration calorimetry. Brigham Young University, 1974.