Potentiometric and thermometric determination of boric acid

Importance of the Topic

Control of boric acid concentration is essential in nuclear power plant primary circuits, electroplating baths and fertilizer production. Reliable quantification ensures process safety, quality control and environmental compliance, given boron's role in corrosion inhibition, neutron absorption and plant nutrition.

Study Objectives and Overview

This bulletin compares two titrimetric approaches for boric acid determination:

• Potentiometric titration enhanced by polyalcohol complexation (mannitol method)
• Thermometric titration via exothermic fluoride reaction

It outlines sample preparation, titration parameters and calculation procedures for both methods.

Methodology and Instrumentation

• Potentiometric determination
  
  • Titrator with direct endpoint detection
  • Ecotrode Plus pH electrode
  • 0.1 mol/L NaOH titrant and saturated mannitol solution
• Thermometric determination
  
  • Thermometric titrator with Thermoprobe HF sensor
  • 1 mol/L KF titrant and 5 mol/L HCl acidification

Both methods require CO₂-free reagents and minimal sample preparation.

Main Results and Discussion

Potentiometric titration:

• Mannitol forms stronger acid complexes with boric acid, yielding sharp pH jumps at equivalence.
• Calibration via potassium hydrogen phthalate standard gives a titrant correction factor.
• Interference from medium acids (e.g., phosphates) can limit selectivity.

Thermometric titration:

• Fluoride reacts exothermically with H₃BO₃ in acidic medium, producing well-defined thermal endpoints.
• Stoichiometric calibration by linear regression of standard additions defines titer and method blank.
• Metal ions do not interfere, but acid ratio must be held constant for reproducible curves.

Benefits and Practical Applications

• Potentiometric method offers rapid, low-cost analysis in fertilizer, plating and glass industries.
• Thermometric approach delivers high selectivity in complex matrices, including nuclear primary water.
• Both methods are automatable for routine quality assurance in industrial and research labs.

Future Trends and Possibilities

• Integration with flow-through systems for real-time monitoring.
• Development of solid-state sensors for on-site process control.
• Coupling with spectroscopic detection to differentiate boron species in complex matrices.

Conclusion

Both potentiometric and thermometric titrations provide robust, accurate routes for boric acid quantification. Choice of method depends on sample matrix, required selectivity and instrumentation availability. Implementing these techniques supports critical process monitoring across nuclear power, electroplating and fertilizer production.

Reference

1. Jander G., Jahr K.F. Massanalyse, 15th ed. Walter de Gruyter, 1989.
2. Csapo F., Bihari M., Gilde M., Sztanko E. Quantitative microdetermination of boron by pH measurement of mannitol-boric acid complex, Fresenius Journal of Analytical Chemistry, 151(4), 273–276.
3. Miller F.J., Thomason P.F. Direct thermometric titration of boric acid, Talanta, 2(2), 109–114.