Monograph

Importance of thermometric titrimetry

Thermometric titrimetry offers an objective and highly precise way to locate titration endpoints by measuring the heat released or absorbed during chemical reactions. This method overcomes limitations of indicator-based titrations and potentiometric approaches, delivering rapid results with minimal sensor maintenance. It is particularly valuable in industrial and quality control laboratories for a wide range of chemistries and sample matrices.

Objectives and overview of the monograph

The monograph aims to introduce practicing industrial analytical chemists to:

• The theoretical foundation of thermometric titrimetry
• Practical setup and optimization of automated systems
• Calibration procedures and method blank determination
• Diverse applications covering acid–base, redox, complexometric, precipitation and water analysis

Methodology and instrumentation

The core setup comprises a thermistor-based sensor (Thermoprobe), precision dosing units (800 Dosino), a stirred titration vessel, an interface module (859 Titrotherm) and PC software. Critical parameters include:

• Efficient mixing at high stirring rates to minimize temperature gradients
• Optimal probe orientation relative to reagent delivery
• Adjustable data sampling rate (5–25 points per second) and digital smoothing to sharpen endpoint detection
• Determination of titrant concentration and method blank via regression of standard solutions

Main results and discussion

Theoretical comparison shows thermometric titrations detect enthalpy changes larger than free energy changes used in potentiometry, yielding sharper endpoints. Practical applications illustrate:

1. Acid–base titrations
   
   • Strong acid–strong base, weak acids, mixed acids and non-aqueous systems
   • Catalyzed endpoints using paraformaldehyde for trace acid determination in oils
2. Redox titrations
   
   • Permanganate and dichromate titrations of FeII and H2O2
   • Thiosulfate and hypochlorite titrations
3. Complexometric titrations with EDTA
   
   • Direct CaII/MgII determinations and back-titrations for CoII/NiII
   • Catalytically enhanced endpoints for trace metal analysis
4. Precipitation titrations
   
   • Sulfate with BaII, aluminum with fluoride, orthophosphate with MgII
   • Nickel, anionic/cationic surfactants and non-ionic surfactant analyses
5. Water determination
   
   • Karl Fischer alternative using 2,2-dimethoxypropane or triethyl orthoformate

Reaction enthalpies ranging from strong exotherms to endotherms influence endpoint sharpness. Well-designed software smoothing and second-derivative algorithms allow precise endpoint localization with coefficients of variance often below 0.1%.

Benefits and practical applications of the method

• Objective endpoint detection without color indicators or reference electrodes
• Continuous operation in non-conductive or turbid media with low maintenance
• Fast analysis times (often under five minutes) across diverse chemistries
• High precision for industrial quality control and process monitoring

Future trends and potential applications

Advances may include:

• Integration with miniaturized and microfluidic titration platforms
• Enhanced digital filtering and machine-learning algorithms for endpoint prediction
• Expanded non-aqueous and complex matrix analyses
• Development of novel catalytic endpoint reactions for ultra-trace determination

Conclusion

Thermometric titrimetry is a versatile and robust analytical technique that exploits reaction enthalpy for endpoint detection. Its adaptability to automated systems and wide applicability make it a powerful tool for modern analytical laboratories seeking speed, precision and objectivity.

References

• Brown MW, Issa K, Sinclair G Precise manual enthalpimetric titrations Analyst 94 234–235 1969
• Chen J, Fritz JS Gas chromatographic determination of water after reaction with triethyl orthoformate Anal Chem 63 2016–2020 1991
• Richter W, Tinner U Practical aspects of modern titration Metrohm Monograph 8.016.5003 2001
• VanDalen E, Ward LG Thermometric titration of hydroxide and alumina in Bayer process solutions Anal Chem 45 2248–2251 1973
• Carneiro MJD et al Determination of acidity of oils using paraformaldehyde as a thermometric endpoint indicator J Braz Chem Soc 13 692–694 2002
• Smith TK Analysis of FFA in edible oils by catalyzed endpoint thermometric titrimetry JAOCS 80 21–24 2003