Calorimetric determination of dissolution enthalpy with a novel flow-through method

Area of Science:

• Physical Chemistry
• Materials Science
• Chemical Engineering

Background:

• Accurate determination of dissolution enthalpies is crucial for understanding solid-state properties and chemical processes.
• Traditional methods often require larger sample sizes, limiting analysis of microgram quantities.
• Developing microcalorimetric techniques is essential for high-throughput screening and polymorphism studies.

Purpose of the Study:

• To develop and validate a new calorimetric flow-through system for precise enthalpy of dissolution measurements.
• To assess the system's performance with small solid samples (<1 mg).
• To evaluate the system's accuracy and precision across different temperatures and substances.

Main Methods:

• A flow-through cell was designed as an add-on for a twin heat conduction calorimeter (TAM 2277).
• The system was tested using salts (NaCl, KCl), sucrose, and theophylline polymorphs in water at 25°C and 40°C.
• Standard electrical calibration and solvent preheating were employed to assess accuracy and mitigate heat leaks.

Main Results:

• The flow-through system demonstrated high accuracy and precision at 25°C for all tested substances.
• Precision was independent of the dissolution enthalpy magnitude.
• Results at 40°C were acceptable but slightly reduced due to heat leaks, which can be minimized by preheating the solvent.

Conclusions:

• The developed flow-through calorimetric system is effective for determining dissolution enthalpies of microgram-scale solid samples.
• Optimal performance is achieved at 25°C, with potential for improvement at higher temperatures by managing heat leaks.
• This system offers a valuable tool for precise solid-state characterization in various chemical and materials science applications.