Glossary

Physicochemical Properties

Physicochemical properties refer to the physical and chemical characteristics of a substance that define its behavior under different conditions. These properties result from the molecular structure and composition of the substance and are fundamental in determining its interactions, stability, and functionality in various applications. In the context of materials science, pharmaceuticals, chemistry, and many other fields, analyzing and understanding physicochemical properties is crucial for the prediction of performance, processing and suitability for the intended use.

• Physical properties can influence a substance’s form and texture, and how it responds to changes in temperature, pressure, and other environmental factors. These include characteristics such as melting point, boiling point, polymorphism, solubility, density, viscosity, and particle size.
• Chemical properties are related to a substance’s reactivity with other chemicals. They include properties like pH, chemical stability, oxidation-reduction potential, and the potential for chemical reactions like hydrolysis, polymerization, or degradation.
• Thermal properties include specific heat capacity, thermal conductivity, thermal expansion, and glass transition temperature. These properties determine how a substance absorbs and transfers heat, and how it expands or contracts with temperature changes.
• Mechanical properties are relevant in material science and engineering and include hardness, tensile strength, elasticity, and brittleness. These properties define how a material behaves under various forms of mechanical stress.

Assessment of the physicochemical properties of substances requires a combination of theoretical knowledge and analytical techniques such as Differential Scanning Calorimetry (DSC), Thermogravimetric Analysis (TGA), and Rheology.

Various standards and guidelines, depending on the field and application, regulate the assessment of physicochemical properties of materials. In material science and environmental studies, standards from organizations like ASTM International and ISO provide methodologies for testing and evaluating these properties. In the pharmaceutical industry, guidelines such as those from the International Council for Harmonisation (ICH), particularly ICH Q6A, outline the necessary studies for characterizing the physicochemical properties of drug substances; ICH Q2A (R2), meanwhile, provides guidance on the qualification of impurities in new drug substances. Methodologies and instrumentation to be used for the characterization of pharmaceutical substances are also described in the general chapters of different pharmacopoeias.

Table 1: Thermal analysis applied in physicochemical characterization