## 1 Introduction  
The biocompatibility and biodegradability, as well as the possibility of administering them in various dosage forms by multiple routes [1; 2; 3; 4; 5; 6; 7], make solid lipid microparticles (SLM) a promising carrier for many drug substances. Moreover, solid lipid microparticles, due to the combination of the active substance and the lipid in the SLM matrix, are being studied for various applications, such as prolonged action, taste masking, protection of the active substance or reducing irritation of the gastrointestinal tract. Lipid microspheres can be produced by various techniques, from simple and cheap one-stage processes to more complex ones requiring advanced equipment [7; 8]. SLM produced in the form of powder or liquid dispersion are often further processed into the final dosage form. The most common techniques for the preparation of SLM dispersions are the melt dispersion technique (also called the hot emulsification method), the solvent evaporation or diffusion method and the microchannel emulsification technique. Meanwhile, SLM in powder form can be produced by spray congealing, spray drying (from an organic solution) or cryogenic micronisation. The aqueous SLM dispersion can also be transformed into its dry form using the spray drying process or the lyophilization process [5; 9; 10]. Thermal analysis is a generic term used to describe analytical techniques that examine the behavior of a sample and the changes occurring in a material under the influence of temperature [11]. Different techniques are used, depending on the type of physical changes being analyzed when the sample is heated or cooled. The most popular methods for thermal analysis are differential scanning calorimetry (DSC) and thermogravimetry (TG). In the DSC method, the difference in the heat flux flow between the test substance and the reference material, as a function of temperature, is recorded. Meanwhile, in the TG method, the change in the mass of the sample is recorded as a function of temperature. The combination of both methods (DSC and TG) enables simultaneous thermal analysis (STA), the advantage of which is obtaining the comprehensive thermal characteristics of the tested sample [12]. In addition, in the case of simultaneous thermogravimetric analysis, both signals are recorded simultaneously on the same apparatus, and the prevailing conditions during the test (atmosphere, pressure, heating rate, the same measuring vessel, etc.) are identical for TG and DSC signals, which is important for the quality of the obtained results. This thermal analysis is a widely used method for studying not only pharmaceutical active substances and excipients, but also structured carriers and dosage forms. DSC and TG curves provide important information regarding the physical properties of various pharmaceutical compounds and formulations [11]. DSC is a powerful technique to determine the crystallinity of substances [13]. It is also used to test the physicochemical interactions of the drug and excipients and to exclude their potential incompatibilities [14]. It is known that both lipids and active substances are susceptible to polymorphic transitions induced by the production process (temperature changes, high shared forces, solvent evaporation and others) or occurring during storage [15]. These changes have a significant impact on the properties of the obtained drug form, such as the degree of incorporation of the drug substance into the lipid matrix, as well as on the stability of the dosage form (the risk of expulsion of the encapsulated drug from the lipid matrix) [15]. That is why it is so important to evaluate and control the properties of lipid microspheres using thermal analysis at various stages of the manufacturing process and during stability tests, as well as during quality control of the production batch. In this study the method of thermal analysis, including DSC and TG, was used to examine solid lipid microparticles in the form of liquid dispersion or fine powder.