The thesis describes the development of an analytical method for determination of elemental impurities in the active pharmaceutical ingredient fosamprenavir calcium. Elemental impurities in drug products may be of organic or inorganic origin and come from different sources, and may potentially endanger drug efficacy or affect the safety of use. This paper gives a detailed overview of the importance of controlling the presence of inorganic impurities and describes the benefits of using ICP-MS techniques in aligning with increasingly stringent pharmacopoeia requirements. For ease of mass spectrum, ICP-MS is a fast technique for automatic qualitative, semiquantitative or quantitative elemental analysis in various samples. The mass specrta obtained are simple because the peaks are made of single-charged ions, regardless of the complexity of the matrix. In ICP-MS compounds are atomized and ionized regardless of the chemical structure in which an element of interest is incorporated. The interferences are usually due to the formation of multiple charged ions, oxides or polyatomic isobaric interferences formed in the plasma, and an overview of the effects of polyatomic interference as well as the method of their removal (collagen gas utilization, selection of appropriate isotopes of the analyte) is given. Validation of the method is necessary to confirm that it is suitable for the intended purpose. This paper presents a description of the performance tests that are necessary to validate the method. During the multielement analysis, a false positive osmium response was obtained (the problem of formation of toxic osmium tetroxide in the oxidising medium at elevated temperature). The method for stabilization of osmium necessary for the development of a good method for its determination is described. The method for the determination of Ag, As, Au, Ba, Cd, Co, Cr, Cu, Hg, Ir, Li, Mo, Ni, Pb, Pd, Pt, Rh, Ru, Sb, Se, Sn, Tl V in fosamprenavir calcium and the ethod for determination of osmium in fosamprenavir calcium were developed. The main performance features for each (linearity, quantification limit, selectivity, accuracy, precision and robustness) were tested with the proposed eligibility criteria. It has been shown that each of the developed methods meets all the criteria for all tested performance features and the methods were validated.