Gout is a metabolic disease characterized by recurrent attacks of inflammatory arthritis. It is mostly connected with the state of abnormally high blood level of uric acid called hyperuricemia, which is considered to be the main cause of gout. The percentage of the population diagnosed with this disease is quite small, but the incidence of gout tends to grow nowadays. If non-pharmacological measures are not effective in controlling the disease, drug administration is needed. Although there are a few pharmacological groups of drugs that can be used in gout treatment, the main role is played by drugs that lower the blood concentration of uric acid. Allopurinol represents the first line of treatment, but in the case of its ineffectiveness or intolerance, febuxostat can be used. Febuxostat is a relatively new drug, which acts like selective, non-purine xanthine oxidase inhibitor. Xanthine oxidase is an enzyme that catalyzes the production of uric acid, therefore, its inhibition may help prevent and reduce the frequency of acute gout attacks. Febuxostat still does not have an official monograph in pharmacopoeia so it is highly necessary to develop fast, selective, sensitive and accurate analytical methods for the identification and determination of febuxostat and its impurities in active pharmaceutical ingredients and finished drug products. The aim of this diploma thesis was to analyze impurities in febuxostat. In order do to so, highly sophisticated HPLC-DAD-MSn method was used to separate febuxostat and its three impurities (febuxostat amide, febuxostat DEE, ethyl-febuxostat). Then, fragmentation pathways for all analytes were determined using mass spectrometry. Suggested pathways of fragmentation can be helpful in understanding the impurity profile of febuxostat, and can also contribute to a fast and easy way of impurity profiling of finished drug product. Hence, the sample of febuxostat extracted from a tablet was taken and analyzed. Many chromatographic peaks that matched impurities were noticed. Two out of three impurities of interest were detected in this sample, while the presence of the third impurity could not be confirmed with certainty. Also, four more peaks were noticed but they will be structuraly characterized and identified in later research.