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The aim of the master´s thesis was to verify the applicability of elemental analysis and molecular spectrometry for examining the authenticity of ketchup. For verify of share refractometric dry matter introduced into ketchup from tomatoes was used analysis of potassium and lycopene content. Ketchups with different tomato contents were prepared and subsequently models were created, which were used to verify the proportion of refractometric dry matter introduced into tomato ketchup in ketchups from the store. The results of the work showed that the amount of lycopene is a problematic marker for verifying the authenticity of ketchup, because during the production of ketchup, lycopene is degraded.In contrast, the amount of potassium in ketchup has been shown to be a good marker for monitoring the authenticity of ketchup. The model based on the potassium content of ketchup worked reliably, the deviations obtained from the quantity of tomatoes used for the production of ketchup indicated on the packaging were less than 10%. Higher deviations were achieved in ketchups with a minimum permitted tomato content of up to 20%. The concentration of potassium in ketchup with a lower content of used tomatoes can be significantly affected by the addition of other ingredients to the ketchup (onion, garlic, carrot, apple, etc.). In addition to the ketchup production technology used, the ripeness of tomatoes also has a significant effect on the model for verifying the authenticity of ketchup.