The aim of study was nicotinic acid, nicotinamide, methyl nicotinate and hexyl nicotinate. Thermogravimetric analysis and TLC combined with densitometry were used to assess the stability of nicotinic acid and its derivatives. Thermogravimetric analysis was performed with a Perkin Elmer thermogravimeter and heat from 25°C to 700 ^oC at 20 ^oC min-1. The chemical stability of nicotinic acid and its derivatives in ethanolic solutions stored for 2 years at 8oC were examined by TLC combined with densitometry. Based on thermogravimetric analysis, there was no total loss of nicotinic acid (remains at 5% level) and nicotinamide (remains at 4% level). However, the total loss of methyl nicotinate occurred at 149,5^oC, and hexyl nicotinate occurred at 392.2oC, respectively. The densitometric and spectrodensitometric analyses performed showed that methyl nicotinate and hexyl nicotinate undergo a chemical changes during the 2-years of storage in an ethanolic solutions at 8^oC Nicotinic acid and nicotinamide are more stable compounds in relation to methyl nicotinate and hexyl nicotinate.

Keywords: thermogravimetry, TLC, densitometry, stability, nicotinic acid derivatives.