Application of Densitometry for the Evaluation of the Separation Effect of Nicotinic Acid Derivatives. Part I. Nicotinic Acid and its Amides

Abstract

Nicotinic acid (1) and its amides, namely nicotinamide (8), N‐methylnicotinamide (9) and N,N‐diethylnicotynamide (10) were investigated by NP‐TLC, and RP‐HPTLC. The R_F values were obtained from the densitometric analysis. The separation factors ΔR_F, R_F ^α and selectivity α were calculated from the R_F values. The resolution R_S values obtained by use of the chromatogram were verified by use of densitometric analysis. It was affirmed, that R_S values can be correctly marked exclusively on the basis of the densitograms. The R_S values larger than 1.5 calculated on the basis of the densitograms were obtained for the pair of compounds (10)/(9) and (8)/(1) on RP18WF₂₅₄ plates, and by use of methanol+water in a volume composition of 30:70, and dioxane+water in volume compositions of 20:80 and 10:90 as mobile phases. However, these conditions did not provide for the complete separation of N‐methylnicotinamide (9) from nicotinamide (8). Adsorption thin‐layer chromatography (NP‐TLC) in the system of a neutral aluminum oxide 60F₂₅₄ and acetone+n‐hexane mobile phase in a volume composition of 50:50 provided the optimum conditions for the separation of all the studied compounds.

Keywords:

• TLC
• Densitometry
• Separation parameters
• Nicotinic acid derivatives

Acknowledgment

This research was financed by the Ministry of Science and Information Society Technologies by resources reserved for science in the years 2005–2008 as research project No. 3 T09A 155 29.