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

Abstract

Nicotinic acid (1) and its derivatives, namely nicotinamide (8), 3‐pyridinecarbaldehyde (11), 3‐pyridinecarbonitrile (12), 3‐pyridylmethanol (13), and methyl 3‐pirydyl ketone (14) 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 comparison and characteristic of chromatographic bands of the examined compounds were presented on the basis of calculated resolutions: R_S(c), R_S(b), R_S(h), and R_S(a). The resolutions of substances were determined by visual method (R_S(c)) and densitometric method (R_S(b), R_S(h), and R_S(a)). It was affirmed that the densitometric method is correct and the standard method to determine the above mentioned parameters. Furthermore, the R _S parameter determined by the visual method for two adjacent substances is always larger than determined by the densitometric method. It was affirmed, that the best separation of the studied compounds was obtained by the RP‐HPTLC technique on RP18WF₂₅₄ plates, and by use of dioxane‐water in a volume composition of 20∶80. However, 3‐pyridinecarbaldehyde (11) from 3‐pryridinecarbonitrile (12) cannot be separated by the RP‐HPTLC technique. It was also affirmed, that adsorption thin‐layer chromatography (NP‐TLC) in the system of a silica gel 60F₂₅₄ and the acetone‐n‐hexane mobile phase in a volume composition of 80∶20 provided the optimum conditions for the complete separation of 3‐pyridinecarbaldehyde (11) from 3‐pryridinecarbonitrile (12).

Keywords:

• NP‐TLC, RP‐HPTLC
• Densitometry
• Separation parameters
• Nicotinic acid
• Nicotinic acid derivatives

Acknowledgment

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