Selective determination of nicotinic acid and nicotinamide using terbium(III) sensitised luminescence

This paper reports a rapid and selective method based on the reaction of formation of a luminescent chelate between terbium(UT) and nicotinic acid. The determination of nicotinamide is also possible by its previous conversion into nicotinic acid by an alkaline hydrolysis step. Stopped-flow mixing technique has been used in order to develop the corresponding equilibrium and kinetic methods, which allow analytical data to be obtained in only ca. 2 and 0.2 s, respectively. Calibration graphs are linear in the ranges 0.81-122 and 0.81-162 muM, for equilibrium and kinetic methods, respectively, and the detection limits are 0.27 and 0.24 muM, respectively. The relative standard deviation is close to 3%. Both methods have been applied to the determination of nicotinic acid and nicotinamide in food and pharmaceutical samples. The recoveries ranged from 91.5 to 106. (C) 2001 Elsevier Science B.V. All rights reserved.