Micellar liquid chromatographic determination of nicotinic acid and nicotinamide after precolumn Konig reaction derivatization

In the Konig reaction, the heterocyclic nitrogen of a pyridine derivative reacts with cyanogen bromide and is afterwards coupled with an arylamine to give a polymethine dye. In the previous work, this reaction was automated using a flow injection system, and in this study we have coupled this system to a chromatograph to determine nicotinic acid and nicotinamide, after precolumn derivatization, using the Konig reaction. First, we checked the micellar chromatography behavior of the polymethines using a C18 column, a flow of 1 mL min^-1 and detection at 440 nm. After modeling, the composition of the selected mobile phase was 150 mM sodium dodecyl sulfate (SDS)–6% (v/v) pentanol pH 3. In this mobile phase, the analysis time was below 17 min, the calibrations were lineal in the range 0.05 to 50 (mu)g mL^-1 with regression coefficients above 0.999, and intra- and inter-day imprecision were below 5%. The method developed here was applied to the determination of nicotinamide and nicotinic acid in pharmaceuticals, serum and urine samples and the amounts determined were similar to those obtained using a reference method.