Niacin. II: Identification of isonicotinic acid in niacin by liquid chromatography with diode array detection

Isonicotinic acid impurity in bulk niacin was detected and identified by comparison with a reference material by liquid chromatography with a diode array detector. The niacin was dissolved in dilute hydrochloric acid and chromatographed on an amine column with a mobile phase of methanol and water acidified with formic acid. Isonicotinic acid has a relative retention time of 1.5 compared with niacin (nicotinic acid), and the wavelengths of maximum ultraviolet (UV) absorbance for isonicotinic acid and niacin are 270 and 260 nm, respectively. The amount of impurity found in the niacin sample was 0.3%. Twelve formulations, including sustained-release products, one bulk material, and the United States Pharmacopoeia (USP) reference standard were tested. The impurity was detected in only the bulk and USP reference material samples.