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 Pharmacopeia (USP) reference standard were tested. The impurity was detected in only the bulk and USP reference material samples.

Gas Chromatographic/Mass Spectrometric Identification of a Pyridinedicarboxylic Acid Impurity in Niacin as the Trimethylsilyl Ester

A pyridinedicarboxylic acid impurity in bulk niacin was identified by derivatization and comparison with reference materials by using gas chromatogra-phy/mass spectrometry. The niacin bulk material was dissolved in pyridine and derivatized with N,O-bis(trimethylsilyl)trifluoroacetamide (BSTFA) reagent. The resulting trimethylsilyl (TMS) esters of niacin and its associated impurities were chromatographed on a cross-linked methyl silicone capillary column with temperature programming. Derivatization and injection of the 6 pyridinedicarboxylic acid geometric isomers showed that 3 of the dicar-boxylic acids, 2,3- (also known as quinolinic acid), 2,5-, and 2,6-pyridinedicarboxylic acid, all rearrange to give a component with a mass spectrum identical to that of the impurity. The other 3 isomers, 2,4-, 3,4-, and 3,5-pyridinecarboxylic acid, do not rearrange, and therefore, cannot be the impurity detected in the niacin bulk material. The amount of pyridinedicarboxylic acid impurity in the bulk niacin is less than 0.02%.