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 ch romatography/mass spectrometry. The niacin bulk material was dissolved in pyridine and derivatized with N,O-bis(trimethylsilyl)trifluoroacet amide (BSTFA) reagent. The resulting trimethylsilyl (TMS) esters of ni acin and its associated impurities were chromatographed on a cross-lin ked methyl silicone capillary column with temperature programming. Der ivatization and injection of the 6 pyridinedicarboxylic acid geometric isomers showed that 3 of the dicarboxylic acids, 2,3- (also known as quinolinic acid), 2,5-, and 2,6-pyridinedicarboxylic acid, all rearran ge to give a component with a mass spectrum identical to that of the i mpurity. The other 3 isomers, 2,4-, 3,4-, and 3,5-pyridinecarboxylic a cid, do not rearrange, and therefore, cannot be the impurity detected in the niacin bulk material. The amount of pyridinedicarboxylic acid i mpurity in the bulk niacin is less than 0.02%.