HPLC ANALYSIS OF QUINOLINIC ACID, A NAD BIOSYNTHESIS INTERMEDIATE, AFTER FLUORESCENCE DERIVATIZATION IN AN AQUEOUS MATRIX

Quinolinic acid (a,3-pyridine dicarboxylic acid), a biological interme diate in nicotinamide adenine dinucleotide (NAD) biosynthesis in micro bes and mammals and a brain excitotoxin, is not fluorescent nor electr ochemically active and its detection sensitivity by UV absorption is c omparatively low. Quinolinic acid was successfully derivatized in wate r-based samples by monodansylcadaverine, a fluorescence tag, and analy sed by high-performance liquid chromatography (HPLC). No extraction pr ocedure was needed and quinolinic acid was activated by water-soluble carbodiimide and derivatized under mild conditions. As little as 3 pmo l (500 pg) of quinolinic acid in 5 mu l of artificial cerebrospinal fl uid sample volume could be derivatized and detected at a signal to noi se ratio of 3:1. Thus, detection on a mass; basis by HPLC after fluore scence derivatization is about 300 times as sensitive as direct determ ination of quinolinic acid by UV absorbance (500 pg vs 150 ng). A vari ety of activators, fluorescent tags and reaction solvents and conditio ns were tested but found to be less effective.