[Fluorometric determination of pyridine and its derivatives by flow injection analysis]

A method for the fluorometric determination of pyridine and its derivatives has been developed by flow injection analysis using hydrogen peroxide at high temperature. The reaction system consists of two pumps to deliver reagent and carrier stream, sample injector, reaction coil (0.5 mm ID x 15 m, 150 degrees C), cooling coil (0.5 mm ID x 3 m, 30 degrees C), and cooling coil (0.5 mm ID x 20 cm, 0 degrees C). The wavelengths of the fluorometric spectrophotometer were set at Ex 305-350 nm and Em 380-410 nm, the flow rate of each solution was 1.0 ml/min. The carrier stream was deionized water. The reaction solution containing 10 mmol/L hydrogen peroxide in 0.2 mol/L phosphate buffer (pH 6.0) gave the maximum fluorescence intensity for pyridine and its derivatives. Linear calibration curves were obtained from 5 ng up to 100 ng of pyridine and its derivatives. The coefficient of variations for 2.5 ng (n = 10) and 25 ng (n = 10) of isonicotinic acid, isoniazide and acetylisoniazide were 1.8% and 1.1%, 1.6% and 1.2%, 2.1% and 1.4%, respectively. The detection limit (S/N = 3) was 250 pg for isonicotinic acid, 500 pg for isoniazide, acetylisoniazide, nicotinamide, isonicotinamide, nicotinic acid, and 2.5 ng for pyridine, nicotine, 2--picoline, 2--picolinamide and picolinic acid. The carrier stream containing organic solvent (methanol, ethanol or acetonitrile) decreased the fluorescence intensity, but in the case of acetonitrile there was less decrease than methanol or ethanol. This method allowed the analysis of 30 samples/h.