A new spectrofluorimetric microdetermination of nitrite in water after derivatization with 4-methyl-7-aminocoumarin

A method for analysing traces of nitrites is described. The method is based on the diazotization of a heteroaromatic primary amine-4-methyl-7-aminocoumarin (Coumarin 120((R)))-by nitrite ions in acidic medium. A large excess of Coumarin 120((R)) is mandatory for a quantitative reaction. The corresponding in-situ-produced diazonium salt is stable at room temperature and can be selectively isolated in the aqueous layer by extraction of the excess of unreacted Coumarin 120((R)) with ethyl acetate. The hydrolysis of the diazonium salt at 100 degrees C yields a fluorescent product, 4-methyl-7-hydroxycoumarin (4-methylumbelliferone), which is measured by direct spectrofluorimetry (lambda(ex) = 325 nm; lambda(em) = 380 nm). In this way levels of nitrites in water samples as low as 10 mug 1(-1) can be easily quantified.