The colours of charge-transfer complexes of methyl viologen: effects of donor, ionic strength and solvent

4-(2-Aminoethylamino)-N-(4-methoxyphenyl)-1,8-naphthalimide can be used as a fluorescent labeling reagent for carnitine. The excitation and emission maxima of this reagent were observed at 436 and 524 nm in acetonitrile, respectively and the reagent reacted smoothly with carnitine to afford the labeled product under mild conditions. The detection limit of carnitine by using this reagent was ca. 30 fmol.