o-Phenylendiamine can react wi th butyl diketone to produce 2 ,3-dimethyquinoxaline in acidic medium at 80℃ for 60 min. The compound has strong fluorescence. The optimal excitation wavelength is 365 nm, emission wavelength is 483 nm. In the presence of dodecyl benzene sulfonic acid sodium, the fluorescence intensity in-creased significantly. The concentration of o-phenylenediamine in the range of 10-2000 μg/L has a good linear re-lationshi...