A fluorescence carrier carbazole derivative 9-ethyl3-carbazylidene carbazole hydrazone(ECCH) with conjugated two carbazole ring has been synthesized.It can be fixed on the surface of optical fibre sensor to prepare a fluorescent sensor by PVC embedding method.When the solution pH value is 2.0

the reaction between nitrite(NO-2) and superfluous I-to form I3 which can quench the fluorescence of carbazole derivative and use in the sensor for the determination of NO-2.The quenching mechanism is discussed.The sensor shows sufficient repeatability

selectivity

operational lifetime.NO2 can be determined in the range from 1.0×10-6 to 1.0×10-4 mol·L-1 with a detection limit of 4.0×10-7 mol·L-1 at pH of 2.0.The recovery for the determination of ornidazole in water samples was ranging in 96.0%~103.6%