Abstract: Via several techniques to modify sensitive matrix for inhabiting the leakage of fluorescent indicator, a new stable sensing material for monitoring phosphates has been prepared and applied to the measurement of phosphates in artificial seawater. It is based on the reaction of PO₄^3- with Al(Ⅲ)-Morin that leads to the fluorescence quenching of the composite matrix. At pH value 4.0 and the salinity value 25.0, the response time of output signal having reached the steady state is less than 300 seconds. Its calibration graph is gained in the range of H₂PO₄^- mass concentration from 1.50 to 7.00 μg/mL with the limit of detection(3σ/K) 0.02 μg/mL. When it was used to measure phosphates in artificial seawater, the recovery ranged from 96.78% to 102.09%. Being stored under the proper condition, the membranes maintain sensitive for 90-120 days, and are able to be used for 50-80 times with indicator supplement.

Key words: PVA/PVC composite membrane, Phosphate, Al-Morin