A GPCL detection system is developed for the determination of inorganic selenium in water samples. By using analytical technique in this figure, such as derivatization, UV/ S2O 8 2- decomposition, stopped-flow injection and cryotrapping, the system can separate and preconcentrate the analyte from the matrix, then produce GPCL as a result of ozonation. The method was simple, sensitive with low-cost instrumentation.