Abstract: It is of great importance to quickly determine the trace total iron in the water-steam system to figure out the corrosion status of the thermal system in a timely manner. Unfortunately the procedures of conventional method are too complicated and inconvenient to perform field testing. The flow injection analysis (FIA)-TPTZ spectrophotometry is proposed in this paper as a quicker and simpler way to determine the trace total iron in the water. In order to further improve this method to detect the trace total iron below the lower limit, the in-depth study is carried out on the major factors affecting the sensitivities, such as the reagent and carrier pump speeds, the colour coil length and the pH values of buffer solution and samples. After such improvements, in the range of 0.5~100 μg/L, the liner regression coefficient is now above 0.999, the RSD less than 1.0%, and the detection limit is extended down to 0.5 μg/L from previous 22.7 μg/L, with the detection rate at 60 samples per hour. The relative error is less than 10% in comparison with the current standard method. Therefore, it is suitable for automatic detection of trace iron and easy to be applied for on-line monitoring.

Key words: power plant, water-steam analysis, ppb level iron, FIA, spectrophotometry method, TPTZ