Through the extraction of soil sample in 0.5mol/L NaHCO 3,FIA is adopted to measure the density of PO 3- 4 in the extracting solution.According to that ethyl violet-ammonium molybate-OP complex coloring system react and generat the blue ternary ion complex,flow path of FIA is designed to make coloring and measuring completed on line.All technical parameters of this flow path have been experimented on in detail and have been optimized.The results show that:the blue ternary ion complex generated after reaction has the maximum absorption at the point of wavelength 430nm,with linear correlation coefficient 0.9997 and RSD less than 0.2%.Results obtained from measuring the actual sample have significant positive correlation with the proposed values.
