Study On Phosphate Detection Method Based On Metal Molybdenum Ion Selective Electrode

Phosphorus is one of the essential substances for biological growth,but enriched phosphorus will cause eutrophication of water and affect normal life and production.Therefore,total phosphorus has become one of the important quality indicators to measure water quality.Generally,organic and inorganic phosphorus in water are called total phosphorus.In environmental water quality monitoring,digestion and other means are often used to convert it into orthophosphate,and then other methods are used to measure phosphate to further determine the content of total phosphorus in water.In this paper,the mechanism and practical application of molybdenum-based phosphate ion selective electrode are further explored.The main contents are listed as follows:（1）Cyclic voltammetry combined with Energy Dispersive Spectromeeter and X-ray photoelectron spectroscopy were used to explore the reaction mechanism of molybdenum-based phosphate ion selective electrode.Experiments studies have shown that the electrode can measure phosphate only in alkaline condition,and the optimum pH is 11.MoO₃ can only be produced on the surface of molybdenum electrode under sufficient OH^-condition.The increase of MoO₃ content makes the response potential of phosphate ion remarkable.Because of the particularity of MoO₃ molecule structure,HPO₄^2-ion can be embedded in it,which leads to the change of local charge density,which is manifested by the change of response potential.The standard equation between the concentration of phosphate solution and the response potential can be established to further detect the concentration of phosphate in unknown water samples.（2）After the phosphate sample is completely digested by O₃/UV oxidation digestion technology,it is fed into the detection cell of the phosphate ion selective electrode.The response signal of the original battery formed by the tested water sample and the reference electrode of the working electrode is amplified by the amplifier,and collected by the data acquisition system into the host computer.According to Nernst equation,the distribution coefficient is used to establish the model.The concentration of phosphate ion in the measured water sample can be obtained,and the total phosphorus content in the water can be further measured.Through comparative analysis of data,the whole measurement system and electrochemical workstation measurement values are roughly the same,making the overall process more simple and efficient.（3）Uncertainty analysis was carried out for the detection scheme of phosphate with molybdenum electrodes.Through the calculation of influencing factors in the whole process and the analysis of experimental data,according to the evaluation results,the main reasons affecting the detection accuracy of the detection system were the configuration of standard solution and the accuracy of amplifier circuit.Experiments on four standard phosphate solutions with different concentrations show that the expanded uncertainty of the test results is small.Through the evaluation of uncertainty,the main factors affecting the accuracy of measurement results are found.By eliminating or reducing the influence of these factors,the overall detection system is optimized and improved.