Research And Development Of Phosphate Ion-selective Electrode Based On Molybdenum

Phosphorus as an important nutrients of aquatic organisms plays an important role in biological processes.However,high level of phosphorus content in water may cause excessive algae growth followed by eutrophication and degradation of water quality.With the development of economy,large amount of untreated industrial and agricultural sewage were directly discharged into the river.Thus the phosphorus content exceeded the standard content and resulted in water pollution,which even endangered the survival of plants and animals.Therefore,it has become a top priority for accurately monitoring concentration of phosphorus in the water and timely controlling content of phosphorus.Ion-selective electrode is selective,stable,simple,cost-effective,suitable for real-time measurement and gradually used to detect the concentration of phosphate in water.In this work,a novel phosphate sensor based on molybdenum was developed for aquatic sample analysis.The main contents are listed as follows:(1)A phosphate ion-selective electrode(ISE)based on molybdenum was developed,which is based on the reaction between molybdenum and hydrogen phosphate ions(HPO42-)in alkaline condition.The electrode showed a near Nernst characteristics with a slope of-26.9±0.5 mV/decade in Na2HPO4.Potential linear range is from 10-1 M to 10-5 M and detection limit is 1.9×10-6 M in the pH of 8.5.The response time is less than 50 s.The standard deviation of the response potential in the continuous measurement is 2mV.The standard deviation of the potential is less than 2mV in the reciprocating measurement of the different concentration of the solution to be measured.And in addition to the OH-measurement have a certain influence,the molybdenum electrode on the HPO42-have a good selectivity.The measurement data shows that the ISE can be used over a period of three months with good reproducibility and selectivity.The manufacture process of the ISE is easy and inexpensive.It can be applied to quantitative analysis of phosphate in water.(2)According to the influence of pH on distribution coefficient and molybdenum electrode's measuring potential,the distribution coefficient and pH linear compensation term were introduced into the Nernst equation so that the measurement model of the phosphate ion-selective electrode was established to overcome the influence of pH.The electrode showed a near Nernst characteristic with a slope of-24.32±0.5mV/decade from 10-1 M to 10-6M.The detection limit was 1.17×10-6 M and the electrode showed a good linear response.The performance of the phosphate ISE can be satisfactory for the measurement of phosphate ions and used for on-line monitoring of phosphorous content in the actual water.(3)In order to solve the shortcoming of the traditional online measurement technique of phosphorus concentration,such as complicated measurement,expensive equipment and extra reagents,the oxidation digestion technology based on UV/O3 and the phosphate ion-selective electrode based on molybdenum were used to measure the concentration of phosphate.And the measurement results were revised by establishing the measurement model.During the experiment,it was found that the digestion solution of oxidation digestion mainly showed acidity,which did not meet the requirement of alkaline measurement.The pH of the digestionsolution was needed to be adjusted by the electrolytic water.The experimental results showed that the pH adjustment had a great influence on the measurement of the electrode and the level of pH adjustment was depended on the actual measurement requirements.When the pH value of the digestion solution was higher than 7.5,the electrode showed a near Nernst characteristic with a slope of-26.092±0.5mV/decade from 2.68×10-6 M to 9.7×10-5 M and the detection limit was 2.68×10-6 M.When the level of pH adjustment was less than 7,the slope of electrode response was reduced to-24.622±0.5mV/decade,the linear range was widened to1.14×10-6 M to 1.01×10-4 M,and the detection limit was also decreased to 1.14×10-6 M.The pH adjustment was not inconsistent and the volume of the electrolytic water which added to the different concentrations of the digestion solution was different.Need to be determined by the solution's pH.