Design And Application Of Strong Acid Concentration Indicator Electrode

Acidity is an important physical and chemical parameter for evaluating the properties of a solution,in many fields including industrial production,scientific research,medical,food,etc.,acidity is an indispensable monitoring indicator.In some special production processes,high acidity medium conditions are often required,but at present there is no mature commercial high acidity testing instruments.In this paper,the design and application of strong acid concentration indicator electrode has been studied.（O-aminophenol-o-phenylenediamine）copolymer is synthesized by chemical oxidative polymerization,using the copolymer as a selective reagent,a PVC film electrode with a recognizable response to strong acid concentration is prepared,and a new method for the determination of strong acid concentration is established by potential analysis.In addition,a insoluble P₂W₁₈heteropoly which has been solidified by tetrabutylammonium bromide is used as a modifier to prepare a strong acid concentration electrochemical sensor.Based on this sensor,a new method for detecting strong acid concentration was established by cyclic voltammetry.This paper mainly carries out the following researches:（1）Using o-aminophenol and o-phenylenediamine as polymer precursors,and ammonium persulfate as initiator,refluxing in neutral medium at 100℃for 8 h,（o-aminophenol-o-phenylenediamine）copolymer is synthesized by chemical polymerization.There are 4 oligomers and 1 high polymer in the product are identified by thin layer chromatography,one of the oligomers is unstable and volatile.Four components are obtained by soxhlet extraction and column separation,and the structure of each component is studied by infrared spectroscopy.In order to determine the formation of the copolymer,poly（o-aminophenol）and poly（o-phenylenediamine）are synthesized under the same synthesis conditions with a single o-aminophenol or o-phenylenediamine as precursors.The formation of copolymer is confirmed by comparison of the differences in thin layer chromatography,infrared spectrum and ultraviolet spectrum between copolymer and smonomers.（2）A strong acid concentration indicator electrode is prepared with（o-aminophenol-o-phenylenediamine）copolymer as acidity selection reagents,and PVC as a film-forming agent.In order to find the best selective reagent,poly-o-aminophenol and poly-o-phenylenediamine film electrodes are separately prepared using the same method.The potential responses of three electrodes to concentration of 1.00～10.0 mol/L HCl and H₂SO₄are studied by potential analysis,finally the（o-aminophenol-o-phenylenediamine）copolymer is identified as the best acid-sensitive modification material.This electrode has excellent performance in aspects of wider response range and good stability.The concentrations and potentials have linear relationship in the solutions of the concentration rang of 1.00～7.00mol/L HCl or 1.00～10.00 mol/L H₂SO₄,and the linear regression equations are E（m V）=21.3c _HCl（mol/L）-88.4（r=0.999）and E（m V）=32.3c _H2SO4（mol/L）-105（r=0.999）respectively,and the linear relationship can remain unchanged within 180 days.In addition,the experimental results show that common ions do not interfere with the determination of acid concentration in high acidity environments.The method is applied to monitor of acidity in simulate production process of rare earth ion extraction,the relative error of the average value is-1%（n=5）,and the relative standard deviation is 2%.This electrode is simple to prepare,easy to use,and has a fast response time from 5 to 10 s,which will lay the foundation for real-time and online monitoring of strong acid concentration.（3）A insoluble ionic associate TBAB-P₂W₁₈heteropoly salt is synthesized by reacting tetrabutylammonium bromide（TBAB）with（NH₄）₆P₂W₁₈O₆₂,and the target of P₂W₁₈heteropoly acid curing has been achieved.A carbon paste electrode(TBAB-P₂W₁₈CPE)is prepared by mixing carbon powder and TBAB-P₂W₁₈which as a selective reagent for determination of strong acid concentration.And using TBAB-P₂W₁₈CPE as working electrode,the electrochemical behavior of TBAB-P₂W₁₈CPE in different concentrations of HCl,H₂SO₄,HNO₃and HCl O₄is studied by cyclic voltammetry,the results show:the reductive peak potential of the cyclic voltammetry curve is linearly related to the concentration of the same kind of acid,for 1.00～12.0 mol/L HCl solution,the linear regression equation is E_pc2=0.0164c（H⁺）-0.414（r=0.998）,and based on this,a new detection method for concentration of HCl is established.The method also has a good linear response to H₂SO₄solution with a concentration of 1.00～12.0 mol/L and HCl O₄solution with a concentration of 1.00～7.00mol/L.Common rare earth metal ions hardly interfere with the method,and the method is applied to the determination of the acid concentration in the simulated solution of rare earth extraction,and the relative standard deviation is 3%,and the accuracy is good.