The Study Of The Novel Detecting Instrument Based On Voltammetric Two-electrode System

Water is the source of life, it is the basic element of stable development of human society. The detection of water quality and property are more demanding than ever before. As a result, developing an advanced, reliable, quick, sensitive and cheap small size water quality detecting instrument is a hot topic in the related fields.The detecting instrument based on voltammetric technique has a good advantage in water quality testing and analysis. It has not only high sensitivity, simple structure and stable performance, but also own good flexibility. Various species can be detected by applying different potentials and alter different kinds of electrode. In this subject, on the basis of study of three-electrode system detection’s principle and conventional voltammetric detecting instruments, a two-electrode voltammetric detection system has been designed. In this system, a solid electrode with large surface area and stable electrode potential is acted as counter electrode and the glass reference electrode with inner solution commonly used in three-electrode system has been eliminated. In this study,a serious dxperiment such as the detection of pH value,Ca2+,Cr,H2O2,pb2+ions and caffeine in coffee solution has been carried out by using this two-electrode detecting system.The main study contents and results of this study include some following aspects:(1) On the basis of study of three-electrode system detecting principle and its instrument structure, the characterization of counter electrode in two-electrode system has been proposed, which is stable electrode potential, chemical inert, good conductivity, high mechanical strength, maintainance free and low costs. The two kinds of counter electrode:large surface area stainless steel electrode and active carbon electrode have been designed and fabricated and their characteristics have been studied.(2) A two-electrode system has been developed with a solid ion-selective working electrode and an active carbon counter electrode. pH value and Ca2+and Cl-ions in water can be selective detected via this two-electrode system by using pulse amperometric and cyclic voltammetric detection methods, respectively. The results indicated that, the relationship between the responses of the two detection methods and the testing ion concentrations are linear, with r>0.9970, RSD<1.05%. Comparing with potentiometric detection method, they are both free from charge accumulation interference which is promising in on-line monitoring applications.(3) A miniaturization voltammetric two-electrode detecting instrument has been developed which is composed by electrode probe unit, MCU control unit and software processing unit. MCU control unit has the function of working electrode changing, various potential output, and current responses collecting. Software processing unit has the function of working pattern selection, parameter setting, communication with MCU, current signal display, data analyze and processing, and results displaying according to the algorithm model, This detecting instrument has realized the detection process automation and intellectualization.(4) The application studies of this two-electrode voltammetric detecting instrument have been carried out. Hydrogen peroxide, lead ion and caffeine have been detected. In pulse amperometric hydrogen peroxide determination, the current response is linear with the concentration with r=0.9970, RSD<2.10%. In stripping voltammetric lead ion determination, the stripping peak current is linear with lead ion concentration with r=0.9996, detection limit of1.69ppb. The detecting results indicated that, the sensitivity, detection range and detection limit are all comparable with that of conventional three-electrode detection system. In order to expand the application areas of this two-electrode voltammetric detection system, it has been used in caffeine detection in coffee solution. Strong alkali type ion exchange resin pretreatment has been introduced to eliminated the interference species, enlarge the oxidation peak response of caffeine, increasing the detection sensitivity. The detection sensitivity of caffeine in pretreated coffee solution is44uA/g with r=0.9990.The research result shows that, by the use of the two-electrode voltammetric detecting instrument, combine with different detection methods and different electrode probe, various species such as pH value, mineral ions and micromolecules can be detected. This detecting instrument has high detection accuracy, good stabilization, simple structure, low cost, long lifespan, maintenance-free, easy tominiaturization, automation and intellectualization, which are turns out promising on water property monitoring in domestic applications.