Development Of Miniaturized Ion-selective Electrode Detection Systems And Their Applications In Seawater Analysis For Calcium And Carbonate

The ocean is a complex system,and its chemical composition is continually changed by time and space.The changes in the seawater composition will have a large impact on the survival and growth of marine life.As one of the main components of seawater,calcium ions play an important role in the process of marine biological circulation and mineral formation.Therefore,the rapid detection of calcium ions in seawater is of great importance for monitoring the balance of marine ecosystems and understanding the growth and development of marine organisms.In addition,dissolved inorganic carbon is an important parameter of the oceanic CO₂ system,and carbonate is one of the species of dissolved inorganic carbons.The accurate detection of carbonate is important for understanding the global CO₂ cycle system and climate change.The conventional liquid-contact ion-selective electrodes?ISEs?are bulky and difficult to carry,due to the presence of the internal filling solutions.The solid-state ion-selective electrodes have been developed to overcome these shortcomings.However,the commonly used substrate materials as solid contacts are glassy carbon,gold and platinum,which are expensive and not suitable for mass production.Moreover,both the solid-state ion-selective indicator and reference electrodes are usually placed separately,which is not suitable for miniaturization of the device.In order to satisfy the point of care testing and on-site monitoring,ion-selective electrodes based on single-use,batch-production and inexpensive matrix materials have been developed.In this work,we have designed the screen-printed and paper-based ISE systems in which both the indicator and reference electrodes are involved for detection of Ca²⁺and CO₃^2-in seawater.The developed devices are simple,cheap and easy to prepare.The new systems are promising for seawater analysis.This thesis includes the following three parts:1.Screen-printed ion-selective electrode system for determination of Ca²⁺in seawaterThe screen-printing technology has been applied for preparation of miniaturized ISE systems.The carbon ink is commonly used as indicator electrode material,while the Ag/AgCl ink is employed for reference electrode.In order to improve the surface conductivity and electron transfer rate of the screen-printed carbon electrode,the electrode surface has been pretreated by the physical and electrochemical methods.The screen-printed calcium ion-selective electrode system has been developed by drop-casting the polymer calcium ion-sensitive membrane solution and the reference electrode membrane solution on the areas for the indicator and reference electrodes,respectively.The characteristics of the present electrode system have been investigated.Under the optimized conditions,the screen-printed Ca²⁺-ISE system shows a Nernstian response in a linear range of 1.0×10^-51.0×10^-11 M with a slope of 26.7±1.3 mV/dec.Additionally,the electrode system has been applied to the determination of calcium ions in seawater samples collected at various depths,and the results are in good agreement with those obtained by inductively coupled plasma optical emission spectrometry?ICP-OES?.2.Paper-based ion-selective electrode system for determination of Ca²⁺in seawaterIn recent years,paper has been used as a new type of electrode substrate material.Paper-based devices have advantages of low cost,easy miniaturization,simple posttreatment.In this work,paraffin ink-jet printing filter paper is uesd as the electrode substrate material to prepare a paper-based Ca²⁺-ISE system.The system includes a polymeric membrane solid-state calcium selective indicator electrode and a polymeric membrane reference electrode.The content of ionophore and the membrane thickness have been optimized.The stability of reference electrode and the selectivity of the ion-selective membrane have been investigated.The results show that the system shows a Nernstian response in the range of 1.0×10^-43.0×10^-22 M with a slope of 24.3±1.9 mV/dec in the presence of 0.5 M NaCl.The practical application of the paper-based Ca²⁺-ISE syetem has been carried out for determination of calcium ions in seawater samples.The results agree with those obtained by ICP-OES.3.Paper-based ion-selective electrode system for determination of CO₃^2-in seawaterFollowing the research of paper-based Ca²⁺-ISE syetem,we have chosen carbonate as the detection target,and used insulating tapes for further insulation and hydrophobic treatment of the electrode substrate to develop a paper-based CO₃^2--ISE system.We have investigated the characteristics of the electrode system in the artifical seawater?0.1 M Tris-HCl,pH 8?with a linear response of 4.4×10^-51.2×10^-33 M with a slope of 24.3±1.8 mV/dec.The electrode detection system has been used for the detection of seawater samples and the results agree with those obtained by the potentiometric titration method.