Applications Of Polymeric Membrane Potentiometric Sensors In Detection Of Non-aqueous Media

As the most explored and developed electrochemical sensor,ion-selective electrodes（ISEs）have the advantages of low cost,fast analysis speed,wide linear range,and independence from chromaticity and turbidity.Therefore,it is widely used in many fields such as clinical diagnosis,environmental analysis and industrial testing.So far,these sensors have successfully detected more than 60 analytes,such as p H,electrolyte ions,heavy metals,nutrients and carbonates.Although most of its analytical samples are aqueous solutions,its use in non-aqueous media is often unavoidable,so far,it is unclear to what extent organic solvents can affect the performance of the electrodes.In this thesis,the effect of water-soluble organic solvent on the electrode and the mechanism of electrode destruction were studied,and the superhydrophilic chitosan/polyvinyl alcohol hydrogel was used as the protective layer of the electrode.An electrochemical sensor that can be used in organic solvents wa s constructed,and the performance of the electrode in various complex environments was tested,and good results were obtained.1.Influence and mechanism of organic solvents on polymeric membrane ISEsAs the application range of ISEs becomes more and more extensive,the application scenarios they face are also complex and diverse.The electrodes often come into contact with organic solvents during the process from production to use.For example,in the surface functionalization process of a Membrane ISE,organic solvents are usually used to dissolve"linkage reaction"reagents.In addition,the ISEs are commonly employed to monitor trace elements in the productions of beer,liquor,and in polymeric methanol to light olefins.Therefore,in this thesis,the calcium ISE(Ca²⁺-ISE)was used as a model to investigate the influences of four water-soluble organic solvents:ethanol,acetic acid,methanol,and acetonitrile on the Nernstian slope and selectivity coefficient changes.The effects of solvent polarity,soaking time,and film plasticizer on the sensing performance were also investigated.Experiments show that the aprotic solvent acetonitrile has the strongest destructive ability towards the sensing performance of the ISE in terms of Nernstian slope and selectivity coefficient.Moreover,the effect on the sensing performance depends on the polarities of the protic solvents,the immersion time and the polarity of the membrane plasticizer.2.A polymeric membrane potentiometric sensor for potential detection in organic phaseAccording to the research in the previous chapter,in order to achieve the application of this type of electrode in non-aqueous samples,the surface of the polymeric membrane ISE was modified with a hydrophilic hydrogel.A polymeric membrane calcium ISE was selected as a model sensor,and chitosan/polyvinyl alcohol-based hydrogel was modified onto the surface of the polymeric membrane.The experimental results show that the modification of the hydrogel layer has no obvious effect on the linear range and response slope of the sensor,but the ability of resisting organic solvent damage is significantly improved.After exposure to ethanol with a concentration of up to 50%for 7 days,the modified hydrogel Ca²⁺-ISE The analytic performance of these electrodes has been rarely changed.3.Application of hydrogel-based ISEs in wastewater containing organic solventsWhen the electrode is finally applied in real samples,there are lots of limiting factors which can affect the sensing performance of the ISEs,such as suspended solids,organic solvents,oil droplets,and microorganisms.In this thesis,through laboratory simulation and field tests,respectively,the comparison between the proposed electrode and the traditional laboratory large-scale instruments for detection of calcium in real samples was carried out.It can be seen that the results obtained by the hydrogel-modified electrode correspond well with those obtained by ICP-MS.