Studies On Potentiomeric Membrane Sensors For Toluene Based On Molecularly Imprinted Polymers

With the rapid development of industry, environmental pollutions, especially forOrganic Pollutants, have attracted considerable attention. Every day large quantities ofwaste water are poured into rivers without being cleaned, which cause seriousenvironmental pollution. Benzene series especially benzene, toluene and paraxylene arewidely used as basic industrial chemicals and organic solvents, which have become aserious threat to environment and human health. Their toxicity, irrtation,carcinogenicity and special smell, which may cause uncomfortable reaction, threatenhuman’s health severely. Therefore, there is an ever growing demand for detectingorganic pollutants in water and air with a rapid, sensitive and accurate method.Electrochemistry is one of the fastest-growing fields in chemistry today, in terms ofboth basic and applied chemistry. Polymeric membrane ion-selective electrode havebeen widely applied in various domains such as environmental, clinical and industrialanalysis owning to its attractive features including ease of use, excellent selectivity,low cost and high reliability. In recent years, with the development oflow-detection-limit ion-selective electrode, much attention has been paid to theapplication of ion-selective electrode.As highly suitable ionophores, molecularly imprinted polymers (MIPs) have emergedas attractive, simple, and seemingly general materials for selectively binding a widerange of analytes with predetermined selectivity for target molecular, high affinity androbustness. MIPs are considered to be the iedal ionophores for the ion-selectiveelectrode in environmental analysis since they are highly stable and easy preparation.Unlike sensors based other transduction techniques, potentiometric sensors do notrequire the template molecules to diffuse through the electrode membranes forgeneration of membrane potentials, thus dramatically reducing the response time, andthere are no size restrictions on the template compound. However, this type of sensor has not been explored much, reports on benzene series detection with this type ofsensor are still rather rare. In this thesis, a new imprinting method of molecular withoutbonding sites has been developed, and the obtained polymers were used as ionophorefor determination of various environmental pollutions. The contents of this thesis are asfollows:1. Preparation of molecular imprinting polymers: a new imprinting method ofmolecular without bonding sites has been developed. Molecularly imprinted polymers(MIPs) for toluene are synthesized by precipitation polymerization using toluene asporogenic template, methacrylic acid as functional monomer and divinylbenzene ascrosslinker. The recognition abilities of the obtained MIP and control polymer havebeen investigated by the classical steady-state binding method. Experiments show thatthe imprinted polymer exhibits a much higher capacity than that of the control polymerfor binding to toluene. The maximum amount bound by the MIP is21.6mg/g. Theproposed MIP has been successfully applied to the enrichment of toluene in tap watersamples with recoveries ranging from92%to103%. This methodology makes a newpathway for the preparation of small molecular imprinting polymers.2. Polymeric membrane ion-selective electrode for determination of toluene inwater: Toluene often exists as nuetral molecule in environmental water. However, todate it has been an open challenge for analytical chemists to develop potentiometricsensors for uncharged molecules, since the prerequisite for the general mechanism ofpotentiometric response is the occurrence of a charge on an analyte. In this thesis, wedescribe a novel strategy for selective and sensitive detection of neutral species using apolymeric membrane ISE, which is based on uniform-sized MIP as sensing element formolecular recognition and a charged compound with a structure similar to that ofanalyte as an indicator ion for transduction of potential signal. The membrane electrodeshows a liner dependence of the initial slope of the EMF change on the tolueneconcentration in the range of10~125μmol/L, and the detection limit is3.6μmol/L.The selectivity for paraxylene，naphthalene and ethyl acetate of the electrode has been characterized. The sensor shows good reproducibility, rapid response and long termstability.3. Polymeric membrane ion-selective electrode for determination of toluene vapor:benzene series are the most important composition of VOCs. However, there is no studyon determination of toluene in air has been reported with potentiometric sensor. Basedon the achievement in the development of ISEs based on asymmetric polymericmembranes for potentiometric trace-level detection of heavy metal ions, polymericmembrane ion-selective electrode using MIP as ionophore exhibiting high selectivityand rebinding capacity and excellent site accessibility to target species for determinationof toluene vapor is described in our present work. It is based on a molecularly imprintedpolymer (MIP) as an ionophore for molecular recognition, which can be synthesized byprecipitation polymerization using toluene as a template molecule and solvent,methylmethacrylate as functional monomers, and divinylbenzene as cross-linkers.Benzoic acid was used as an indicator ion to indicate the potential response changes.The enrichment ability to toluene vapor of ISEs was improved by optimizing themembrane component. The membrane electrode shows a liner dependence of the initialslope of the EMF change on the toluene concentration in the range of10~125μL/L,and the detection limit is3.3μL/L. The sensor shows good selectivity, rapid responseand long term stability.