Development And Application Of Two Rare Earth Ions' Novel Imprinted Electrochemical Sensors

Imprinted materials,which have the excellent selectivity and anti-interference,can provide the complementary sites for corresponding templates.Recently,the imprinted electrochemical sensors have being developing rapidly due to the combination with electrochemical sensors and imprinted materials'advantages.There are many reports about the imprinted electrochemical sensors,but existing methods are lack of selectivity and sensitivity.Furthermore,most of them are suffer from the difficulty in elution and the easy separation between base electrode and imprinted membrane.The rare earth elements have being used in industry and agriculture extensively.Unfortunately,the excessive presence of rare-earth elements is harmful to the health of human beings because they can accumulate in the human body and result in a series of diseases.So it is necessary to control the intake of rare earth elements as well as research a method for the simple,sensitive and selective determination them.Two rare earth ions(Ce³⁺and Eu³⁺)was selected as the template ions due to they have the direct electrochemical signal.For tha aim to improve the detection sensitivity of sensors,graphene,carbon nano tubes,poly-catehol and poly-dopamine was introduced as the modified materials.Finally,seven imprinted electrochemical sensors were fabricated via different methods,all of them hold high selectivity as well as sensitivity and can determination of Ce³⁺and Eu³⁺in some real samples and satisfactory results were obtained.The main study contents are listed below:Imprinted electrochemical sensors of Ce³⁺:1.After exploring the interaction between CeCl₃·7H₂O and the monomer allyl phenoxyacetate?APA?by ultraviolet spectroscopy,Ce?III?ion-imprinted polymer particles?IIPs?was synthesized by simple precipitation polymerization.In which CeCl₃·7H₂O acted as template,APA acted as monomer,Ethyleneglycoldimethacrylate?EGDMA?acted as cross-linking agent and 2,2'-azobisisobutyronitrile?AIBN?acted as initiator,respectively.Then IR,SEM and BET all were used to characterize this polymer followed by mixing it with graphite powder in the proportion of 1:4 and a certain amount of adhesive paraffin oil also be added to prepare the ion imprinted carbon paste electrode.Ce³⁺was detected directly by differential pulse adsorptive stripping voltammetry?DPASV?and its oxidation peak appeared at about 0.93 V.All parameters affecting the sensor's response were optimized and a calibration curve was plotted at a linear range of 1×10^-61.0×10^-5 mol L^-1 and 1×10^-52.0×10^-4 mol L^-11 with the detection limit of 1.5×10^-7 mol L^-1.The other rare earth ions have no obvious oxidation peaks near 0.93 V even though the concentration is 0.1 mol L^-1,and they have no interference with the determination of Ce³⁺even at a concentration 500 times higher than that of Ce³⁺.This sensor was successfully applied to determination of Ce³⁺in two catalyst sample solution with RSD?3.0%?n=5?and recoveries in the range of97.8¹03.6%at our optimal conditions.2.To develop a method for rapid,simple and sensitive detection of cerium in food samples,a novel electrochemical sensor named Ce?III?-IIM/rGO/GCE was fabricated via in situ polymerization of Ce?III?ion-imprinted membrane?IIM?on the surface of reduced graphene oxide?rGO?-modified glassy carbon electrode?GCE?using acryl amide?AM?as a functional monomer,ethylene glycol dimethacrylate?EGDMA?as a cross-linker and azobisisobutyronitrile?AIBN?as an initiator.The experimental parameters for preparation of Ce?III?-IIM/rGO/GCE were optimized,and DPASV was established for the determination of Ce?III?.The sensor showed a wide dynamic range of 4.0×10^-91.0×10^-4 mol L^-1,low detection limit of 5.0×10^-10 mol L^-1 and good selectivity towards Ce?III?,100-fold of other rare earth elements or 200-fold concentration of Zn²⁺,Ni²⁺,Fe³⁺,Co²⁺and Cu²⁺produce no interferences in determination of Ce?III?.The obtained sensor was successfully applied to directly detect cerium in some types of food without any extraction,the relative standard deviation?RSD?of less than 3.3%?n=5?and recoveries in the range of 93.9%¹03.6%.3.For the aim to detect Ce?III?in food with selectivity,sensitivity and speediness,aelectrochemicalsensor?Ce?III?-IIM/PC/GCE?wasconstructedby electropolymerization of a poly-catechol?PC?film on glassy carbon electrode?GCE?followed by modifying a Ce?III?ion-imprinted membrane?IIM?formed with electropolymerization using o-phenylenediamine as monomer.After that,a differential pulse adsorptive stripping voltammetry?DPASV?was developed for determination of Ce?III?by the obtained sensor.Under the optimal conditions,the sensor possesses good reproducibility and storage stability.Furthermore,it can be used directly for determination of Ce?III?in the concentration range of 3.0×10^-12?1.0×10^-4 mol L^-1 with the limit of detection of 1.0×10^-12 mol L^-1.Since over 50-fold excess concentration of Fe³⁺,Cu²⁺and Ni²⁺will interfere with the detection of Ce³⁺,and there is more Fe³⁺in food.In order to apply this sensor to detect Ce³⁺in food samples,and considering that other rare earth ions do not interfere with the detection of Ce³⁺,we extract the rare earth ions by the extractant 1-phenyl-3-methyl-4-benzoyl-5-pyrazolone?PMBP?.After that,Ce?III?can be determined by Ce?III?-IIM/PC/GCE in the presence of more than500-fold excess concentration of Fe³⁺,Cu²⁺and Ni²⁺with the limit of detection of4.7×10^-9 mol L^-1.The sensor was successfully applied to determine cerium in food after extracted by PMBP with a relative standard deviation?RSD?of less than 3.3%?n=4?and recoveries in the range of 94.9?102.2%.Imprinted electrochemical sensors of Eu³⁺:1.For the aim to improve the sensitivity of detecting Eu³⁺,we use the dopamine as the modified materials considering that it has abundant hydroxide radical which may combine with the Eu³⁺.With the EuCl₃ as template,AM as monomer,EGDMA as cross linking agent,Fe₃O₄ as the carrier,we synthesized IIPs@Fe₃O₄ by surface imprinted polymerization which can improve the quantity of imprinted sites and reduce the equilibrium time.Then the carbon paste electrode was fabricated with the IIPs@Fe₃O₄and graphite powder in the mass ratio of 1:4.To improve the sensitivity of this sensor,dopamine was modified on the surface of electrode by electropolymerization.After optimized all of the detection conditions,the sensor was used to determination of Eu³⁺in aqueous phase with the linearity range and detection limitation were 3×10^-65×10^-4mol L^-11 and 4.0×10^-7 mol L^-1,respectively.We also study the detection equation and limitation of sensors without dopamine or IIPs,the linearity range of them was1×10^-55×10^-4 mol L^-11 and 3×10^-55×10^-4 mol L^-1,respectively.The detection limits of them both were 1×10^-6 mol L^-1.The result showed that the sensor modified with dopamine and IIPs have the best performance.2.To solve the problem that the ion-imprinted membrane modified on glassy carbon electrode?GCE?usually easily falls off,a screen printed electrode?SPE?which has a relative rough surface than GCE,was selected as the base electrode for preparation of an ion-imprinted sensor for determination of Eu?III?.The sensor was obtained by modifying SPE successively with carboxylic multiwalled carbon nanotubes?MWCNs-COOH?as signal amplifying element and Eu?III?ion-imprinted membrane?Eu?III?-IIM?as specific recognition material.To avoid damaging SPE by thermal initiation,the Eu?III?-IIM was prepared via radical photopolymerization at 380 nm using azobisisobutyronitrile?AIBN?as initiator.Differential pulse adsorptive stripping voltammetry?DPASV?was used for determination of Eu³⁺by the obtained sensor.After the detection condition was optimized in detail,the sensor showed a linear response to Eu³⁺in the concentration range of 1.0×10^-71.0×10^-3 mol L^-1 with the detection limit of4.0×10^-88 mol L^-1.The obtained sensor possesses of good regeneration,stability and practicability,it can maintain more than 95%of its original response after used more than 30 times or stored in the water for two months.The satisfactory results with the relative standard deviation?RSD?of less than 3.5%?n=5?were obtained for the determination of europium in water samples by the novel sensor.3.Catechol were firstly modified on the glassy carbon electrode by CV?PC/GCE?,then the IIM was fabricated on PC/GCE by electropolymerization with the Eu³⁺as template o-aminophenol?o-AP?as the monomer,respectively.After optimized all the detection conditions in detail,the designed modified electrode showed a linear response to Eu³⁺ions in the range of 3.0×10^-71.0×10^-4 mol L^-1 with the detection limit of1.0×10^-7 mol L^-1.The linear equation is logI??A?=0.6402×logC(?mol L^-1)–0.0573?r=0.9999?.And it possessed of good regeneration,stability and practicability.When the sensor was used to detect real water samples,satisfactory results were obtained.4.To obtain a sensor for the determination of Eu³⁺with excellent sensitivity,high selectivity and good stability,a screen printed electrode?SPE?was successively modified with poly catechol as signal amplifying element and Eu?III?ion-imprinted membrane fabricated by sol-gel method as the recognition material.After the factors influenced the sensitivity of the sensor for Eu³⁺was optimized in detail,Eu³⁺can be determined by differential pulse adsorptive stripping voltammetry?DPASV?in the concentration range of 3.0×10^-71.0×10^-33 mol L^-1 with the detection limit of 1.0×10^-7mol L^-1.The fabricated sensor owns outstanding selectivity,perfect stability and good regeneration.50-fold excess concentration of rare earth ions such as Ce³⁺,Tb³⁺,Ho³⁺,Dy³⁺,Er³⁺,Gd³⁺,Pr³⁺,Nd³⁺,Yb³⁺and 100-fold excess concentration of other metal ions such as Fe³⁺,Ni³⁺,Cu²⁺,Zn²⁺and Co²⁺have no influence on the determination of1.0×10^-55 mol L^-1 Eu³⁺.The obtained sensor,which can maintain more than 90%of its original response after used more than 60 times or stored in the water for two months,has been satisfactorily used to detect Eu³⁺in water samples with the relative standard deviation?RSD?of less than 3.6%?n=5?and recoveries in the range of 97.6%?101.6%.