Fabrication And Characterization Of PVC Membrane Ion-Selective Electrode Based On Novel Complexes As Sensing Carriers

Potentiometry is a classical electrochemical analysis method. Direct potentiometry, one of the two potentiometry methods, is called ion-selective electrode (ISE) method, which carrys out the quantitative analysis by converting the live degree or concentration of ion into potential signal by using ion-selective electrode (i.e. membrane electrode). ISE is a sort of chemistry sensors also is a kind of indicator electrodes. The relationship between the potential value indicated by an ISE and the live degree of the corresponding ion is accordance with Nernst-equation. The essential of this method is to determine equilibrium potential indicated by the indicator electrode when the cell system is controlled under zero-current state, and further to calculate the concentration of the analyte ion according to Nernst-equation and the obtained potential value. A perfect ISE should be able to rapidly and steadily respond the analyte. Compared with other analysis methods, ISE method owns such many unique advantages as simple equipment, convenient operation, cheap cost, fast analysis, wide linear range, high sensitivity and etc. It's a fast analysis method developed rapidly in near years.The research key of ISE is to exploit, design and synthesize certain compound which can identify particularly a target analyte ion, and to use it as the sensing carrier of ISE. Immobiling the sensing carrier in polyvinyl chloride (PVC) matrix makes ISE be prepared easily, used conveniently and performed perfectly. Up to now, many sensor researchers started with electrode carrier, introduced successively novel compounds with especial function into PVC membranes and have constructed successfully many anion- and cation-selective PVC membrane electrode. At present, design and synthesis of many novel compounds, use them as the carriers of ISEs and establishing new measurement system for a target analyte are showing active situation. The researchers have been seeking all kinds of approaches and means to improve the potential response performance of ISE and the function and purpose of analysis system by ISE. In this work, according to the principle of selecting electrode carrier, metallophthalocyanine derivatives and Schiff bases with special structure and performance which can selectively interact with target anion or cation were synthesized and used as the sensing carriers of PVC membrane ISEs. As a result, certain anion- and cation-selective PVC membrane electrodes were fabricated successfully. Electrochemistry methods and means were used to characterize the potential performance of the resultant ISEs, and the new analysis system for a target analyte was established. The dissertation consists of primary section and secondary section:Primary section: Fabrication and characterization for PVC membrane anion ISEs.(一) An I^-selective PVC membrane electrode based on phthalocyaninatotitanium(â…£) oxide (PcTiO) complex was prepared successfully. The potential response of the electrode was optimized by changing the nature of plasticizers, the concentration of carrier, and ion additives. The basic electrochemistry characteristics investigated for the optimized membrane suggested that the resulting electrode to I^- showed selectively identifying process and good potential analysis performance in a linear range of 1.0×10^-1 - 9.2×10^-7 mol·L^-1 with a slope of -58.9 mV·dec^-1 and a detection limit of 8.5×10^-7 mol·L^-1. The selectivity sequence was: I^-＞SCN^-＞NO₂^-＞Br^-＞ClO₄^-＞C₂O₄^2-＞SO₃^2-＞F^-＞NO₃^-＞Ac^-＞Cl^-＞SO₄^2-＞H₂PO₄^-. The high sensitivity and selectivity showed by the proposed electrode to I^- may be originated from the reversible interaction between the central metal Ti(â…£) and I^- at axial direction. And the preferential potential response might be resulted from the effective process of I^- crossing the PVC membrane taken by the carrier PcTiO.(二) The potential response of PVC membrane electrodes based on metallophthalocyanines of Zn(â…¡) and Mn(â…¢) (ZnPc and MnPc) as carriers was investigated. The observations suggested that the electrode based on ZnPc showed selective near-Nernstian potential response to SCN in a linear range of 1.0×10^-1 - 1.0×10^-6mol·L^-1 with a slope of -58.1 mV·dec^-1 and a detection limit of 7.5×10^-7 mol·L^-1. The potential response difference between the electrode B without additive and the electrode G with cationic additive HTAB indicated that the presence of HTAB improved the senstivity, linear range and detection limit, but resulted in the decrease of the selectivity. The selectivity sequence for the electrode B was: SCN^-＞Sal^-＞I^-＞ClO₄^-＞Br^-＞Cl^-＞NO₃^-＞NO₂^-＞H₂PO₄^-＞SO₄^2-. The good potential response showed by ZnPc-based electrode to SCN^- may be originated from the reversible interaction between central metal Zn(â…¡) and SCN^-.(三) The potential response of the PVC membrane electrodes baed on two metallophthalocyaninederivatives, 2,9,16,23-copper(â…¡)-tetra-nitro phthalocyanine (CuTNPc) and 2,9,16,23-copper (â…¡)-tetra-amino phthalocyanine (CuTAPc) as carriers were studied. The result obtained indicated that the electrode based on CuTAPc with electron-repulsive showed sub-Nernstian potential response of to Sal^- with a slope of -49.5 mV·dec^-1. And the electrode incorporating CuTNPc with electron-withdrawing groups (NO₂) exhibited preferential selectivity and good potential response characteristics for Sal^- which may be suggested by that, in the presence of electron-withdrawing groups NO₂ in CuTNPc, the low electron density in the vicinity of central Cu(â…¡) atom was favorable for the coordination of Sal^-. The addition of anion additive NaTPB improved greatly the potential response characteristics and the selectivity. The resulting electrode gave a near-Nemstian solpe of -59.8 mV·dec^-1 with a linear range of 1.0×10^-1 - 9.0×10^-7 mol·L^-1 and a detection limit of 7.2×10^-7 mol·L^-1. Its selectivity sequence was: Sal^-＞SCN^-＞I^-＞ClO₄^-＞NO₃^-＞Br^-＞NO₂^-＞Benzoate＞Cl^-＞OAc^-＞SO₄^-2＞C₂O₄^-2＞Lactate＞Citrate, According to the theoretical models that predict the effects of ion sites on the selectivity, CuTNPc may act on the basis of a charged carrier mechanism.(å››) The potential response of a PVC membrane NO₂^- -selective electrode based on a aluminum(â…¢)-phthalcyanine (AlPc) as sensing carrier was investigated. The observations indicated that the electrode with the optimized membrane containing cationic additive TOMAC exhibited near-Nernstian linear response in five orders of magnitude with a slope of -58.3 mV·dec^-1 and a detection limit of 9.5×10^-7 mol·L^-1. The selectivity sequece obtained was: NO₂^-＞SCN^-＞Sal^-＞ClO₄^-＞I^-＞NO₃^-＞Cl^-＞OAc^-＞Br^-＞SO₄^2-＞H₂PO₄^-. But the addition of anionic additive NaTPB intensively deteriorated the potential response of the electrode.(五) The potential response of the PVC membrane electrodes based on three Schiff base metal complexes Cu(â…¡), Mn(â…¢) and Zn(â…¡) of N,N'-bis(salicylidene)-1,2-bis(p-aminophenoxy)-ethane (BBAP) (CuBBAP, MnBBAP and ZnBBAP) as carriers was investigated. The observation indicated that the electrode based on CuBBAP with sequare-planar structure displayed a preferential selectivity to I^-: I^-＞SaN^-＞ClO₄^-＞NO₂^-＞H₂PO₄^-＞NO₃^-＞SO₄^2-＞Br^-＞Cl^-. The electrode doped with the optimized membrane showed near-Nernstian linear response in a range of 1.0×10^-1 -8.2×10^-7mol·L^-1 with a slope of -58.8 mV·dec^-1 and a detection limit of 5.3×10^-7 mol·L^-1. But the electrodes based on MnBBAP with trigonal-bipyramidal and ZnBBAP with tetrahedral structure exhibited no good response behavior to I^-. The potential response difference between them may imply that the steric chemical environment has an important influence on their performance.Secondary section: Fabrication and characterization for PVC membrane cation ISEs.(一) The potential response of the PVC membrane electrodes based on simple Schiff bases, N,N'-bis(2-hydroxybenzyl)-1,3-diaminopropane(BHDP), N,N'-bis(2-hydroxybenzyl)-2,2-dimethyl-1,3-diaminopropane(BHDDP), and N,N'-bis(2-hydroxybenzyl)-1,4-diaminobutane(BHDB), as neutral carriers was discussed. The experiments observed indicated that the resulting electrodes based on BHDP and BHDB showed preferential selectivity recognition and stable near-Nernstian characteristics toward Ag⁺. The two electrodes gave respectively a slope of 58.7 and 58.1 mV·dec^-1 in five orders of magnitude with a detection limit of 1.0 umol·L^-1, and the selectivity sequence was: Ag⁺＞Cu²⁺＞Pb²⁺＞Co²⁺＞Hg²⁺＞Cr³⁺＞Al³⁺＞Mg²⁺K⁺＞Cd²⁺＞Zn²⁺＞Ba²⁺＞NH₄⁺＞Ca²⁺＞Mn²⁺＞Sr²⁺＞Bi³⁺ and Ag⁺＞Cu²⁺＞Pb²⁺＞Mg²⁺＞Hg²⁺＞Cr³⁺＞Al³⁺>K⁺＞Cd²⁺＞Zn²⁺＞Co²⁺＞Ba²⁺＞NH₄⁺＞Ca²⁺＞Mn²⁺＞Bi³⁺＞Sr²⁺, respectively. And relatively low sensitivity was observed for the electrode based on BHDDP with a slope of 53.7 mV·dec^-1. The difference between the electrodes may be attributed to the steric structure of BHDP and BHDB suitable for Ag⁺.(二) The potential response of the PVC membrane electrodes incorporating two Schiff bases(Lâ… and Lâ…¡) with N and O donor atoms as neutral carriers was investigated. The observations indicated that super-Nernstian potential response of 34.1 mV·dec^-1 slope for the electrode based on Lâ… to Pb²⁺was observed. But the resulting electrode based on Lâ…¡showed selective potential recognition and obvious near-Nernstian response to Pb²⁺ in Pb(NO₃)₂ solution or partially non-aqueous media, which gave a selectivity sequence of Pb²⁺＞Cd²⁺＞Mg²⁺＞Cr³⁺＞Al³⁺＞Hg²⁺＞Zn²⁺＞Co²⁺＞Ca²⁺＞Ba²⁺＞Cu²⁺＞NH₄⁺＞Ag⁺＞Bi³⁺K⁺ in a linear range of 1.0×10^-1- 1.7×10^-6 mol·L^-1 with a slope of 29.5 mV·dec^-1 and a detection limit of 1.0μmol·L^-1.