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The Application of Schiff Base-metal Complexes in Ion-selective Electrodes

Author: ZhangMin
Tutor: ChaiYaQin
School: Southwestern University
Course: Inorganic Chemistry
Keywords: Ion-selective electrode Potentiometry Schiff base organometallic compound Salicylate ion Thiocyanate ion
CLC: O641.4
Type: Master's thesis
Year: 2008
Downloads: 129
Quote: 0
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Abstract


Ion-selective electrode (ISE) is a kind of indication electrode, the electrochemistry active element is a sensitive membrane which decides the potentiometric response characteristics. Organic compounds or organometallic compounds which has the possibility of recognited some cationic or anionic species act as ionophores that incorporated ion-selective poly(vinyl chloride) membrane electrode to expend the applications of ion-selective electrodes(ISEs), it is one of the most important of the research area of the potentiometric methods of the electroanalysis and of the organic or organometallic chemistry. The application of organometallic compounds as the sensitive materials of electrode membrane, which is take advantage of the electrochemistry characteristics, is a significantly absorbing research field of analytical chemistry, especially the electrochemistry sensor field between the last of twenty century and the first of twenty-one century.On one hand, the article simply present the performances and properties of Schiff base organometallic compounds, their basic conditions which are used as ion-selective electrode ionophore: lipophilicity, suitable mobility、fromation constant, adequate reaction speed, and the development of Schiff base organometallic compounds used as ionophore. On the other hand, this paper simply looks back the achievements of ion-selective elecetrode during the last ten years: excellent selectivity and low detection limit, and a series of analytical detection methods which derive from them, and several important development periods of ion-selective electrode as an analytical tool: the periods of the theory preparation, the design of electrode, the development and practical application, the research of new wave after lower interesting. In addition, two different organometallic compounds are designed and applied into PVC solvent polymembrane ion-selective electrode as ionophore. The response mechanisms were studied by UV-visible spectroscopy and EIS technology. The selectively, and the selectivity coefficients for interfering ions, linear range and detection limit were determined.1. An organometallic compound that copper (Ⅱ) 4,4’-bis (salicylideneimino) diphenylmethane was synthesized as a neutral ionophore for the preparation for polyvinyl chloride (PVC) membrane electrode. Based on orthogonal experiments, the composition of membrane was optimized because of the effect of membrane composition on electrode’s potentiometric response characteristics. The use of plasticizer di-(2-ethyl hexyl) phthalate and ion-addictive tridodecylmethylammonium chloride (TDDMAC(?)) improved the linear range and sensitively, respectively. Hence, the best membrane composition was (m%): m(Cu2L2) : m (PVC) : m (DOP) : m (TOMAC(?)) = 5.7:31.0:61.3:2.0. The electrode had excellent Nernst potential response for salicylate ion in pH range 4.0 - 8.5 with a slope of 55.3 mV/dec. It showed an anti-Hofmeister selectively pattern within the salicylate concentration of 2.7×10-5-1.0×10-1 mol/L with the detection limit 9.4×10-6 mol/L. The selectivity coefficient of Salfor interfering ions were determined by the separate solution method, and the selectivity sequence was Sal-> ClO4- > SCN- > I- > NO2- > NO3- > Cl-> Br- > SO32- > SO42- > H2PO4-, which was opposite with the classic Hofmeister selectivity sequence:ClO4-> SCN- > I-≈Sal- >NO3- > Br- > NO2- > Cl- > SO42- , named the anti-Hofmeister selectivity sequence. It was caused by the constituent of the ligand and the coreaction of centre metal atom with ion. In addition, the electrode had excellent potentiometric selectivity, stability and reproducibility. The response mechanism to the electrodes was described based on UV-visible absorption spectra and AC impedance technology. The electrode can be primary applied to analyses of medicine and the results obtained are in fair agreement with the results given by a titrimetry method.2. A novel PVC membrane ion-selective electrode is prepared with a new synthesized three nuclear dual-Schiff base metal nickel complex which is used as neutral ionophore. The use of plasticizer o-nitrophenyl octyl ether(o-NPOE) and ion-addictive four-phenyl-as sodium boron improved the linear range and sensitively, respectively. The optimized composition of electrode was m(Ionophore): m (PVC) : m (o-NPOE): m (NaTPB) = 5.5 : 30.0 : 62.1 : 2.3. The electrode exhibited Nernst response for thiocyanate ion with a slope of 57.5 mV/dec at pH range 2.0 - 8.0. It showed an anti-Hofmeister selectively pattern because the special characteristic of thiocyanate ion that thiocyanate ion prior to coordinate with centre metal atom. The selectivity sequence was SCN- > Sal- > I- > phCOO- > ClO4- > Cl- > Br- > NO3- > NO2- > Citrate > CH3COO- > SO42-. The electrode was able to detect thiocyanate ion within the thiocyanate ion concentration of 2.4×10-7-1.0×10-1 mol/L, and the detection limit 2.0×10-7 mol / L. In addition, the electrode has good selectivity, stability and reproducibility of life up to 45 days. The UV-Vis, AC impedance are used to research the response mechanism of the proposed electrode. In addition, the recovery is between 98.6% and 101.4% when the electrode is used for thiocyanate detection in wastewater

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