Studies On Anion-Selective Electrode With Organometallic Complexes As Neutral Carriers

Design, synthesis and application of highly selective and sensitive neutral carriers are main research subjects in the ion-selective electrode studies. Recently, study on ion-selective electrodes with anti-Hofmeister selectivity pattern is an important and interesting project in the fields of electrochemistry and electroanalytical chemistry. This thesis focuses on seeking design and synthesis of novel metallic complex and basic studies on solvent polymeric membrane (SPM) anion-selective electrodes containing the novel metallic complex. The electrodes can be applied to practice sample analysis.Part I of the thesis deals with design of neutral carrier for solvent polymeric membrane iodide electrode with high selectivity1. A new solvent polymeric membrane electrode based on chiral Schiff base-Co(II) complexes is first described which demonstrates excellent selectivity toward iodide ion. The bis(salicylaldehyde)R,R-1,2-cyclohexanediaminecobalt(II) [Co(II)Salcn], bis(salicylaldehyde)R,R-1,2-cyclohexanediaminecobalt(II) [R,R-(-)-Co(II)Salcn] and bis(salicylaldehyde)S,S-l ,2-cyclohexanediaminecobalt(II) [S,S-(+)-Co(II)Salcn] were synthesized for preparation of iodide ion selective electrode. The electrode based on [R,R-(-)-Co(II)Salcn] exhibits fairly low detection limits and potentiometric anion-selectivity sequences deviated from the Hofmeister pattern. The selective sequence is I- > NO2- > SCN- >C1O4- > Br- >NO3- > Cl- > SO42-. This electrode shows a near-Nernstian potentiometric response for 1 x10-1~7.0x 10-7 mol/L I- with a detection limit of 4.0x10-7 mol/L and a slope of-57.0 mV/pI in 0.01 mol/L H3PO4 buffer solution neutralized by NaOH to 2.5. The electrodes can be applied to medicine sample analysis with satisfactory results. The high potentiometric selectivity for iodide is thought to be related to (1) interaction between cobalt(II) complexes with iodide in acid solution and (2) chiral complexes with space effect. Oxygen could oxidize iodide ion to iodine in low pH aqueous solutions and the reaction transfer between central cobalt and the iodine in iodide complexes which could be described as Co3+...I-. The chiral complexes withsteric effect could improve electrode selectivity for I". The A.C. impedance spectra of electrode membranes incorporating ionophores have also been studied. The results obtained shows that chiral Schiff base complexes of Co(II) could uptake iodide across the membrane and the transfer process is diffusion controlled.2. A systematic study on about five Bis(l,3,4-thiadiazole) derivatives and 15 complexes based on mercury(II) salts showed that the complexes with more than four carbon chain were the most promising candidates for iodide ionophores. The sequence of selective response of the sensing membrane is r>ClO4->SCN->NO3->Br->Cl->Ac->SO42- deviated from the Hofmeister pattern. A new solvent polymeric membrane electrode based on bis(l,3,4-thiadiazole) complexes of Hg(II) is first described which demonstrates excellent sensitivity toward iodide ion. Some ionophores of a , w -bis(5-methyl-l,3,4-thiadiazole-2-yl-thio)-alkane with Hg(II) were synthesized for preparation of SPM electrodes with possibly improved detection limits. It turned out that among the complexes tested the one prepared with l,4-bis(5-methyl -l,3,4-thiadiazole-2-yl-thio) butane and mercury nitrate was the best iodide ion carriers. The PVC iodide electrode containing [Hg2(II)BMTB(NO3)4] shows a Nernstian potentiometric response for 2.0 x 10-8 to 2.0 x10-2 mol/L with a detection limit of 8.0x 10-9 mol/L and a slope of -59.0 mV/pI (25C) in 0.01 mol/L phosphate buffer solution (pH=3.0). The high potentiometric sensitivity for iodide is thought to be related to the unique interaction between mercury(II), the central cation of the complexes, and iodide in acid solution. The A.C. impedance spectra of electrode membranes incorporating ionophores have also been studied. The results obtained shows that complexes of Hg(II) could uptake iodide across the membrane and the transfer process is diffusion controlled. Iodide...