Studies On Novel Carrier Based Ion-Selective Electrodes And Molecular Imprinted Polymer Electrochemical Sensor

Ion-selective electrodes (ISEs) constructed by incorporating ion carriers into solvent polymetric membranes have been widely applied for the direct determination of several ionic species. Many of them showed potentiometric anion-selectivity sequences which differed from the Hofmeister pattern. The key components of the sensors are lipophilic complexing agents capable of reversibly binding ions. This thesis focuses on design and synthesis of several novel compounds and basic studies on solvent polymeric membrane ion-selective electrodes containing the compounds. The electrodes can be successfully applied to practice sample analysis. Recently, MIPs have drawn much attention because of their attractive advantages such as simple and economical preparation, predetermined selectivity and good recognition properties which are not affected by acid, base, heat or organic phase treatment. It is appropriate for MIPs to be used as the recognition components of chemical sensor. In this thesis, a conductometric chemical sensor based on salicylic acid imprinted polymer [P(SA)] has been described, which provides the possibility and basis of using the novel P(SA) based sensor for determination of the salicylic acid.Part I of the thesis deals with design of some novel carriers for poly(vinyl chloride) (PVC) membrane ion- electrode with high selectivity to Salicylate, Thiocyanate, Nitrite and Mercury( II) ion respectively.1. A novel poly(viny! chloride) membrane electrode with high selectivity toward salicylate(Sal) based on salicylal-imino acid Schiff base dibenyl complex of Sn(IV) [Sn(IV)-SIADBen] as ionophore was described. The influence on the electrode performances by lipophilic charged additives was studied. The results suggested that Sn(IV)-SIADBen acts onthe basis of a positively charged carrier mechanism. The influence of several other variables was investigated to optimize the potentiometric response and selectivity of the electrode. The electrode based on Sn(IV)-SIADBen, with 30.44 wt. % PVC, 64.55 wt. % plasticizer ( dioctyl phthalate, DOP ), 3.81 wt. % ionophore and 1.2 wt. % anionic additive exhibited a linear response for Sal" ion in concentration range 1.0x10"' to 2.5><10'6 mol I"1 and displayed anti-Hofmeister selectivity sequence as follows: Salicylate ? Perchlorate > Thiocyanate > Benzoate > Iodide > Nitrate > Chloride > Nitrite-Acetate > Citrate > Sulfate. UV-Visible absorption spectra was used to examine the specific interaction of salicylate with the ionophore. The e! ;ci; ;J ? was ?p '". ' in the clinic medicine analysis and the results obtained were consistent with those obtained by conventional method.2. A Novel salicylate-selective electrode based on an organotin complex with salicylal Schiff base of amino acid salicyladehydeaminoacid-di-n-butyl-Sn(IV)[Sn(IV)-SAADB] as ionophore is described, which exhibits high selectivity for salicylate over many other common anions with an anti-Hoi'meisier selectivity sequence: Sal" ? SCN' > PhCOO'> CIO4' > V > NO3" > NO2" > Br' > Cl" > CH3COO". The electrode based on Sn(IV)-SAADB, with 30.44 wt. % PVC, 65.45 wt. % plasticizer (diocty! phthalate, DOP), 3.81 wt. % ionophore and 0.3 wt. % anionic additive is linear in 6.0 x I0"6—1.0 x 10'1 mol I"1 with a detective limit of 2.0 x 10"6 mol I'1 and a slope of 62.0 ± 1.2 mV/decade of salicylate concentration in phosphate buffer solution of pH 5.5 at 25°C. The influence on the electrode performances by lipophilic charged additives was studied and the possible response mechanism is investigated by UV spectra. The electrode is applied to medicine analysis and the result obtained is satisfactory.3. A novel PVC membrane ion-selective electrode based on tribenzyltin(IV) dithiocarbamate [Sn(IV)-TBDTB] as neutral carrier was developed for thiocyanate (SCN") determination. The electrode exhibits a near-Nernstian response for SCN" with a slope of 62.2 ± 0.7 mV per decade over a wide concentration range l.Ox 10"1 ~ 2.Ox 10"6 mol I"1 and a detection limit of 9.2xlO"7mol I"1 in MES-NaOH buffer, pH 6.0, at 25°C. It shows a quite good selectivity for SCN" over a variety of other common anions and displays anti-Hofmeister selectivity sequence: SCN "> Sal " > I "> C1O4 ">Ac" >Br" > Cl" > NO3" > SO32" > SO42". The response mechanism is investigated via UV/Vis spectra and a.c. impedance technique which revealed that the excellent selectivity for thiocyanate was related to the unique interaction between the central tin(IV) ion and thiocyanate. The electrode has been used for direct determination of thiocyanate in wastewater with satisfactory results.