Calcium Ion Selective Electrode Based on Schiff Base As Ionophore & Determination of Thermodynamic Functions & Its Analytical Application

A new, efficient Calcium ion selective electrode has been prepared using Schiff base based ionophore.The influence of temperature on electrode potential was studied & it can be used in the determination of thermodynamicfunction like DG, DH & DS.The electrochemical impedance spectroscopy(EIS)technique is also employed to study the electrochemical & surface reactions. It was also successfully used in the analysis of concentration of Calcium ion in various real samples. keywords: Calcium (II),Schiff base , Potentiometry, Electrochemical impedance spectroscopy.


INTRODUCTION
The introduction of new ion-selective electrodes has played a fundamental role in the development of various sensory elements according to the charge and size of the target ion in clinical and environmental assays [1][2][3][4][5][6][7][8] .Potentiometric methods using ISEs for determining the metal ion have been studied extensively due to their importance in biological process 9,10 , easy handling, nondestructive analysis and in expensive sample preparation, applicability to coloured sample and turbid solution.Calcium for mation of bone,neuro muscular function,coagulation&membrane permeability.In plants it helps in transpiration which leads to growth of the plant.Taking into consideration of all the above facts that a new simple ionophore such as Vinyl acetic acid grafted Pvc have been used as an electroactive phase for the fabrication of Ca 2+ ion selective electrodes .
In the present study the influence of temperature on electrode potential was studied & it can be used in the determination of thermodynamicfunction like DG, DH & DS.The electrochemical impedance spectroscopy(EIS) technique is also employed to study the electrochemical & surface reactions and the results are presented in this paper.

Synthesis of ionophore & Fabrication of the electrode
For preparing Schiff base ionophore ,1.1ml of Salicylaldehyde solution was mixed with 0.75g of glycine & the mixture was stirred. 11& this ionophore is used in the fabrication of the electrode.

Temperature study
The influence of the temperature on electrode potential was studied by standard procedure (Gurtu and Gurtu, 2011)) for the prepared electrode in different calcium ion concentrations at various temperature ranges from 5 -40°C.Because of the different temperatures, the ionic mobility of the ions which are to be analysed is different, so the potential was change.
Effect of temperature on electrode potential of the calcium ion selective electrode in the presence of aqueous, aquo-solvent and aqueous-buffer (pH) solution was used for the determination of thermodynamic functions like DG, DH and DS.
For the study of the effect of temperature on the output response, the temperature was changed in steps of 5°C.The values are tabulated in Table -1 The E.M.F.values of calcium ion selective electrode using the cell, Ca, Ca ionophore // Ag/AgCl was measured at different temperature ranging from 5 -40°C.The relationship between T(∂E/∂T)p and E of calcium ion selective electrode in different media was linear.
The relationship was linear in all the cases in accordance with the equation The value of temperature co-efficient (∂E/∂T)p in Table-1 in aqueous, aqueous -solvent, aqueous -buffer solution have been used in the calculation of DG, DH and DS at 5-40°C for the calcium ion selective electrode and the results were presented in the Table -2

Electrochemical Study
The impedance spectrum of the electrode was recorded at 10 mV amplitude in the frequency range of 0.01 to 1000 Hz.

CONCLUSION
A new simple ,highly specific&selective calcium ion electrode has been prepared.The life time of the prepared electrode was found to be 3 months with good reproducibility of E.M.F values.The thermodynamic parameter value DG, DH, DS of the electrode has successfully determined.macrocyclic polyether ligands composed of 1,10-phenanthroline as carriers for primary amine species," Talanta,1994, 41

Bedlechowicz
et al; 2002 developed calcium ion selective electrode using ETH1001 as an ionophore.In 2004 Kumar & Mittal developed a new calcium ion selective electrode based on PVC membrane modified by a new ionophore dibenzo-18-crown-6(DB18C6).All solid state miniature calcium ion selective electrode using Poly(3,4-ethylenedioxythiophene)doped with poly(styrenesulphonate)was carried out by Hui et al; 2013.All solid -state calcium ion selective electrode prepared of soluble electrically conducting polyaniline.(lindfors,Tand Ivaska, A,2000).

Table 2 :
Thermodynamic parameter values of ∆G, ∆H and ∆S