La(III) Ion Selective Electrode with PTFE Membrane Containing Tributyl Phosphate Ionophore

Abstract

Methods for the quantitative determination of lanthanum that have been developed are generally spectroscopic methods such as inductively coupled plasma mass spectrometry (ICP-MS), inductively coupled plasma atomic emission spectrometry (ICP-AES), and X-ray fluorescence spectrometry, which has relatively high operational costs. The feasibility of the potentiometric method using ion selective electrode (ISE) as an alternative method for lanthanum (III) determination needs to be studied because it is simple, easy to use, and has high sensitivity and selectivity. In this study, we developed ion selective electrode using PTFE membrane impregnated with tributyl phosphate (TBP) as ionophore. TBP is commonly used as a complexing agent for rare-earth ions in supported liquid membrane (SLM) separation process. We found that the compound can be used as an ionophore for ISE. This study aims to make a lanthanum ion selective electrode (III) (La-ISE) which has a Nernstian response. The parameters studied in the construction of this electrode were the effects of PTFE membrane immersion ionophore solution, ionic strength adjuster (ISA), and the inner solution composition. The performance parameters studied for the La-ISE were linear range, response time, detection limit, selectivity, and the lifetime of the electrode. Construction of the electrode begins with the preparation of the PTFE membrane as the main component. PTFE membrane was impregnated for 12 hours in the TBP solution having a concentration of 0.25 M or 0.50 M in kerosene. After it was dried, the membrane was attached to the end of the electrode tube with adhesive. Then, the electrode was filled with an internal solution containing a mixture of KCl 10-3 M with La (III) 10-3 M. The internal reference electrode was Ag/AgCl electrode. Before it was used, the electrode was soaked in a solution of La (III) 10-3 M for 12 hours.The effect of TBP concentration on the electrode performance was studied using two concentrations of TBP: 0.25 M and 0.50 M. The calibration curves obtained using both electrodes have good linearity. Nernst factor obtained from both electrodes is similar, although the Nernst factor obtained with an electrode having 0.50 M TBP closer to the theoretical value.ISA used in the measurement was KNO3. The effect of ISA on the performance of the electrode was studied using electrodes containing TBP with the concentration of 0.25 M or 0.50 M. The concentration of KNO3 used in this study was 0.01 M and 0.10 M. The Nernst factors obtained with electrodes containing 0.25 M TBP, in general, higher than those obtained with electrodes containing 0.50 M TBP in the same ISA. Electrode containing 0.50 M TBP resulted in the Nernst factor close to theoretical value when a measurement was conducted in 0.10 M KNO3.