The Evaluation of Optimal Conditions for Constructing of Potentiometric Gadolinium Sensor using Experimental Design

In this study, the synthetic ligand of ortho-phenylenediamine (C22H22N4O4) was used as an ionophore in the design and manufacture of Gd(III) ion selective carbon paste electrode. The D-optimal Mixture Design was used to investigate the effects of independent parameters and their correlations, for evaluating and optimizing of the components of the Gd(III) carbon paste electrodes. The Design-Expert (Plackett-Burman Design) software package Minitab ver. 17.0 optimized the composition of the membrane percentage of the proposed sensor. The experimental design method reduces of number of experiments and saving time and cost. Also consider simultaneously effect of factors on optimal condition, study non-linear relations and the interactions between factors is possible. The optimal components of the membrane included graphite powder 60.00%, paraffin oil 30.00%, ionophore 8.00%, and multiwall carbon nanotubes 2.00 %. Ion selective electrode show the Nernst slope of 19.08 mV/decade at a concentration range of 1.0×10-2 to 1.0×1.0-7 mol L-1,
with the detection limit of 2.14±10-8 mol L-1. The desired electrode has a response time of less than 15 seconds and relatively good lifetime in the pH 5-9 range. It can also be used in potentiometric titration of Gd(III) by EDTA.