Negar Rajabi - Department of Chemistry, Mashhad Branch, Islamic Azad University, Mashhad, Iran
Mahboubeh Masrournia - Department of Chemistry, Mashhad Branch, Islamic Azad University, Mashhad, Iran
Mohamadreza Abedi - Department of Applied Chemistry, Quchan Branch, Islamic Azad University, Quchan, Iran

In this work, D-optimal mixture design was applied as an experimental design to screen and optimize the effect of the composition of a carbon paste on its performance. In this study, chitosan was offered as a ligand for the determination of La(III) with the carbon paste electrode. In the fabricated sensor, the greatest nernstian slope was achieved on the optimized mixture composition by experimental design: 60.00% w/w powder graphite, 1.53% w/w multi-walled carbon nanotubes (MWCNTs), 29.79% w/w paraffin oil, and 8.68% w/w chitosan. MWCNT was used for increasing the electrode response to La(III). The quadratic fitting pattern based on D-optimal model was used to find the desirability functions of the suggested design to assess the cross-interferences and the interactions between the factors. The fabricated sensor for determining the La(III) ions demonstrated a maximum nernstian slope equal to 19.70 mV.decade-1 along a linear range from 1.0×10−6 to 1.0×10−2 mol/L−1 and detection limit of 10−6 mol/L-1. The designed sensor was successfully tested in the pH range of 2-9 with suitable selectivity, fast response time (about 30 s) and long lifetime (over 2 months) was obtained without any deviation. The offered electrode was used successfully as an indicator in the potentiometric titration of La(III) with EDTA.

Lanthanum selective electrode, Multi-walled carbon nanotubes, Modified carbon paste electrode, Chitosan