Determination of Er3+ Ion at Nano Level Based on Newly Synthesized Schiff Base As a Neutral Carrier By Coated Graphite Electrode
Authors: Upadhyay Anjali , Singh Ashok KUMAR , Bandi Koteswara RAO , Jain Ajay Kumar 
Published: February 2020

Abstract

The rare earth elements (REEs) are mainly of two series Lanthanides and Actinides. Despite of their name REEs are not so rare in environment, they widely distributed in throughout the earth’s crust in low concentration. The REEs have significant industrial application as competitive to transition elements and wide application have been found in bioinorganic, inorganic chemistry. Erbium is mainly used as laser beams to resurfacing skin, transdermal drug delivery, transdermal peptide delivery, skin vaccination and enhances the RNA delivery. It is estimated that the erbium concentration of the earth’s crust reaches 24 ppm. The commercial sources of erbium are monazite and bastnasite. Even though the conclusion of the investigators, the rare earth elements are considered as low acute toxicity rating, these causes several problems to living species. Due to their enhanced discharge, toxic properties and other adverse effects, determination of erbium is essential in a variety of environmental samples.

A number of instrumental techniques such as second order derivative spectrophotometry, third-derivative spectrophotometry, X-ray fluorescence, graphite furnace atomic spectrometry techniques, inductively coupled plasma mass spectrometry, rutherford backscattering spectrometry and spectrophotometric determination are available for its estimation. These methods provide accurate determination of erbium content but involve large infrastructure backup and support of expertise. We found ion-selective electrode to overcome these problems. Ion-selective electrodes are electrochemical ideal sensors in many respects for use in the analysis of industrial and environmental samples.

Plasticized membranes using N-(-3-((thiazol-2-ylimino)methyl)benzylidene)thiazol-2-amine (S1) and 5-((-3-((5-mercapto-1,3,4-thiadiazol-2-ylimino)methyl)-benzylidene)amino)-1,3,4-thiadiazole-2-thiol (S2) have been prepared and explored as Er3+ selective electrodes. Effect of various plasticizers viz. dibutylphthalate (DBP), tri-n-butylphosphate (TBP), dioctylphthalate (DOP), acetophenone (AP), 1-chloronapthalene (1-CN), o-nitrophenyloctylether (o-NPOE), and anion excluders viz. sodium tetraphenylborate (NaTPB) and potassium tetrakis-p-(chlorophenyl)borate (KTpClPB) was studied in detail and improved performance was observed. Optimum performance was observed for the membrane electrode having a composition of S2: PVC: o-NPOE: KTpClPB in the ratio of 4: 38: 55: 3 (w/w, mg). The performance of the polymeric membrane electrode (PME) based on S2 was compared with coated graphite electrode (CGE). The electrodes exhibit Nernstian slope for Er (III) ions with limit of detection of 5.4 × 10-8 mol L−1 for PME and 6.1 × 10-9 mol L−1 for CGE. The response time for PME and CGE was found to be 12 s and 9 s respectively. The potentiometric responses are independent of the pH of the test solution in the pH range 4.0-9.0 for PME and 3.0-9.5 for CGE. The CGE could be used for a period of 7 weeks. The practical utility of the CGE has been demonstrated by its usage as an indicator electrode in potentiometric titration of EDTA with Er (III) solution and determination of F- ion in mouthwash solution. The proposed electrode was also successfully applied to the determination of Er3+in water, binary mixtures.

Table 1. Response characteristics of Er3+ ion selective electrodes based on PME and CGE.

Properties
Electrode Response

PME
CGE

Working concentration range (mol L-1)
7.9 × 10-8 - 1.0 × 10-1

9.4 × 10-9 - 1.0 × 10-1

Detection limit (mol L-1)
5.4 × 10-8

6.1 × 10-9

Slope (mV decade-1

of activity)
19.8 ± 0.4
19.6 ± 0.3

Response time (s)
12
9

pH range
4.0-9.0
3.0-9.5

Fig. 1. Structure of ligands N-(-3-((thiazol-2-ylimino)methyl)benzylidene)thiazol-2-amine (S1) and 5-((-3-((5-mercapto-1,3,4-thiadiazol-2-ylimino)methyl)-benzylidene)amino)-1,3,4-thiadiazole-2-thiol (S2)