Highly efficient potentiometric sensing device for gadolinium based on Tetraazacyclododecane-1, 4, 7, 10 -tetraaceticacid crown ether and multiwalled carbon nanotube composite

Abstract

A hydrophilic cavity presents in tetraazacyclododecane-1, 4, 7, 10-tetraaceticacid crown ether (DOTA) provides the opportunity for Gadolinium (Gd3+) transfer from an aqueous medium to a lipophilic phase and mimic the ionophoric properties due to strong coordinating link. Therefore, we have developed Gd3+ ion selective electrode (ISE) incorporating synthesized nanocomposite of DOTA as an ionophore and multiwalled carbon nanotube (MWCNT) as signal enhancer in poly vinyl chloride (PVC) membrane sensor employing potentiometry. The composite DOTA-MWCNT was characterized by scanning electron microscopy (SEM). The Nernstian slope of 20.05 ± 0.18 mV per decade with linear range 1 × 10-2 to 1 × 10-8 M and the detection limit was found to be 7.2 ± 0.16 × 10-9 M. This electrode has an excellent selectivity over mono, bi, tri and tetravalent interferent metal species. The proposed sensor was favourably applied as an indicator electrode in the titration of Gd3+ ions with EDTA and recovery of gadolinium (III) from diverse synthetic samples. The presence of four ionizable carboxylic acids groups imparts advantages to DOTA-MWCNT composite in the formation of strong complexes and enhanced solubility of Gd3+ which became the basis for in-vivo analysis of Gd3+ in pharmaceutical and soil samples. DOTA-MWCNT as host forms 1:1 chelate complex with guest Gd3+ employing square wave voltammetry. The stability constant (Log K = 25.41) and Gibbs free energy (DG) of DOTA-MWCNT - Gd3+ complex was calculated which established exothermic and spontaneous inclusion mechanism. The higher stability constant obtained for DOTA-MWCNT chelate complex can provide the opportunity to researchers of biomedical science to minimize/control the amount of free Gd3+ release in the human body through the process of drug delivery.