Highly Selective Nd(III) Sensors: Novel Macrocyclic Compounds for Potentiometric Determination of Neodymium

Conductometric studies on the complexation properties of two newly synthesized lariat ethers viz 1,5‐di(cyanoethane)‐2,4 : 7,8 : 13,14‐tribenzo‐1,5‐diaza‐9,12‐dioxacyclopentadeca‐2,7,13‐triene (L 1 ) and 1,5‐di(cyanoethane)‐2,3,4‐pyridine‐7,8 : 13,14‐dibenzo‐1,3,5‐triaza‐9,12‐dioxa cyclopentadeca‐2,7,13‐triene (L 2 ) towards various metal ions in acetonitrile solutions revealed the formation of 1 : 1 ligand metal complexation. These compounds were explored as neutral ionophores for the fabrication of Nd 3+ selective and sensitive membrane coated graphite electrodes (CGEs). Among all the electrodes prepared, CGEs with membrane composition L 1 (5%) : NaTPB(3%) : NPOE (57%) : PVC (35%) and L 2 (5%) : NaTPB(3%) : NPOE (53%) : PVC (39%) showed best performance. Both the electrodes showed Nernstian response towards Nd 3+ ions over a wide concentration range with detection limits 3.8×10 −8  mol L −1 and 1.6×10 −8  mol L −1 respectively. These electrodes showed a fast response time of <15 s and could be used over a period of three months without significant divergence in their characteristics. The proposed electrodes revealed very good selectivity for Nd 3+ ions over several ions. However, higher concentration of Co 2+ , La 3+ , Pr 3+ and Yb 3+ caused some interference. The potentiometric response of these electrodes was excellent in the range of pH 3.5 to 7.6 and they could tolerate up to 20% (v/v) nonaqueous media in the test solutions. These electrodes were used successfully as indicator electrode in the potentiometric titration of Nd 3+ against EDTA and also in the quantitative determination of Nd 3+ ions from binary mixtures and water samples.