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Copper (II) ion chemical sensors based on pyridine-thiourea derivatives; N-pyridyl-N'-(biphenyl-4-carbonyl)thiourea (L1), and N-pyridyl-N'-(3,5-dimethyoxybenzoyl)thiourea (L2) were synthesised, characterised, and studied as ionophores in the form of thin-films PVC membranes. The ionophores exhibited good responses towards copper (II) ion over the concentration range of 2 x 10 -4 to 10 x 10 -4 M with a limit of detection 1.34 x 10 -5 to 1.48 x 10 -5 M. The proposed sensors L1 and L2 revealed good performance in term of reproducibility and regeneration of the ionophores with low relative standard deviation (RSD) values 4.17 % and 2.74 % respectively. Besides, quantum chemical calculation performed using Gaussian 09 program indicated the oxygen (O) atom from carbonyl moiety (C=O) was the most favourite reactive site and mainly responsible for ionophore-Cu(II) interaction. The obtained data revealed pyridine-thiourea derivatives offered great potential as ionophore for the detection of Cu (II) ion.

Dithizone-PVC membrane was constructed and utilized as an ionophore reagent material for chemically modified silver (Ag) electrode. The modified electrode was characterized using cyclic voltammetry where the electrochemical behaviour of dithizone modified Ag electrode surface was investigated in the range of -0.6 to +0.6 V with 0.1 M KCl as supporting electrolyte. Comparative studies towards metal ions Cu 2+ , Fe 2+ and Pb 2+ exhibited good responses for redox reactions with linear relationship between peak currents and concentrations. The correlation coefficients obtained were 0.9800, 0.9944 and 0.9949 while the evaluated limits of detection were 8.3 x 10 -7 M, 4.7 x 10 -7 M and 7.6 x 10 -7 M respectively.Keywords: PVC membrane, dithizone (1,5-diphenylthiocarbazone), cyclic voltammetry, redox reactions Abstrak Membran PVC-Ditizon telah dibina dan digunakan sebagai bahan reagen ionofora bagi elektrod perak (Ag) yang diubahsuai secara kimia. Elektrod yang diubahsuai telah dicirikan menggunakan voltametri berkitar di mana sifat elektrokimia bagi ditizon yang diubahsuai pada permukaan elektrod Ag telah dikaji di dalam julat -0.6 ke +0.6 V dengan 0.1 M KCl sebagai elektrolit sokongan. Kajian perbandingan terhadap ion-ion logam Cu 2+ , Fe 2+ dan Pb 2+ mempamerkan respon yang baik bagi tindak balas redoks dengan hubungan linear antara arus-arus puncak dan kepekatan. Pekali korelasi yang diperolehi adalah 0.9800, 0.9944 dan 0.9949 manakala had pengesanan yang diukur adalah 8.3 x 10 -7 M, 4.7 x 10 -7 M dan 7.6 x 10 -7 M masing-masing.Kata kunci: membran PVC, ditizon (1,5-difeniltiokarbazon), voltametri berkitar, tindakbalas redoks Introduction Heavy metals pollution in environment is a global issue that has been discussed over the years. Heavy metals can enter the environment by both natural and anthropogenic sources including mining, agrochemicals, sewage and sludge applications and also industrial activity. Copper (Cu