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Um sensor altamente seletivo para Cu(II) usando 4-amino-6-metil-1,2,4-triazina-5-ona-3-tiona (AMTOT) como material seletivo, foi desenvolvido utilizando uma membrana de PVC. O eletrodo exibe um intervalo dinâmico linear entre 1,0×10 -1 e 1,0×10 -6 mol L -1 , com resposta Nernsteniana de 29,3 ± 0,6 mV por década e um limite de detecção de 6,2×10 -7 mol L -1 . A resposta do eletrodo é independente do pH, no intervalo entre 2,5 e 7,0. O sensor possui a vantagem de apresentar um tempo de condicionamento pequeno, uma rápida velocidade de resposta (< 20 s) e especialmente, uma boa seletividade frente a metais pesados e de transição, e a alguns cátions mono, di e trivalentes. O eletrodo pode ser usado por até 9 semanas sem consideráveis divergências de potencial. O eletrodo proposto foi aplicado com sucesso na determinação de cobre em águas de descarte, oriundas de plantas eletroquímicas de cobre e como eletrodo indicador na titulação potenciométrica de íons Ca(II) com EDTA.A highly Cu(II) ion-selective PVC membrane sensor based on 4-Amino-6-methyl-1,2,4-triazin-5-one-3-thione (AMTOT) as an excellent sensing material was developed. The electrode exhibits a linear dynamic range between 1.0×10 -1 and 1.0×10 -6 mol L -1 , with a near Nernstian slope of 29.3 ± 0.6 mV per decade and a detection limit of 6.2×10 -7 mol L -1 . The sensor response is independent of the pH of the solution in the pH range of 2.5 -7.0. The sensor possesses the advantages of short conditioning time, fast response time (<20 s), and especially, very good selectivity towards transition and heavy metal, and some mono, di and trivalent cations. The electrode can be used for at least 9 weeks without any considerable divergence in the potentials. The proposed electrode was successfully applied to the determination of copper in wastewater of copper electroplating samples and as an indicator electrode in potentiometric titration of Ca(II) ions with EDTA.Keywords: potentiometry, copper sensor, PVC membrane, 4-amino-6-methyl-1,2,4-triazin-5-one-3-thione IntroductionDuring the last decade, there has been a renewed resurgence in developing potentiometric membrane electrodes as devices for rapid, accurate, low cost and non destructive analysis of different samples with small volume samples.Due to the necessary need for selective copper measurements in many copmplex biological systems, 1,2 geochemical, 3 environmental, medicinal and industrial samples, 4 the search for new selective and sensitive PVCmembrane electrodes for its quick measurement is still a challenging goal. We have recently reported a number of highly selective and sensitive membrane sensors for various metal ions. [23][24][25] In this paper, we wish to introduce a highly copper(II)-selective sensor based on 4-Amino-6-methyl-1,2,4-triazin-5-one-3-thione (AMTOT), as a novel neutral ionophore for monitoring of copper in industrial samples (Figure 1). Experimental ReagentsReagent grade 2-nitrophenyl octyl ether (NPOE), dibutyl phthalate (DBP), benzyl acetate (BA), nitrobenzene (NB), sodium tetraphen...