Development of optochemical sensors for Hg(II), based on immobilized 2-(5-amino-3,4-dicyano-2 H-pyrrol-2-ylidene)-1,1,2-tricyanoethanide

• Published in: Sensors and actuators. B, Chemical Chemical, 1997-07, Vol.42 (1), p.39-46
• Main Authors: Flamini, Alberto, Panusa, Alessia
• Format: Article
• Language: English
• Subjects: Analytical chemistry; Chemistry; Exact sciences and technology; General, instrumentation; Mercury; Pyrrolizinato complexes; Sensors; Tetracyanoethylene; Thin-films
• ISSN: 0925-4005; 1873-3077
• DOI: 10.1016/S0925-4005(97)80310-3

The dye 2-(5-amino-3,4-dicyano-2 H-pyrrol-2-ylidene)-1,1,2-tricyanoethanide (L′, C 11H 2 N 7 −  , λ max=549 nm), is a specific ligand for Hg 2+ in water, undergoing a colour change from violet to blue on the formation of the corresponding monochelated pyrrolizanto [>HgL] complex ( λ max=650 nm). The reactivity of L′ with several Hg(II)-salts (Hg(H 2O) 6·2ClO 4, HgAc 2, HgCl 2, CH 3HgAc) and with a number of salts of different metal cations (M +=Ag; M 2+=Fe, Co, Ni, Cu, Zn, Cd, Sn, Pb, Pd, Pt; M 3+=Ru, Rh, Ir, Au, La) has been studied in homogeneous solution and in a polymeric sol–gel thin film (thickness ∼600 Å, C L′=0.3 M) of polyvinylformal/silica (PVF/SiO 2), obtained by dip-coating the appropriate THF solution of AsPh 4L′ on a glass support. In most cases a parallel reactivity has been observed: L′ is sensitive mostly to the perchlorate among the Hg(II)-salts and the interference from M z+ consists mainly in a degradation of L′ with a consequent fading. The cross interferences of Hg 2+ from Au 3+ and Cu 2+ have also been examined and have been found distinctly different in the two systems. The effect of the matrix material has been studied by ESCA analysis of L′-doped films after being soaked in the appropriate water solutions. PVF/SiO 2, being a non-porous material, makes the response of L′-doped film to Hg 2+ rather slow with associated a detection limit lower on the order of one magnitude than that of L′ in homogeneous solution (10 ppm for a response time of 10 min). The L′-doped film can be regenerated from the corresponding [>HgL]-doped film, exposing the latter to the vapour of a concentrated HCl aqueous solution.