Potentiometric Determination of Silver(I) by Selective Membrane Electrode Based on Derivative of Porphyrin

Abstract

Ion-selective electrodes permit the potentiometric measurement of the activity of a given ion in the presence of other ions. Construction and then application of an ion-selective electrode as a potentiometric sensor offers interesting advantages such as speed, fast response, simplicity, low cost and wide linearity range. These characteristics have inevitably led to sensors for ionic species. 1 Specific metal-ligand interactions are among the most important recognition mechanisms that can be utilized in the development of potentiometric sensors. 2 Such interactions have been used in the development of cation-and anionselective electrodes based on different ionophores.The porphyrins are a class of naturally occurring macrocyclic compounds, which play a very important role in the metabolism of living organisms. The porphyrin molecule contains four pyrrole rings linked via methene bridges. The porphyrin nucleus is a tetradentate ligand in which the space available for a coordinated metal has a maximum diameter of approximately 3.7 Å. 3 When coordination occurs, two protons are removed from the pyrrole nitrogen atoms, leaving two negative charges. The porphyrin ring system is very stable and exhibits aromatic character. 4 The need for highly sensitive and selective determination of silver ion arises from both its economic value and its long-term toxicity toward human beings. It is known that silver inactivates sulfhydryl enzymes and also combines with amine, imidazole and carboxyl groups. Further, silver has many technical uses such as in photography, dentistry, and the electronic industry. It is also increasingly being used in the field of medicine. [5][6][7] Also, the multi-purpose nature of silver makes its analysis in, and recovery from, waste material of increasing importance. The chemical recognition of metal ions is a very difficult task due to their ability to show several coordination numbers and their affinity towards different coordination centers. The d 10 transition metal ions, Ag + and Hg 2+ , display singular coordination characteristics. 8 A silver ion-selective electrode finds applications in environmental monitoring, wastewater analysis and for the determination of some anions such as chloride, bromide and iodide. A group of polythiacrown ethers and acyclic polythia compounds have been utilized for the measurement of Ag + . [9][10][11] It is also found that some sulfur and/or nitrogen-containing calix and resorc arene-based PVC membrane electrodes exhibit good selectivity toward Ag + ion over alkali metal ions. 12-14 A survey of the literature revealed that porphyrin compounds showed selective complexation with metals [for example meso-tetra(4-pyridyl)porphyrin (it has similar structure with ionophore mesotetraphenylporphyrin [H2T(4-CH3)]PP) showed selective complexation with Ag + ] and therefore may be used as electroactive materials for the fabrication of membranes in ISEs. 15 In this article, we report the use of, mesotetraphenylporphyrin [H2T(4-CH3)]PP as a highly selective neutral ion carrier f...

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