Environmental potentiometric sensors

Design of Molecular Recognition Elements for Environmental Potentiometric Sensors... 

Ion selective electrodes (ISEs) or, in a wider sense, potentiometric sensors have demonstrated its usefulness to yield information of chemical species in automated and autonomous operation. This feature has fostered their use in the monitoring of numerous processes, in the industrial, clinical and environmental fields, among others. Current practice with these devices relies on sensors with high selectivity only in this way, a simple determination of a single ion is possible in presence of its interferents. Some reluctances on the broadening of their use are surely due to the fact that ISEs are not specific but show high selectivity towards a reduced number of ions. 

In view of the above features, oscillometric (conductometric) and potentiometric sensors seem to be best suited for use in industrial and environmental monitors among the electro-analytical techniques. Oscillometric and conductometric sensors fulfil the first and third requirement, the technical problems in connectin with calibration axe not too difficult. There are, however, problems with the fourth requirement, because impedance and the complex dielectric constant both depend on all constituents present, and because these properties do not only depend on one single factor but on several factors. The electrical equivalent circuit for the oscillometric capacities is given in Fig.l. The expression of the h.f. conductance, G, is as follows ... 

The most representative potentiometric sensors are ion-selective electrodes (ISEs), as shown in Fig. 1. They are common in environmental analysis today and some typical ISEs are summarized in Table 1. The measurement of the ion of interest depends on the potential difference across the membrane between the sample solution and the inner reference electrolyte (Fig. 1 left, iimer reference electrode). The membrane potential obtained from the difference between the ISE and the reference electrode (Fig. 1 right,... 

Ion-selective electrodes (ISEs) constitute an example of potentiometric sensors that offer several advantages over other analytical techniques for the analysis of environmentally important ions. Specifically, the sensing platform of a membrane-based ISE consists of an ion carrier (ionophore) entrapped within a liquid polymeric membrane. The membrane does offer some interaction with numerous species, but the main interaction governing the selectivity of the sensor is between the analyte/interferences and the ionophore. Once an ionophore that offers the preferred selectivity has been developed and the polymer components that are ionophore-compatible have been optimized, the production of a functional ISE is rather facile and rapid. Presently, ISEs have been reported for several species including metal ions, anions, surfactants, and gases (5). 

Sulfadimethoxine (SMD) is a dmg frequently used to prevent the spreading of diseases in freshwater fish aquaculture, but its control is important to avoid environmental contamination. A potentiometric sensor selective to SMD was built inside a micropipette tip [211] by immersing a PVC membrane loaded with 1 % of meTO-tetra(phenyl)porphyrinate manganese(lll) chloride in a reference solution. This electrode gave near Nemstian response (54.1 mV/decade) and excellent detection limit (2.4 x 10 mol L ) was attained. For the quantification of SO2, a selective electrode was prepared by incorporation of Cio-(tetraphenyl)porphyr-inate zinc(ll) in a PVC membrane plasticized with 2-nitrophenyl-phenylether [212]. The new electrode presented a selective response to sulphite, with good linearity in an interval larger than four decades of concentration and slope of -59.5 mV per decade, and detection limit of 3.7 x 10 mol L . This sensor presented high... 

Electronic tongue systems for remote environmental monitoring applications have been presented in several applications. A new approach in the chemical sensor field consists in the use of an array of nonspecific sensors coupled with a multivariate calibration tool which may form a node of a sensor network. The proposed arrays were made up of potentiometric sensors based on polymeric membranes, and the subsequent cross-response processing was based on a multilayer artificial neural network model as proposed by Mimendia et al. who described environmental monitoring of ammonium as a pollutant plus alkaline ions at different measuring sites in the states of Mexico and Hidalgo (Mexico), and monitoring of heavy metals (Cu ", Pb ", Zn ", and Cd " ) in open-air waste streams and rivers. 

Electrochemical sensors play a crucial role in environmental and industrial monitoring, as well as in medical and clinical analysis. The common feature of all electroanalytical sensors is that they rely on the detection of an electrical property (i.e., potential, resistance, current) so that they are normally classified according to the mode of measurement (i.e., potentiometric, conductometric, amperometric). A number of surveys have been published on this immense field. The reader may find the major part of the older and recent bibliography in the comprehensive reviews of Bakker et al. [109-111]. Pejcic and De Marco have presented an interesting survey... 

Potentiometric ion-selective electrodes (ISEs) are one of the most important gronps of chemical sensors. The application of ISEs has evolved to a well-established rontine analytical technique in many fields, inclnding clinical and environmental analysis, physiology, and process control. The essential part of ISEs is the ion-selective membrane that is commonly placed between two aqueous phases, i.e the sample and inner solutions that contain an analyte ion. The membrane may be a glass, a crystalline solid, or a liquid (1). The potential difference across the membrane is measured with two reference electrodes positioned in the respective aqueous phases... 

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