Potentiometric sensors selective sensor

The principle of pH electrode sensing mechanisms which are based on glass or polymer membranes is well investigated and understood. Common to all potentiometric ion selective sensors, a pH sensitive membrane is the key component for a sensing mechanism. When the pH sensitive membrane separates the internal standard solution with a constant pH from the test solution, the potential difference E across the membrane is determined by the Nemst equation ... 

Ciosek et al. (2005) used potentiometric ion-selective sensors for discriminating different brands of mineral waters and apple juices. PC A and ANN classification were used as pattern recognition tools, with a test set validation (Ciosek et al., 2004b). In a subsequent study, the same research group performed the discrimination of five orange juice brands, with the same instrumental device. A variable selection was performed, by means of strategies based on PCA and PLS-DA scores. The validation was correctly performed with an external test set. 

It is important to note that if the detected species is hydrogen ion, then all aci-dobasic species are mutually interfering. Improved selectivity can be obtained by the judicial choice of the internal potentiometric element and to some extent by the selective permeability of the hydrophobic membrane. Thus, for example, for selective detection of HCN (pKa = 3.32) the internal element should be a potentiometric sensor selective to CN and the pH of the internal electrolyte should be at least two pH units above the pKa value (e.g., pH >5.5). In that case, practically all HCN is dissociated. 

Table 13.3 Potentiometric sensors selective to dissolved gases...

Potentiometric sensors -> Electrochemical sensors for which the - potential of the -> indicator electrode is measured against a -> reference electrode. The commonly used - pH-sensitive electrodes and -> ion-selective electrodes belong to the group of potentiometric sensors. Se also potentiometry. 

O. Gurtova, L. Ye and F. Chmilenko, Potentiometric propranolol-selective sensor based on molecularly imprinted polymer. Ana/. Bioanal. Chem., 405 (1) 287-295,2013. 

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... 

Chemically sensitized field effect transistor in which the effect of the interaction between the analyte and the active coating is transformed into a change of the source-drain current. The interactions between the analyte and the coating are, from the chemical point of view, similar to those found in potentiometric ion-selective sensors. 

Bandodkar, A.J., Hung, V.W.S., Jia, W., Valdes-Ramlrez, G., Windmiller, J.R., Martinez, A.G., Ramirez, J., Chan, G., Kerman, K., Wang, J., 2013. Tattoo-based potentiometric ion-selective sensors for epidermal pH monitoring. Analyst 138,123-128. 

The principles of chemical recognition have been widely used in analytical chemistry for the development of selective sensing devices. The recognition properties of several ionophores have been exploited to enable the design of advanced materials suitable for the preparation of fiber optic and potentiometric sensors. Specifically, sensors were prepaid by electrochemically growing poly[Co(II)tetra(oamino-phenyl)porphyrin] and poly[Co(II)tetra(p-hydroxyphenyl)porphyrin] on glassy carbon electrodes and indium(tin) oxide (TTO) sUdes. 

More recendy, two different types of nonglass pH electrodes have been described which have shown excellent pH-response behavior. In the neutral-carrier, ion-selective electrode type of potentiometric sensor, synthetic organic ionophores, selective for hydrogen ions, are immobilized in polymeric membranes (see Membrane technology) (9). These membranes are then used in more-or-less classical glass pH electrode configurations. 

Sources of Error. pH electrodes are subject to fewer iaterfereaces and other types of error than most potentiometric ionic-activity sensors, ie, ion-selective electrodes (see Electro analytical techniques). However, pH electrodes must be used with an awareness of their particular response characteristics, as weU as the potential sources of error that may affect other components of the measurement system, especially the reference electrode. Several common causes of measurement problems are electrode iaterferences and/or fouling of the pH sensor, sample matrix effects, reference electrode iastabiHty, and improper caHbration of the measurement system (12). 

Potentiometric instrnments are nsed most often when analyzing harmful contaminants in the air at production sites or in cities. Electrodes, whose potential is, as a rule, a linear fnnction of the logarithm of concentration of the substance to be determined (by Nemst s law), are the sensing elements in snch instruments. Most potentiometric sensors are highly selective. 

Ion-selective electrodes are membrane systems used as potentiometric sensors for various ions. In contrast to ion-exchanger membranes, they contain a compact (homogeneous or heterogeneous) membrane with either fixed (solid or glassy) or mobile (liquid) ion-exchanger sites. 

The disadvantages described above in terms of the irreversibility of the polyion response stimulated further research efforts in the area of polyion-selective sensors. Recently, a new detection technique was proposed utilizing electrochemically controlled, reversible ion extraction into polymeric membranes in an alternating galvanostatic/potentiostatic mode [51]. The solvent polymeric membrane of this novel class of sensors contained a highly lipophilic electrolyte and, therefore, did not possess ion exchange properties in contrast to potentiometric polyion electrodes. Indeed, the process of ion extraction was here induced electrochemically by applying a constant current pulse. 

FIGURE 4.11 Amplitude-time behavior of potential during calibration in 0.1 M Nad solution containing 50 mM TRIS (pH 7.40) with a pulsed galvanostatic sensor (a) and a classical potentiometric protamine-selective electrode (b) [54], Logarithmic protamine concentrations (mg l-1) are indicated on the traces. The first and last samples did not contain protamine. 

Detection of Li+ in artificial serum with a voltammetric Li-selective electrode in a flowthrough system was demonstrated [64], Lithium salts such as lithium carbonate have been extensively used for treatment of manic depressive and hyperthyroidism disorders. The therapeutic range of Li concentration is generally accepted to be 0.5-1.5mM in blood serum. The authors used normal pulse voltammetry in which a stripping potential was applied between pulses in order to renew the membrane surface and expel all of the extracted ions from the membrane, similar to galvanostatically controlled potentiometric sensors described above. Unfortunately, the insufficient selectivity... 

The concept of light addressable potentiometric sensors (LAPS) was introduced in 1988 [67], LAPS is a semiconductor-based sensor with either electrolyte-insulator-semiconductor (EIS) or metal-insulator-semiconductor (MIS) structure, respectively. Figure 4.13 illustrates a schematic representation of a typical LAPS with EIS structure. A semiconductor substrate (silicone) is covered with an insulator (Si02). A sensing ion-selective layer, for instance, pH-sensitive S3N4, is deposited on top of the insulator. The whole assembly is placed in contact with the sample solution. 

P. Buhlmann, E. Pretsch, and E. Bakker, Carrier-based ion-selective electrodes and bulk optodes. 2. Ionophores for potentiometric and optical sensors. Chem. Rev. 98, 1593-1687 (1998). 

R.D. Johnson and L.G. Bachas, Ionophore-based ion-selective potentiometric and optical sensors. Anal. Bioanal. Chem. 376, 328-341 (2003). 

Y. Mourzina, Y. Ermolenko, T. Yoshinobu, Y. Vlasov, H. lwasaki, and MJ. Schoning, Anion-selective light-addressable potentiometric sensors (LAPS) for the determination of nitrate and sulphate ions. Sens Actuators, B 91, 32—38 (2003). 

Y. Qin, S. Peper, A. Radu, A. Ceresa, and E. Bakker, Plasticizer-free polymer containing a covalently immobilized Ca2+-selective ionophore for potentiometric and optical sensors. Anal. Chem. 75, 3038—... 

P.G. Boswell and P. Buhlmann, Fluorous bulk membranes for potentiometric sensors with wide selectivity ranges observation of exceptionally strong ion pair formation. J. Am. Chem. Soc. 127, 8958—8959 (2005). 

Besides, potentiometric sensors with ion-selective ionophores in modified poly(vinyl chloride) (PVC) have been used to detect analytes from human serum [128], Cellular respiration and acidification due to the activity of the cells has been measured with CMOS ISFETS [129], Some potentiometric methods employ gas-sensing electrodes for NH3 (for deaminase reactions) and C02 (for decarboxylase reactions). Ion-selective electrodes have also been used to quantitate penicillin, since the penicillinase reaction may be mediated with I or GST. 

Particular cases are potassium selective potentiometric sensors based on cobalt [41] and nickel [38, 42] hexacyanoferrates. As mentioned, these hexacyanoferrates possess quite satisfactory redox activity with sodium as counter-cation [18]. According to the two possible mechanisms of such redox activity (either sodium ions penetrate the lattice or charge compensation occurs due to entrapment of anions) there is no thermodynamic background for selectivity of these sensors. In these cases electroactive films seem to operate as smart materials similar to conductive polymers in electronic noses. 

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