Ion selective sensors

Lead(II) sulfide occurs widely as the black opaque mineral galena, which is the principal ore of lead. The bulk material has a band gap of 0.41 eV, and it is used as a Pb " ion-selective sensor and IR detector. PbS may become suitable for optoelectronic applications upon tailoring its band gap by alloying with II-VI compounds like ZnS or CdS. Importantly, PbS allows strong size-quantization effects due to a high dielectric constant and small effective mass of electrons and holes. It is considered that its band gap energy should be easily modulated from the bulk value to a few electron volts, solely by changing the material s dimensionality. 

According to Eq. (1) the steady-state current across a micro-ITIES is proportional to the bulk concentration of the transferred species. Thus, the micro-ITIES can function as an amperometric ion-selective sensor. Similarly, the peak current in a linear sweep voltam-mogram of ion egress from the micropipette obeys the Randles-Sevcik equation. Both types of measurements can be useful for analysis of small samples [18a]. 

Y. Qin and E. Bakker, A copolymerized dodecacarborane anion as covalently attached cation exchanger in ion-selective sensors. Anal. Chem. 75, 6002-6010 (2003). 

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 ... 

Since 1966, when Stefanac and Simon (3) developed the first electrodes of this type containing macrotetrolides, valinomycin, and other antibiotics as the active components, the analytical potential of these ion selective sensors has been generally recognized, and forms incorporating various electrically neutral ligands specific for K+ (3,86,87,89,107—110, 118, 119), NHj 85, 112), Ba2+ 113, 114), and other cations 115, 117) have found practical application (Table 9). 

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. 

Ion-selective sensors for chloride are commercially available [103]. Both fundamental and practical information concerning the theory, design, and operation of chloride-selective electrodes is available from a recent textbook [57]. Sensor membranes for potentiometric chloride detection have been formed from Ag2 S (as ion... 

This interface is also known as the perm-selective interface (Fig. 6.1a). It is found in ion-selective sensors, such as ion-selective electrodes and ion-selective field-effect transistors. It is the site of the Nernst potential, which we now derive from the thermodynamic point of view. Because the zero-current axis in Fig. 5.1 represents the electrochemical cell at equilibrium, the partitioning of charged species between the two phases is described by the Gibbs equation (A.20), from which it follows that the electrochemical potential of the species i in the sample phase (S) and in the electrode phase (m) must be equal. 

Clinical analysis of blood gases and electrolytes by ion-selective sensors... 

Electrochemical ion-selective sensors (ISSs), including potentiometric ion-selective electrodes (ISEs) and potentiometric or amperometric gas-selective sensors (GSSs), attracted the interest of clinical chemistry because they offer fast, reliable, inexpensive analytical results in service-free automated analyzers. In this way, the electrochemical sensors satisfy the present demands of central hospital laboratories and peripheral point-of-care medical service points, such as bedside, emergency or first-contact healthcare centers. 

Such an ISFET was originally used for detecting pH changes but by casting with ion selective membranes a lot of different ion-selective sensors can be obtained in principle [38,39]. Even a multi-parameter electrolyte sensitive chip for clinical applications was invented [39]. 

A typical matrix material for ion selective sensors and sensors utilising the ion selective response, is PVC. Macrocyclic receptor molecules are dissolved in a plasticiser as solvent and retained within the polymeric matrix. The ratio of membrane components is critical (39) and deviation leads to excess leaching of the plasticiser or insufficient receptor molecule to obtain a response. The PVC matrix is only able to retain a limited proportion of plasticiser and the ionophore has limited solubility in the plasticiser. In fact the most stable membranes have the lowest proportion of plasticiser, but these are also the least sensitive and selective, since they contain a low ionophore ratio some stability must be lost at the expense of sensitivity (Duschl C and Hall EAH Hall, unpublished data). 

Whereas SECM usually uses tips that pass a current in amperometric or voltammetric mode, an important related application uses passive ion-selective sensor tips which can be used for mapping two-dimensional and even three-dimensional ion distributions and concentration profiles over the surface, of species such as protons and zinc ions [53]. 

Koncki, R. Hulanicki, A. Glab, S., Biochemical modifications of membrane ion-selective sensors, Trends Anal. Chem. 1997, 16, 528-536... 

The selectivity factor, K " , is a measure of the preference of the ion-selective sensor for the interfering ion j relative to the primary ion i to be measured. A selectivity factor below 1 indicates that the preference is for the primary ion i. Two methodologies are used to measure the selectivity factor experimentally ... 

Since the incorporation of a certain anion would take place for the system to reach equilibrium at the polymer coated electrode, the potential at the membrane-electrolyte interface would indicate the amount of anions incorporated. Indeed, a few groups of investigators realized that this was the case [274-276]. The potential at the PPy film coated electrode was shown to vary depending on the concentration of the Fe /Fe + pair [274], hydroxide ion [275], and many other anions and cations [276]. Recently, Hutchins and Bachas have developed a nitrate ion selective sensor using a PPy film coated electrode [277]. The electrode showed a near Nemstial slope of —56 1 mV per decade, good dynamic linearity, and a detection limit of (2 1) X 10 M for nitrate. The selectivity coefficients over CIO4 and 1 were 5.7 x 10 and 5.1 X 10 respectively. 

Potentiometry—the measurement of electric potentials in electrochemical cells—is probably one of the oldest methods of chemical analysis still in wide use. The early, essentially qualitative, work of Luigi Galvani (1737-1798) and Count Alessandro Volta (1745-1827) had its first fruit in the work of J. Willard Gibbs (1839-1903) and Walther Nernst (1864-1941), who laid the foundations for the treatment of electrochemical equilibria and electrode potentials. The early analytical applications of potentiometry were essentially to detect the endpoints of titrations. More extensive use of direct potentiometric methods came after Haber developed the glass electrode for pH measurements in 1909. In recent years, several new classes of ion-selective sensors have been introduced, beginning with glass electrodes more or less selectively responsive to other univalent cations (Na, NH ", etc.). Now, solid-state crystalline electrodes for ions such as F , Ag", and sulfide, and liquid ion-exchange membrane electrodes responsive to many simple and complex ions—Ca , BF4", CIO "—provide the chemist with electrochemical probes responsive to a wide variety of ionic species. 

Legin, A.V., Rudnitskaya, A.M., Vlasov, Y. G., Di Natale, C., D Amico, A. The features of the electronic tongue in comparison with the characteristics of the discrete ion-selective sensors. Sens. Actuators B 58, 464-468 (1999)... 

Biosensors, ion selective sensors, medical elec- www.dupont.com... 

Wall-embedded ion-selective sensors are more suitable for routine operations. The sensing surface can be made to be either a section of a glass or plastic tubular electrode or a part of a conduit through which the sample/carrier solution flows. The reference electrodes are easily located somewhere downstream. Two designs, suitable for FI applications. are shown in Figs. 2.15 and 2.16. 

Metalloporphyrins, one carbon larger but structurally analogous to the corrin ring of vitamin B12, exhibited unique anion ionophore properties when incorporated into a polymer membrane. Mn(III), Co(III), Ru(II), and Sn(IV) porphyrin-based ion-selective sensors exhibit high selectivity for thiocyanate, nitrite/thiocyanate, thiocyanate and siicylate, respectively. doo-io7,i 10-114 nature of the... 

The miniaturization of sensors is an advantage for in vivo measurements. A miniaturized ion-selective sensor chip for potassium, mounted in a catheter or cannula and integrated onto an Si chip containing valinomycin with a Ag/AgCl reference electrode coated with a poly(hydroxyethyl methacrylate) layer, has been used in in vivo determination of K in blood or serum. 

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