Ion-selection electrode technology

With the development of ion-selection electrode technology (ISE), a means became available to directly measure (no dilution) sodium and potassium in the presence of clinical samples containing a significant amount of protein or lipids. Because of non-aqueous components in the sample matrix, the volume occupied by sodium and potassium ions is less than the total volume of the sample. When using a technique that requires dilution (flame photometry) or utilizes dilution (indirect-ISE), a lower concentration is observed than that obtained with direct-ISE. In as much as the bias can be clinically significant (up to 1% in some instances) it is important that the method used be taken into accoimt. ... 

Most of the analytes (pC02, Na , K, Ca , and pH) are determined by potentiometric measurements using membrane-based ion-selective electrode technology. The hematocrit is measured by electrolytic conductivity detection, and p02 is determined with a Clark voltammetric sensor (see Section 23B-4). Other results are calculated from these data. 

This feature shows how modern ion-selective electrode technology coupled with computer control of the measurement process and data reporting can be used to provide rapid, essentia] measurements of analyte concentrations in whole blood at the patient s bedside. 

Davenport, J.R. and Jabro, J.D. (2001) Assessment of hand held ion selective electrode technology for direct measurements of soil chemical properties. Commun. Soil Sci. Plant Anal, 32, 3077-3085. 

National Institute of Standards and Technology (NIST). The NIST is the source of many of the standards used in chemical and physical analyses in the United States and throughout the world. The standards prepared and distributed by the NIST are used to caUbrate measurement systems and to provide a central basis for uniformity and accuracy of measurement. At present, over 1200 Standard Reference Materials (SRMs) are available and are described by the NIST (15). Included are many steels, nonferrous alloys, high purity metals, primary standards for use in volumetric analysis, microchemical standards, clinical laboratory standards, biological material certified for trace elements, environmental standards, trace element standards, ion-activity standards (for pH and ion-selective electrodes), freezing and melting point standards, colorimetry standards, optical standards, radioactivity standards, particle-size standards, and density standards. Certificates are issued with the standard reference materials showing values for the parameters that have been determined. 

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. 

Lead Telluride. Lead teUuride [1314-91 -6] PbTe, forms white cubic crystals, mol wt 334.79, sp gr 8.16, and has a hardness of 3 on the Mohs scale. It is very slightly soluble in water, melts at 917°C, and is prepared by melting lead and tellurium together. Lead teUuride has semiconductive and photoconductive properties. It is used in pyrometry, in heat-sensing instmments such as bolometers and infrared spectroscopes (see Infrared technology AND RAMAN SPECTROSCOPY), and in thermoelectric elements to convert heat directly to electricity (33,34,83). Lead teUuride is also used in catalysts for oxygen reduction in fuel ceUs (qv) (84), as cathodes in primary batteries with lithium anodes (85), in electrical contacts for vacuum switches (86), in lead-ion selective electrodes (87), in tunable lasers (qv) (88), and in thermistors (89). 

Electroanalytical chemistry is one of the areas where advantage of the unique properties of SAMs is clear, and where excellent advanced analytical strategies can be utilized, especially when coupled with more complex SAM architectures. There are a number of examples where redox reactions are used to detect biomaterials (357,358), and where guest—host chemistry has been used to exploit specific interactions (356,359). Ion-selective electrodes are an apphcation where SAMs may provide new technologies. Selectivity to divalent cations such as Cu " but not to trivalent ions such as Fe " has been demonstrated (360). 

Dinten O., Experimental and theoretical contributions in order to improve ion-selective electrodes based on PVC liquid membranes in terms of membrane technology, ETH Ph.D. thesis No. 8591, 1988. 

Ion-selective electrode research for biomedical analysis is no longer the relatively narrow, focused field of identifying and synthesizing ionophores for improved selectivity and the integration of ion-selective electrodes into clinical analyzers and portable instruments. These efforts have matured now to such an extent that they can teach valuable lessons to other chemical sensing fields that are just emerging technologies. 

Membranes. Photopolymer chemistry is being applied to the design and manufacture of a variety of membrane materials. In these applications, photopolymer technology is used to precisely define the microscopic openings in the membrane as it is being formed or to modify an existing membrane. Some of the applications of photopolymer chemistry to membranes include the modification of ultrafiltration membranes (78) and the manufacture of amphiphilic (79), gas permeable (80), untrafiltration (81), ion-selective electrode (82) and reverse osmosis membranes. 

Direct determination of surfactants in complex matrices can also be carried out using ion-selective electrodes. Depending on the membranes and additives used, the detergent electrodes are optimized for the detection of anionic surfactants [81], cationic surfactants [82], and even nonionic surfactants [83]. The devices are sensitive to the respective group of surfactants but normally do not exhibit sufficient stability and reproducibility for their use in household appliances. With further optimization of membrane materials, plasticizers and measurement technology, surfactant-selective electrodes offer high potential for future applications. 

The second edition of Ion-Selective Electrodes contains a survey of the theory and applications of ion-selective electrodes based on the literature published up to mid-1981. Because of the rapid progress in the whole field and the very large amount of diverse data, a compact and unified treatment of the theory has been attempted. The technology and the applications have also been updated. In view of these facts we have had to write practically a new book. In contrast to the first edition, only a selective list of references could be included in the book, because otherwise we would have to deal with more than four thousand references. 

Chapters 1 to 5 deal with ionophore-based potentiometric sensors or ion-selective electrodes (ISEs). Chapters 6 to 11 cover voltammetric sensors and biosensors and their various applications. The third section (Chapter 12) is dedicated to gas analysis. Chapters 13 to 17 deal with enzyme based sensors. Chapters 18 to 22 are dedicated to immuno-sensors and genosensors. Chapters 23 to 29 cover thick and thin film based sensors and the final section (Chapters 30 to 38) is focused on novel trends in electrochemical sensor technologies based on electronic tongues, micro and nanotechnologies, nanomaterials, etc. 

Among the various possibilities that offer the EC detection, ampe-rometry and conductimetry are, in this order, the most common. Although potentiometry results are a very interesting technique in many fields of Analytical Chemistry, it has not found enough echo in the microchip technology. Its incursion in microchips is related with the employment of ion-selective electrodes for Ba2+ determination [55] or potentiometric titration of iron ferrocyanide [56], but it has not yet been associated with CE microchips. 

Cobaltacarboranes also have been used in sensor technology. The sandwich complex [Co(B9C2Hu)2] can be used as a hpophilic coreceptor instead of tetraarylborate ion additives in ion selective electrodes, producing electrodes that are more selective for specific alkah metal ions. ... 

Bowers GN Jr, Brassad C, Sena SR Measurement of ionized calcium in serum with ion-selective electrodes a mature technology that can meet the daily service needs. Clin Chem 1986 32 1437-44. 

Since ion selective electrodes are dealt with quite extensively in this volume they will only briefly be mentioned here. They represent the most advanced field of sensor application in clinical routine diagnosis. A huge number of publications [7] and a variety of very successfully performing devices in the market reflect the mature state of this technology. 

Many modern analyzers u.se a closed-tube technology to minimize exposure to biohazards and to reduce manual manipulations. Samples and reagents arc dispensed automatically, the measurements made by photometry or ion-selective electrodes, and the results computed. Most have bar-coding capabilities to reduce errors from incorrect patient identification, A typical chemistry-immunochemisiry automated analyzer is shown in Figure 3.3-18. 

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