Detector electrode systems types

The detector cell was a three-electrode system consisting of a flow-through nickel working electrode, a saturated calomel reference electrode (SCE), and a stainless steel outlet tubing counter electrode. The tubular-type electrode cell housing was constructed of molded Teflon, which was machined to provide the channels and to accommodate the fittings. The working electrode area was... 

The design of both types of detector systems has been reviewed in detail elsewhere (Kissinger, 1977). The following discussion will concentrate on ways of obtaining maximum efficiency from commercially available systems (list of suppliers at the end of the chapter), although it is a relatively simple project to build an electrode and detector/amplifier system based on published information (e.g., Kissinger et a/., 1973 Keller et al, 1976). 

At present the ESA Coulochem is the only commercially available coulometric detector. Several different types of cell are now available, most of which contain two analytical electrodes in series. The standard cell (Model 5010) contains equal sized PGEs, but in the high sensitivity cell (Model 5011) the surface area of the second electrode is reduced with the aim of producing a better S/N ratio. Despite the argument that the increased surface area available in PGE systems only increases the noise in proportion to the increased signal," such systems do appear to give an enhanced S/N ratio in certain applications, as compared to glassy carbon electrodes in thin-layer or wall-jet assemblies, and may offer more flexibility in routine use. Even better S/N ratios are claimed for the Model 5014 cell, which has been developed specifically for use with microdialysis samples. 

The carrier stream is merged with a reagent stream to obtain a chemical reaction between the sample and the reagent. The total stream then flows through a detector (Fig. 1.1 (b)). Although spectrophotometry is the commonly used detector system in this application, other types of detectors have been used, namely fluorometric, atomic absorption emission spectroscopy and electrochemical, e.g. ion selective electrodes. 

Arrays can be divided into three groups depending on their design (Fig. 32.2). In the first design, each electrode is independently addressed (Fig. 32.2a). This type of array allows several practical applications. On one hand, these devices can be fabricated for obtaining the same information at different sites of a medium. For example, studies about the responses of neuronal cell cultures under different stimulus [85-87]. On the other hand, these devices can be designed to obtain different information at reduced spaces, i.e. multianalyte determination. Those arrays can be employed directly like detectors in flow systems [88] (where each electrode is maintained at a different potential) or they can be individually modified for specific analytes [89],... 

A few other types of anion sensors have been mentioned recently in the literature. Tetrathiofulvalene microcrystals immobilised at a platinum electrode displayed electrochemical properties that were affected by the presence of anions in solution, with some selectivity for anions such as bromide [ 145]. A flow-injection analysis system using anion-exchange columns for separation and polyaniline electrodes as detectors could detect dichromate down to 0.004 ppb and could be used for seawater samples [146]. 

When designing biosensors, it is essential to study and tmderstand each component that constitutes this complex system as well as aU the factors that influence its unique performance and limitations [5,6]. Despite an important number of publications in the biosensor field, several aspects require further optimization and improvements many of these could be related to inadequate materials and insufiftcient understanding of the underlining mechanism. Since the properties and the type of the material used are largely connected with the transducer and the transducer/detector interface, a considerable attention must be paid to the nature of electrode material. The rapid... 

The combination of chemical and biological sensors with flow injection has been demonstrated. Both more-traditional-type sensors such as pH electrodes and newer sensors such as fiber optics and surface acoustic wave detectors have been incorporated into FIA systems with success. An advantage that FIA brings to the sensor field is the possibility of turning a moderately selective sensor into a selective sensor by incorporating into the FIA system some type of selectivity enhancement technique such as gas diffusion, dialysis, and reactors. Finally the FIA systems permit renewable systems since sensor surfaces and reaction cells can be washed, surface regenerated, and reagents replenished on demand. 

Spectroelectrochemistry [99] Is a hybrid technique resulting from the association of electrochemistry with spectroscopy via the use of cells with optically transparent electrodes [100-103]. The potential of this technique lies in the possibility of Identifying both the type and the amount of the species generated In an electrochemical step. The Intrinsic characteristics of spectroelectrochemistry require the use of fast measuring systems —spectroscopic image detectors in most cases [104-107]— and the consequent acquisition of the large number of data provided by the detection system In a short time by means of an oscilloscope or, even better, of a computer also allowing the subsequent exhaustive treatment of the raw data. 

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