Accumulation amperometric sensor

In general, traditional electrode materials are substituted by electrode superstructures designed to facilitate a specific task. Thus, various modifiers have been attached to the electrode that lower the overall activation energy of the electron transfer for specific species, increase or decrease the mass transport, or selectively accumulate the analyte. These approaches are the key issues in the design of chemical selectivity of amperometric sensors. The long-term chemical and functional stability of the electrode, although important for chemical sensors as well, is typically focused on the use of modified electrodes in energy conversion devices. Examples of electroactive modifiers are shown in Table 7.2. 

Porphyrins are often employed in sensors on account of their ability to act as cation hosts and, with a suitable metal ion coordinated, as redox catalysts. Electropolymerised poly(metalloporphyrin)s have been used as potentiometric anion-selective electrodes [131] and as amperometric electrocatalytic sensors for many species including phenols [132], nitrous oxide [133] and oxygen [134]. Panasyuk et al. [135] have electropolymerised [nickel-(protoporphyrin IX)dimethylester] (Fig. 18.10) on glassy carbon in the presence of nitrobenzene in an attempt to prepare a nitrobenzene-selective amperometric sensor. Following extraction of the nitrobenzene the electrode was exposed to different species and cyclic voltammetric measurements made. A response was observed at the reduction potential of nitrobenzene (the polyporphyrin film acts only to accumulate the analyte and not in a catalytic fashion). Selectivity for nitrobenzene compared with w-nitroaniline and o-nitroto-luene was enhanced compared with an untreated electrode, while a glassy carbon-... 

There are two main types of amperometric sensors based on EPs. The first group uses the accumulation of the analyte inside the EP matrix in order to achieve a lower detection limit [56]. The second group are biosensors utilizing oxido-reductases immobilized in the EP. The idea is to facilitate the electron transfer between the redox centre(s) of the enzyme and the metal electrode. 

Potentiodynamic gas sensors have a schematic structure that is practically equal to that of amperometric gas sensors. They are -> electrochemical cells that measure a -> current signal directly related to the concentration of the analyte, but are not necessary operated in a region where -> mass transport is limiting. They are typically employed to detect less reactive species such as benzene and halogenated hydrocarbons that require a previous accumulation step at a suitable -> adsorption potential to be then reduced or oxidized according to a given potential scan [iii]. The adsorption time can be automat-... 

Ion-exchange polymers, redox polymers and especially electroconducting polymers have been utilised extensively in CMEs including CWEs, ISFETs, amperometric and conductometric sensors, both as selective accumulators and as... 

Electrochemistry works using the principles of oxidation-reduction reactions which generate electric currents or, more simply, the conversion of chemical information into an electrical signal. Electrochemical cells or sensors usually contain a working electrode, to which a potential is applied, and a reference electrode. The oxidation-reduction reaction that ensues is then recorded as an electric current which is a measurement of the analyte from the reaction. Electrochemical methods can be further subdivided into amperometric (measures current), potentiometric (measures potential), conductometric (measures the conductive properties of the medium), impedimetric (measures resistance and reactance) or field effect (measures current through charge accumulation at a gate electrode). ... 

---