Conductimetric sensor

Keywords Langmuir-Blodgett film, pH sensors, conductimetric sensors, polypyrrole. 

A poly(aniline boronic acid)-based conductimetric sensor for dopamine consisting of an interdigitated microarray electrode coated with poly(aniline boronic acid) has also been developed by the Fabre team. The sensor was found to show a reversible chemoresistive response to dopamine without interference by ascorbic acid from their mixtures.42... 

Figure 1.11 — Average number of papers on (bio)chemical sensors published annually, based on data from Janata s biannual review. E electrochemical sensors ISEs ion-selective electrodes P potentiometric sensors A amperometric sensors C conductimetric sensors O optical sensors M mass sensors T thermal sensors. (Adapted from [23] with permission of the American Chemical Society).

Severinghaus electrodes have found wide application in clinical analysis. It is pertinent to mention here that the general principle of permeation of the gas through a hydrophobic membrane followed by its detection (with or without its solvolysis) has been used with different types of internal sensors, for example, optical, ampero-metric, conductimetric, or a mass sensor. The choice of the internal sensing element depends on the circumstances of the application in which the gas sensor would be used, such as the required time response, selectivity considerations, complexity of instrumentation, and so on. 

Atrazine in solution Methacrylic acid (MAA) or DEAEM M IP-based conductimetric sensor 0.01 mg/L Piletsky et al., 1995... 

Arnold FH, Zheng W, Michaels AS. A membrane-moderated, conductimetric sensor for the detection and measurement of specific organic solutes in aqueous solutions. Journal of Membrane Science 2000, 167, 227-239. 

For gas sensing devices the conductimetric measuring principle is used in most cases with good success (see section on gas sensor systems). However, for practical applications and commercialization much more investigations are still needed. 

Conductimetric sensors - electrochemical sensors for which the electrical - conductivity of the sensor material is recorded. A typical example is the so-called - Taguchi sensor that is used for detection of reducing gases in air. Ref [i] Janata / (1989) Principles ofchemical sensors. Plenum, New York... 

An enzyme biosensor consists of an enzyme as a biological sensing element and a transducer, which may be amperometric, potentiometric, conductimetric, optical, calorimetric, etc. Enzyme biosensors have been applied to detecting various substrates (Table 3.1), which are selectively oxidized or reduced in enzyme-catalyzed processes depending on the nature of substrates and enzymes used (oxidases or reductases) to construct sensors. 

During the last decade the number of application of MIP-based sensors has increased dramatically. The high selectivity and affinity of MIPs for target analytes make them ideal recognition elements in the development of sensors. Capacitive (Panasyuk etal., 2001), conductimetric (Piletsky et al., 1995), field effect (Lahav et al., 2004), amper-ometric (Kritz and Mosbach, 1995), and voltammetric (Pizzariello et al., 2001), electrochemical transduction systems have been used. Sensors based on conductimetric transduction have been developed by Piletsky et al. (1995) for the analysis of herbicides. A system using a TiC>2 sol-gel system, and with a linear range of 0.01-0.50 mg L-1 for atrazine, without interference of simazine, and chloroaromatic acids has been described by Lahav et al. (2004). 

Trichloroacetic acid and haloacetic acids 4-VP+EDMA Conductimetric sensor 5... 

Capacitance-based chemical sensors are in the class of devices that transduce analytes into electrical currents. Such sensors are typically comprised of a dielectric, chemically-sensitive film coated onto a substrate electrode these films pass low conduction current, making amperometric or conductimetric measurements less sensitive or attractive for signal transduction. To detect an analyte, changes in the chemically-sensitive film s capacitive properties (associated with its dielectric constant, charge uptake, or formation of interface dipole layers) are measured when an active species is present or generated. 

There are many applications for conductimetric measurements, some of which are very specific. For example, in a medical application, a conductivity sensor has been used to determine levels of ammonia in human breath In the same article, the authors also demonstrated a second sensor for breath analysis of carbon dioxide. In environmental analysis, a samarium iron oxide (SmFeOs) gas sensor has been developed for the detection of ozone based on conductance at sub-ppm levels ". ... 

Sergeyeva T, Piletsl S, Brovko A et al. Selective recognition of atrazine by molecularly imprinted polymer membranes. Development of conductimetric sensor for herbicides detection. Anal Chim... 

Bavastrello V., Stura E., Carrara S., Erokhin V., and Nicolini C., Poly(2,5-dimethylaniline)-MWNTs nanocomposite A new material for conductimetric acid vapours sensor. Sens. Actuators B, 98, 247-253, 2004. 

Several methods are used to determine sensor response (S) in the literature, particularly in regard to conductimetric gas sensing, where the ratio of the test response to a control response is determined. The method used typically depends on whether the test response results in a signal that is either greater or lesser than some control value. To avoid confusion and allow standardization, five measures of S are used in this table, denoted Si-Ss- In some publications, these values are further multiplied by 100 to yield a percentage response. However, in this work, all percentage values have been divided by 100 to yield the response quotient. 

Electrochemical sensor fabrication has dominated the analytical application of polymers. In some sensors the polymer film acts as a membrane for the preconcentration of ions or elements before electrochemical detection. Polymers also serve as materials for electrode modification that lower the potential for detecting analytes. In addition, some polymer films function as electrocatalytic surfaces. Using a polymer in biosensors is a very rapidly developing area of electroanalytical chemistry. Polymeric matrix modifiers have been applied as diffusional barriers in constructing not only sensitive amperometric biosensors, but also electrochemical sensors that apply potentiometric, conductimetric, optical, and gas-sensing transducer systems. The principles, operations, and application of potentiometric, conductimetric, optical and gas sensors are described in Refs. 13, 39-41. In this chapter, we focus mainly on amperometric biosensors based on redox enzymes. 

Focused on the electrochemical applications used to design sensors for ionic, molecular or gas species. Targeted at BA level and master s degree students, as well as students at engineering school, it is also adapted to selftraining. This book provides a recap of the basic concepts, before then applying them to different types of transduction (amperometric, conductimetric and potentiometric sensors). There is also a selection of problems to solve with the corrections provided. 

Because EPs can be formed and modified electrochemically their application to electrochemical sensors is the natural choice. It is again the remarkable flexibility of their design which makes them universally applicable if necessary they can be prepared with the high conductivity needed for amperometric sensors. They also form well defined ohmic contacts with the metal electrodes required for conductimetric sensors. Their thickness, which is important in potentiometric sensors, can be controlled. We now take a more detail look at the three principal transduction electrochemical modes. A good source of information on electrochemical aspects of EPs is the review chapter on chemically modified electrodes by Murray [3]. 

Conductivity is undoubtedly the most closely investigated physical parameter of EPs. It is heavily dependent on the level of the primary doping, i.e. on the concentration of the counterion. Addition of another type of electroactive molecule to the polymer can be viewed as a secondary doping and, as expected, it also affects the conductivity of the EP, albeit usually less than the primary doping. Nevertheless, this incremental change of conductivity is the basis for operation of conductimetric chemical sensors, better known as chemiresistors. 

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