Electrochemical detection principle

Photometric. Amperometric. Fluorometric. Electrochemical detection principles. 

The combination of the electrochemical detection principle and the recycling of the analyte can be performed as is illustrated in Fig. 5, the bienzymatic system possessing the potential of the highest amplification rate [14]. 

The reduction of dimensions also reduces volumes which are accessible to the detector. Thus, detection principles related to geometric dimensions of the detector cell ai e not ideally suited for coupling to microsystems, whereas surface sensitive principles, such as electrochemical methods or optical methods utilizing the evanescent field of a waveguide, or methods which can be focussed on a small amount of liquid, such as electrochemiluminescence (ECE), ai e better suited. This is why electrochemiluminescence detectors ai e combined to microsystems. Moreover ECE has found wide applications in biochemistry because of its high sensitivity, relatively simplicity and feasibility under mild conditions. 

Flow injection analysis (F1A). In this technique, introduced by Ruzicka and Hansen, a small amount of sample is injected into a liquid flow (see Fig. 5.16), which apart from being automated is normally continuous, but can include the use of stopped-flow, merging zones extraction techniques in addition to FIA scanning and methods based on intermittent pumping89. The principles of FIA and the versions just mentioned will now be briefly discussed on the basis of the excellent review of Ruzicka and Hansen89 in order to understand the appli-cational possibilities of electrochemical detection in this technique. 

This chapter first describes the basic principles of electrochemical detection and then goes on to explain some aspects of turning these principles into practice. 

In Basic Principles of Electrochemical Detection it was simply stated that the electrode potential has to be changed for electrochemical detection. This is easier said than done. 

Many published articles on HPLC-ECD refer to the use of one of three voltammetric detectors (amperometric, coulometric, or polarographic). More detailed information on principles and techniques of various electrochemical detection modes can be obtained from the recent book, Coulometric Electrode Array Detectors for HPLC (34). There are also two electrode array detectors, the coulometric electrode array system and the CoulArray detector, currently available. Both detectors offer the qualitative data of PDA and the extreme sensitivity of ECD (34). The... 

Laser-induced fluorescence (LIF) has also been utilized as a highly sensitive detection principle for CE [48-51]. However, while the LIF detector is now able to achieve zeptomole (10 21) detection limits, conventional derivatization techniques are inefficient at these exceptional levels [52]. Also, CE has successfully been coupled with mass spectrometry (MS) [53], nuclear magnetic resonance (NMR) [54, 55], near-infrared fluorescence (NIRF) [56, 57], radiometric [58], flame photometric [59], absorption imaging [60], and electrochemical (conductivity, amperometric, and potentiometry) [61-63] detectors. A general overview of the main detection methods is shown is Table 1 [64]. 

Liess, M. and Steffes, H. (2000) The modulation of thermoelectric power by chemisorption a new detection principle for microchip chemical sensors. /. Electrochem. Soc. 147, 3151-3153. Tran-Minh, C. and Vallin, D. (1978) Anal. Chem. 50, 1874. 

Park J-W, Cundy KC, Ames BN (1989) Detection of DNA adducts by high-performance liquid chromatography with electrochemical detection. Carcinogenesis 10 827-832 Patterson LK (1987) Instrumentation for measurement of transient behavior in radiation chemistry. In Farhataziz, Rodgers MAJ (eds) Radiation chemistry. Principles and applications. Verlag Che-mie, Weinheim, pp 65-96... 

Fig. 17.4. Operation principles of a biosensor based on enzymatic oxidation of monophenol and/or o-diphenol by PPO and electrochemical detection by determining molecular oxygen or the oxidation product derived from monophenol and/or o-diphenol.

Principles of microfluidic ELISAs with electrochemical detection... 

Mobile phases useful for suppressed conductivity detection of anions include sodium hydroxide, potassium hydroxide, and the sodium and potassium salts of weak acids such as boric acid. In nonsuppressed conductivity detection, the ionic components of the mobile phase are chosen so that their conductivities are as different from the conductivity of the analyte as possible. Large ions with poor mobility are often chosen, and borate-gluconate is popular. For cations, dilute solutions of a strong acid are often used for nonsuppressed conductivity detection. For more information on the application of electrochemical detection to inorganic analysis, see Ion Chromatography Principles and Applications by Haddad and Jackson,17 which provides a comprehensive listing of the sample types, analytes, sample pretreatments, columns, and mobile phases that have been used with electrochemical detection. 

We will begin with a description of electrochemical sensors or more specifically composition sensors based on electrochemical principles (i.e., we refer to an electrochemical detection of composition). Another group of applications refers to devices in which the transference of mass and charge is used primarily to change composition or produce chemicals (electrochemical pumps and electrochemical reactors, or electrochemical filters) we will term such devices composition actors. At the end we will discuss energy conversion and storage devices (which we do not subsume under the term composition actors as here the energy aspect is to the fore). 

In conclusion, we have tried to present the principles of LCEC, describe the present applications that have been made, and survey the areas of potential utility by reviewing pertinent chemistry and related methods. It is our opinion that the success of LCEC in neurochemistry can carry over to pesticides owing not only to the advantages of electrochemical detection but also to the tremendous potential of its adjunct, liquid chromatography. 

Shoup, R. E. Bruntlett, C. S. Bratin, K. Kissinger, P. T. "Principles and Applications of Liquid Chromatography with Electrochemical Detection" Bioanalytical Systems, Inc. 

---