Detection principles

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. 

Fig. 14-3. NOj chemiluminescent detection principle based on the reaction of NO with O3.

Individual types of electrical apparatus, of course, require protective schemes that are specifically applicable to the problem at hand. There are, however, common detection principles, relaying designs and devices that apply to all. 

The Instrumentation and Control Fundamentals Handbook was developed to assist nuclear facility operating contractors provide operators, maintenance personnel, and the technical staff with the necessary fundamentals training to ensure a basic understanding of instrumentation and control systems. The handbook includes information on temperature, pressure, flow, and level detection systems position indication systems process control systems and radiation detection principles. This information will provide personnel with an understanding of the basic operation of various types of DOE nuclear facility instrumentation and control systems. 

In addition, typical methods of sensing are total internal reflection fluorescence or monitoring of fluorescence resonance energy transfer6,7. The second class is a direct optical detection principle which relies either on reflectometry or refractometry. The latter is connected to evanescent field... 

Interferometric sensors frequently have also been applied to biosensor measurements. Thereby, the evanescent field technique (Mach-Zehnder interferometer) has been compared with other optical detection principles regarding information on layer structure and in case of biosensing30. The... 

FIGURE 2.2 Enzymatic formation of thiocholine and detection principles for pesticide. 

FIGURE 17.3 Scheme of the detection principle of antioxidant activity using a cytochrome c functionalized gold electrode. A0I is the antioxidant under investigation. (From [213], with permission.)... 

An array or a matrix of nucleic acid probes immobilized at discrete locations on a silicon or glass surface provides a convenient means to simultaneously probe a sample for the presence of many different target sequences. Microarray biochip scanning devices, mostly based on fluorescent labels, are now currently available, and could also be used with CL labels to take advantage of the higher sensitivity of this detection principle. 

A. G. Marshall and C. L. Hendrickson. Fourier Transform Ion Cyclotron Resonance Detection Principles and Experimental Configurations. Int. J. Mass Spectrom., 215(2002) 59-75. 

A radioactivity detector is used to measure radioactivity in the HPLC eluent, using a flow cell. The detection principle is based on liquid scintillation technology to detect phosphors caused by radiation, though a solid-state scintillator is often used around the flow cell [17,31]. This detector is very specific and can be extremely sensitive. It is often used for conducting experiments using tritium or C-14 radiolabeled compounds in toxicological, metabolic, or degradation studies. 

The Signal Detection principle is a determination of the relationship between hits and false alarms. In determining signal detectability, a stimulus or a few stimuli are presented in random order, alternating with noise. Since sensory impressions resulting from the presentation of stimulus versus noise are assumed to be normally distributed over the same intensity continuum and to have the same dispersion, the index of detectability d for p (hits) minus p (false) indicates the extent to which the two distributions overlap. 

The analytical exploitation of the full dynamic range of a detection principle invariably encompasses nonlinear portion of the concentration response function. The use of cubic spline functions for the description of this relationship is discussed after a short introduction to the theoretical principles of spline approximations. 

Separation by HPLC typically falls into one of six categories chiral, ion exchange, ion pair, normal phase, reversed phase, or size exclusion. Reversed phase is the most common type employed, and although various detection principles can be used in HPLC, UV is the most typical. 

Stalberg, O., Westerlund, D., Rodby, U. B., and Schmidt, S. (1995). Determination of impurities in remoxipride by capillary electrophoresis using UV-detection and LIF-detection — principles to handle sample overloading effects. Chromatographia 41, 287—294. 

The analytic principles that have been applied to accumulate air quality data are colorimetry, amperometry, chemiluminescence, and ultraviolet absorption. Calorimetric and amperometric continuous analyzers that use wet chemical techniques (reagent solutions) have been in use as ambient-air monitors for many years. Chemiluminescent analyzers, which measure the amount of chemiluminescence produced when ozone reacts with a gas or solid, were developed to provide a specific and sensitive analysis for ozone and have also been field-tested. Ultraviolet-absorption analyzers are based on a physical detection principle, the absorption of ultraviolet radiation by a substance. They do not use chemical reagents, gases, or solids in their operation and have only recently been field-tested. Ultraviolet-absorption analyzers are ideal as transfer standards, but, as discussed earlier, they have limitations as air monitors, because aerosols, mercury vapor, and some hydrocarbons could, interfere with the accuracy of ozone measurements made in polluted air. 

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