Detection devices, natural

The selection of labelling need not affect the "blind" nature of the analysis since Q.C. samples do not have to be identified until analyses are completed. Treating the Q.C. samples in "blind" fashion is often important to ensure that they do not receive special treatment. These samples are used as surrogate replicates for real samples and are used to evaluate method performance in lieu of routine unknown sample replicates. Therefore, they must not receive special operator attention or handling. However, the "blind" requirement may be relaxed when sample preparation has been minimal or well controlled, or when automated instrument performance is the sole subject of scrutiny. It may be argued that "blind" labelling is unecessary even when the detection device is under human operator control since any attempt to "adjust" the determination of either Q.C. sample to match its pair mate will be expressed as an anomalous difference D. 

Numerous extensions may be envisaged, such as the introduction of various central cores, in particular those already known to yield molecular liquid crystals, the incorporation of light-sensitive or electro-sensitive units, the potential use for detection devices, and the extension to various recognition components of biological nature (for biomesogens see 9.109, 9.112, 9.115, 9.146). 

Analytical chemists have always admired the supersensitive natural detection devices built into organisms as part of elaborate control systems used... 

Analytical chemists have always admired the supersensitive natural detection devices built into organisms as part of elaborate control systems used to regulate the levels of various crucial chemicals, such as enzymes, hormones, and neurotransmitters. Be-... 

Colorimetric testing tubes may be used if a specific chemical agent is suspected (Figure 2.17). These tubes with their indicator will usually reveal the nature of the chemical agent and its level. It should be remembered that cross-reactions are common among chemical agents measured in this manner (see Practical Skills 5 for use of these detection devices). 

Deviation from the standard isotherm in the high-pressure region offers a means of detecting the occurrence of capillary condensation in the crevices l>etween the particles of a solid and in any mesopores present within the particles themselves. A convenient device for detecting deviations from the standard is the t-plot . In the next section the nature and uses of t-plots will be discussed, together with a,-plots, a later development from them. As will l>e shown, both of these plots may l>e used not only for the detection of capillary condensation in mesopores, but also for showing up the presence of micropores and evaluating their volume. 

A chemical microsensor can be defined as an extremely small device that detects components in gases or Hquids (52—55). Ideally, such a sensor generates a response which either varies with the nature or concentration of the material or is reversible for repeated cycles of exposure. Of the many types of microsensors that have been described (56), three are the most prominent the chemiresistor, the bulk-wave piezoelectric quartz crystal sensor, and the surface acoustic wave (saw) device (57). 

From the above-given condensed review of the EEP detection methods one can infer that none of these methods can independently satisfy all the requirements specified for the study of heterogeneous processes involving the EEP participation. To our opinion, the application of semiconductor sensors for detection of EEPs can be provided by a combination of required qualities. The sensors are highly sensitive, miniature, can be operated within wide ranges of gas temperatures and pressures, and are made of simple devices. At the same time, a series of problems arise connected with the preliminary preparation of sensors and improving their selectivity. These and other questions of general nature will be considered in the section that follows. 

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