Detection speed

Fig. 31. HPLC chromatogram of the mixture obtained when using Ratz s procedure for the synthesis of NjPsCMeAzlg (Waters Liquid Chromatograph Instrument, (t Bondapack Cie reverse phase, pure methanol, RI detection, speed rate = 1 cm/mn) A = NaPjfMeAzIg, B = N3P3(MeAz)sCl, C = NaPjCMeAzl Oj...

These analyzers are being used in incinerator stacks and other applications where samples are typically dirty or corrosive and high detection speeds are required. The incorporation of fiber-optic technology has provided a high degree of installation flexibility (Figure 3.38). 

Since the early 1980s, considerable research effort has been devoted to the development of fiber optic (FO) biosensors because their potential sensitivity, detection speed, and adaptability to a wide variety of assay conditions. The area of optical fibers biosensors is quite wide and numerous applications have been described in the literature, mainly via the evanescent wave detection [1,16—19]. A number of possibilities for FO sensing have been proposed and some of them have reached commercial development [1,16]. 

Once the chemical vapor comes into contact with the SAW sensors, a response is developed within seconds. A complete analysis cycle for a SAW-based detector includes sampling time, desorption time from the preconcentrator, analysis time by the sensors, and recovery time to clear the sorbed chemicals from the polymer. Additional elution time is added when a GC column is incorporated. Analysis time is only a very small portion of the entire cycle. Detection speed depends on sampling time, especially when a preconcentrator or GC column is used for low-concentration samples. While it is possible to bypass the preconcentrator to reduce the analysis cycle time, the probability of false responses by the sensors significantly increases. Recovery time depends on the quantity of chemicals sorbed, strength of the bond between the sorbed molecules and sorption polymer, and the temperature necessary for releasing sorbed chemicals. Recovery time ranges from a few seconds to several minutes. 

Optical detectors. Use or dispensing of pyrophoric materials, the materials which spontaneously react with air, cannot be monitored by conventional smoke or heat detectors. Their detection speed is simply too slow. Optical sensors for each application require judicious selection. (See Figs. 5 and 6.)... 

Factors such as stability, detection speed, recovery time, frequency and methods of calibration, required maintenance, and reliability can also influence the selection of a specific gasdetection technology. 

Detection Speed. Detection speeds can differ between various gas detection technologies and may significantly contribute to the overall response time of atoxic gas monitoring system. The selection of a specific gas detection technology can have a major impact if instantaneous response times are required. 

The main time delays occur by the limited response speed of a cantilever and the z-scanner, the detection speed of cantilever oscillation amplitude, and the parachuting time. Here, we briefly describe various techniques to shorten these time delays. 

FTIR has also been applied to detect many compounds (Pielesz 1999). The infrared sensing is a powerful tool in the detection of organic species in aqueous solutions due to the detection speed and the abundant chemical information obtained. This... 

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