Detector technology

Thin-layer chromatography (TLC) is used both for characterization of alcohol sulfates and alcohol ether sulfates and for their analysis in mixtures. This technique, combined with the use of scanning densitometers, is a quantitative analytical method. TLC is preferred to HPLC in this case as anionic surfactants do not contain strong chromophores and the refractive index detector is of low sensitivity and not suitable for gradient elution. A recent development in HPLC detector technology, the evaporative light-scattering detector, will probably overcome these sensitivity problems. 

The miniaturized Mossbauer instruments have proven as part of the NASA Mars Exploration Rover 2003 mission that Mossbauer spectroscopy is a powerful tool for planetary exploration, including our planet Earth. For the advanced model of MIMOS II, the new detector technologies and electronic components increase sensitivity and performance significantly. In combination with the high-energy resolution of the SDD, it will be possible to perform XRF analysis in parallel to Mossbauer spectroscopy. In addition to the Fe-mineralogy, information on the sample s elemental composition will be obtained. 

Because of the underlying photophysics, fluorescence lifetimes are intrinsically short, usually on the order of a few nanoseconds. Detection systems with a high timing resolution are thus required to resolve and quantify the fluorescence decays. Developments in electronics and detector technology have resulted in sophisticated and easy to use equipment with a high time resolution. Fluorescence lifetime spectroscopy has become a popular tool in the past decades, and reliable commercial instrumentation is readily available. 

For reference methods, HPLC with various detectors has become the standard reference technique for analysis of food additives, but new developments in this area are mainly linked to detector technology. Diode array detectors have not totally met the expectations of food analysts in terms of their specificity and LC-MS is likely to fill the gap. Specific detection with biosensor chips may also have a future for certain analyses. The use of combined LC-MS/DAD systems is... 

Fluorescence spectroscopy and its applications to the physical and life sciences have evolved rapidly during the past decade. The increased interest in fluorescence appears to be due to advances in time resolution, methods of data analysis and improved instrumentation. With these advances, it is now practical to perform time-resolved measurements with enough resolution to compare the results with the structural and dynamic features of macromolecules, to probe the structures of proteins, membranes, and nucleic acids, and to acquire two-dimensional microscopic images of chemical or protein distributions in cell cultures. Advances in laser and detector technology have also resulted in renewed interest in fluorescence for clinical and analytical chemistry. 

Average Data File Size based on Detector Technology... 

FIGURE 9 The impact of detector technology on data file size. 

X-ray topography is the X-ray analogue of transmission election microscopy and as such provides a map of the strain distribution in a crystal. The theory of image formation is well established and image simulation is thus a powerful means of defect identification. Despite a reputation for being a slow and exacting technique, with modem detector technology and care to match spatial resolution of detector and experiment, it can be a powerful and economical quality-control tool for the semiconductor industry. 

This section is focused primarily on source and detector technologies. For some applications the source or the detector actually defines the entire measurement technology, for example tunable lasers (source) and array spectrographs (detector). There are other important technologies to consider, especially in the area of data acquisition, control, computer, and commuiucation technologies. These are rapidly changing areas, and if viewed genericaUy, service all forms of instrumentation. Where practical, compaiues tend to use standard platforms, but for certain applications, where performance is critical, there is still a case for proprietary solutions. 

Certain factors are likely to influence future analyses of more complex viruses. Crystal stability is governed by packing interactions and, as can be seen from Fig. 16.4, is, to a first approximation, inversely proportional to the square of the virus radius, presumably underl)dng the problems with crystal stability for analyses such as that of PRDl. Even assuming that well-ordered, stable crystals can be formed, technical considerations will place an upper limit on the unit cell size from which useful data can be collected. Nevertheless, with some improvements in beam and detector technology, we expect that data collection from cells up to 2000 A should be feasible for even a primitive unit cell. 

In spite of recent advances in detector technology, metal detectors, mine probes, and canines remain as the most widely utilized mine detection tools. All of these methods have been utilized with some success, but all have limitations. For example, metal detectors must be operated at extremely high gain settings to obtain adequate sensitivity to detect low-metal-content mines. This is an issue because minefields are often littered with metallic objects (e.g., fragments from exploded munitions). Hence, false alarms are common, limiting the utility... 

With the more widespread use of subnitrogen cryogenic temperatures, use of smaller samples made possible by brighter sources, and rapid developments in detector technology and computational methods, the conclusions of the oxalic acid project are now of mainly historical importance. However, the project remains an example of the value of collaborative efforts in establishing the validity of a scientific method. 

In the next section, the term "complex polymers" is defined, the effects of polymer complexity on conventional SEC analysis are examined, and attempts to analyze ccanplex polymers by utilizing SEC detector technology are summarized. High performance liquid chromatography (HPLC) attempts to accomplish the task are then described. This is followed by a summary of the theoretical development of OC, experimental results of OC analysis, complications which emerged, and finally a summary of the status of OC in light of recent developments. (1) and (2) provide reviews of OC. 

Attenpts to Analyze Complex Polymers Using SEC Detector Technology. For linear copolymers, multiple detectors and, more recently, diode array UV/vis spectrophotometers have been used in attempts to overccxne the above analysis problems. The basic idea is to provide more than one detector response so that the polymer concentration and the number of properties will together equal the number of detector responses (Figure 4). This provides the same number of equations as the number of unitnowns (5,6). 

Detector Technology. For copolymer composition analysis the new diode array UV/vis detectors are extremely attractive the absorption at many wavelengths are instantaneously recorded there is only a single spectrophotometer cell so that transport time delays between detectors and axial mixing in detector cells do not confound comparison of detector response at different wavelengths and for styrene copolymers, extremely low concentrations of polymer can be detected. 

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