Detectors improvement

A later General Electric x-ray photometer26 is noteworthy because it uses current ionization chambers (2.6) as detectors. Improved means of external amplification made it possible to use this type of detector in a satisfactory photometer with the simple circuit shown in Figure 3-9. 

A. Metal Oxide Phases IMPROVEMENTS IN DETECTORS IMPROVEMENTS IN HPLC THROUGHPUT... 

Simplifying Sample Preparation New Column Technologies Improvements in Detectors Improvements in HPLC Throughput... 

The separation of selenium species by HPLC followed by either AAS or ICP-OES detection has been studied. When the column effluent has been connected directly to the nebuliser of the detector, the detection limits have not been adequate for analysis of environmental samples. The introduction of volatile derivatives such as hydrides to the detector improves the detection limits since a larger proportion of the analyte is transported to the detector. The reduction technique was applied to the determination to selenium species in seawater (Cobo-Fernandez et al., 1993). The analyses were carried out on-line using FI. The equipment included a reaction loop tested at 140°C for the reduction of Se to Se. Se was calculated as the difference between total selenium and original Se (determined without heating). The detection limit was 0.7 mg dm-3 for each species. 

Even assuming that these limitations are acceptable, the most appropriate and promising techniques for security applications are based on nanosecond neutron analysis (not only in API) therefore, the use of HPGe with its intrinsically slow signal (timing resolutions of tens of nanoseconds at best) and low-rate capability is highly undesirable. The use of HPGe in this application with 14-MeV neutron sources has been described in the literature for more than 15 years with little evidence that such detectors improve real-world system performance and much evidence that they do not. 

New Razor detector improves resolution, mass accuracy,... 

On the basis of the diversity of applications presented in this chapter, it becomes clear that CE has found a niche among separation techniques for environmental analysis. Future directions will likely include refinement of preconcentration strategies and further detector improvements to achieve the desirable low-concentration limits of detection. In addition, with the consolidation of CE-MS technology, more robust methods are likely to emerge with enhanced sensitivity and superior selectivity, improving further the acceptance of CE in the routine determination of pollutants in real samples. 

FIGURE 27.14 SPECT system configurations. Although a single scintillation camera can be used to acquire SPECT data, multiple detectors improve the overall sensitivity. Two detectors arranged at either ISO or 90° are the most common configuration. 

A second obvious area of application is in continuous flow analysis or flow injection analysis systems, in which the immobilized molecules form reactors that can be readily inserted and replaced in a flow analysis manifold. The physical form of the enzymes varies widely packed-bed reactors are often used, but open-tube wall reactors and membrane reactors have also been investigated. A principal advantage of all such systems is that they can use all the optical or electrochemical detectors routinely used in flow analysis. However, the problems of producing stable and robust immobilized enzyme reactors have proved more intractable than many researchers hoped, and other advances (e.g.. the use of more sensitive detectors, improved availability of low-cost soluble enzymes) have minimized the advantages of using solid phase enzymes. 

Eventually, as multichannel detectors improved and the spectrographs were redesigned to take advantage of the new possibilities, these new designs were incorporated into newer Raman microprobes. Some of these new systems also incorporated the concepts of con-focality in both microprobing and imaging. Because of the importance of confocality, it will be treated in more detail below. 

Finally, nanotechnology can for sure provide novel microfluidic solutions for food applications still to be explored. It can be used in pumping and flow devices but nanomaterials are already also employed as detectors, improving analytic performance and opening new avenues for future implementation of applications in the field of food analysis. 

Recent advances in far I.R. instrumentation have been mainly in the area of detector improvement. Detection in the far I.R, is restricted to bolometric detection as opposed to the availability of photo conductive detection at wavelengths shorter than about 30 pm. An early standard for far I.R. detectors was the Golay bolometer detector. The periodic heating and cooling of a chopped I.R. beam is translated into expansion contraction of a small pocket of gas which in turn deflects a membrane. The membrane deflection is measured electro-optically and converted to the corresponding signal. 

Multichannel dispersive IR instruments utilize a multichannel detector (Fig. 3.2). A multichannel detector is an array of many detector elements. Using a multichannel detector improves the signal-to-noise ratio proportional to the square root of the number of detector elements. The use of a multichannel detector has improved the performance of near IR instrumentation. 

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