Multiple detectors, types

Such effects principally cannot be observed in multi band detectors such as a UV diode array detector or a Fourier transform infrared (FTIR) detector because all wavelengths are measured under the same geometry. For all other types of detectors, in principle, it is not possible to totally remove these effects of the laminar flow. Experiments and theoretical calculations show (8) that these disturbances can only be diminished by lowering the concentration gradient per volume unit in the effluent, which means that larger column diameters are essential for multiple detection or that narrow-bore columns are unsuitable for detector combinations. Disregarding these limitations can lead to serious misinterpretations of GPC results of multiple detector measurements. Such effects are a justification for thick columns of 8-10 mm diameter. 

Detector Type U, Th, Pa, Ra Semiconductor Single ion counter Multiple-Faraday + single or multiple-ion counters Single ion counter Multiple-Faraday + single or multiple-ion counters Single ion counter Multiple-Faraday + single or multiple-ion counters Multiple-Faraday + single ion counter... 

There are many types of HPLC detectors available today with the most popular ones including UV and UV-photodiode array (PDA), fluorescence, refractive index, evaporative light scattering (ELSD), charged aerosol (CAD), and the mass spectrometer. Of these, the most commonly used detector for pharmaceutical analytical methods is the UV detector since a majority of pharmaceutical compounds have some type of chromophore. Multiple detectors in series can also be utilized in order to obtain more information per chromatographic run. For example, a PDA detector can... 

Besides the universal detector systems, for example electron capture, flame ionisation and thermal conductivity usually coupled with gas chromatographic columns, various other detectors are now being used to provide specific information. For example, the gas chromatograph/mass spectrometer couple has been used for structure elucidation of the separated fractions. The mechanics of this hybrid technique have been described by Message (1984). Other techniques used to detect the metal and/or metalloid constituents include inductively coupled plasma spectrometry and atomic absorption spectrometry. Ebdon et al. (1986) have reviewed this mode of application. The type and mode of combination of the detectors depend on the ingenuity of the investigator. Krull and Driscoll (1984) have reviewed the use of multiple detectors in gas chromatography. 

Figure 3.5 An example of XRF measuremenf geomefry. A basic measuremenf geomefry where an f f. 1 GBq tiAm source (A) and an HPGe defecfor (B) are assembled in fixed posifions relafive fo each other and focused onto a point. Both source and detector are shielded and collimated with lead. The other equipment options may involve multiple sources or an X-ray tube and another detector type.

In the case of copolymers, any single detection method will have variable sensitivity for each type of mer. If the copolymer composition is itself a variable, then the use of dual or even multiple detectors will be required for accurate results. Calibrations for both homopolymers should be followed, if possible, by an analysis of homopolymers of similar molecular weights, before attempting an analysis of the copolymers themselves. 

Instruments of this type typically have two levels of alarm 20% LFL and 60% LFL. If multiple detectors are installed in a single location, then a voting system can be installed. For example, if just one 20% alarm sounds, then all hot work must stop but other work can continue as normal. If three 20% alarms or one 60% alarm sounds, then an emergency response is called for. 

System volume is one of the parameters that instrument manufacturers have striven to reduce when the engineering of UHPLC systems began. Some reductions were simple. In others, for instance, in autosamplers, the volume reduction was more complicated. For this reason, total system volumes are not uniform across all available instrumentation. Some manufacturers strictly define their system volume, and the qualification of the instruments for use in regulated environments hinges on this volume being fixed. Other manufacturers offer more flexible options. Virtually all UHPLC systems are modular and can have different components (column switcher vs. single column, binary pump vs. quaternary pump, multiple detectors), and for some manufacturers, two systems may have the same components but be plumbed differently. All of these configurations have an effect on the system volume. Because some of the benefits of UHPLC are the speed of analysis, sharpness of the peaks, and retention of resolution, extra dead volume is undesirable, as it reduces these benefits. To ease method transfer problems, one must account for these types of differences. 

The depth resolution of ERDA is mainly determined by the energy resolution of the detector system, the scattering geometry, and the type of projectiles and recoils. The depth resolution also depends on the depth analyzed, because of energy straggling and multiple scattering. The relative importance of different contributions to the depth resolution were studied for some specific ERDA arrangements [3.161, 3.163]. 

When dealing with an entire fire detection system that utilizes more than one type of detector, a Detonator Module greatly expands the flexibility and capability of the system. An individual Detonator Module can accept multiple inputs from UV and IR controllers, other Detonator Modules, manual alarm stations, heat sensors, smoke detectors or any contact closure device. In the event of a fire, any of these devices will cause the internal fire circuitry of the module to activate the detonator circuit, sound alarms, and identify the zone that detected the fire. When properly used, a Detonator Module will add only one millisecond to the total system response time. See Figure 8 for an illustration of a fire detection system with a Detonator Module. 

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