Multiple Detection Systems

Unlike Coulochem detectors (Section 5) in which the electrodes are arranged in series, amperometric detectors, containing two or more electrodes, can be used either in parallel or in series. In the first approach, the eluate simultaneously passes over two electrodes, which can be held at different working potentials. The benefits of this approach are that the ratio of currents at each electrode can help provide peak purity and identification information. Oxidation and reduction reactions can be carried out simultaneously. Signals from reactions requiring both low and high potentials can be monitored at different sensitivities. A difference signal can be used to remove a common interference. 

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Additional important Information on the size of the separated compounds can be obtained easily by comparison with known compounds having similar characteristics furthermore the characterization of the separated compounds is facilitated by the use of multiple detection systems. 

Using analytical pyrolysis for such samples would be just one component of a systems approach to multimedia analysis, a multifaceted approach to the examination of environmental samples centered upon the use of a purge-and-trap/head-space/pyrolysis/gas chromatography system utilizing multiple detection systems. Although the development of such an analytical scheme was under discussion more than 10 years ago, no analytical method using Py-MS, Py-GC, or Py-GC/MS has yet been promulgated. 

The standard detector for GPC systems is the refractive index (RI) detector, but a feature of developments over the past 10 years is the development of double (RI and viscosity) or triple detector systems (RI, viscosity and light scattering). These multiple detection systems provide measures of true molecular weight by obtaining the actual Mark-Houwink parameters (in the case of the viscosity detector) for the polymer being... 

Limitations in the digitizer s dynamic range can be overcome by using multiple transient recorders operating at diflerent sensitivities, or by adding logarithmic preamplifiers in the detection system. From the preceding discussion it appears, however, that quantitative analysis is not the primary area of application of LIMS. Semiquantitative and qualitative applications of LIMS have been developed and are discussed in the remainder of this article. 

General texts on GC are numerous [118,119] narrow-bore GC was addressed by van Es [120]. Sample introduction techniques and GC inlet systems have been reviewed [25,90] and split/splitless [121] and on-column injection [122] were considered specifically. Stationary phases [123], multiple detection [103], derivatisation [124,125], and quantitative analysis in GC [109] have been described. High-speed GC has recently been reviewed [126]. For a compendium of GC terms and techniques, see Hinshaw [127]. 

Figure 7.21 Dendrimers that are fluorescently labeled as well as biotinylated create enhanced detection reagents for use in (strept)avidin-biotin-based assays. Large complexes containing multiple fluorescent dendrimers can bind to antigens and form a highly sensitive detection system that exceeds the detection capability of fluorescently labeled antibodies.

The presence of biotin labels on an antibody molecule provides multiple sites for the binding of avidin or streptavidin. If the biotin binding protein is in turn labeled with an enzyme, fluoro-phore, etc., then a very sensitive detection system is created. The potential for more than one labeled (strept)avidin to become attached to each antibody through multiple biotinylation sites provides an increase in detectability over antibodies directly labeled with a detectable tag. 

Staggered parallel chromatography is an efficient and capable tool for linking multiple HPLC systems to a serial detection device, the mass spectrometer. The LC2MS version of the LCnMS approach has been in continuous use since 1998 in our laboratory and has supported hundreds of studies. The LCnMS scheme is now available from many commercial venders. However, for users who want to utilize existing equipment and not purchase additional equipment, it is beneficial to configure an ad hoc system from standard HPLC equipment as presented in this chapter. 

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. 

Ideally, a stainer should allow use of multiple antibodies and detection systems during one run. 

This immunostainer does not allow for user-designed protocols, and can use only a single detection system and chromogen per run. Multiple runs per day can be used, however, because of the shortened run time. The elevated temperature that makes this rapid process time available may have deleterious effects on some of the more heat-labile antibodies. We did not have the opportunity to test this in our laboratory. 

Where multiple compressors are involved in the same service or duty, separation should be provided between compressors to reduce mutual exposure. Compressor buildings housing flammable service compressors should be provided with a combustible-gas detection system. The system should alarm at a concentration of 20-25% of the LFL and shutdown the compressor at 40-50% LFL (see Section 8.1.3). The shutdown should include closing all inlet and discharge process lines. For reciprocating compressors in flammable service, explosion vents on the crankcases should be provided. 

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