Traditional detection methods

Before anything else can be said about IEs, some rudimentary chemistry is needed. From a cookbook perspective, all explosives (be they military, commercial, or improvised) require the same chemical building blocks, which consist of a fuel and an oxidizer. Some explosives have the fuel and oxidizer as part of the same molecule, such as trinitrotoluene (TNT), and some explosives are comprised of mixtures of separate fuels and oxidizers, such as ammonium nitrate-fuel oil (ANFO). The oxidizer employed by the vast majority of explosives tends to be the NO2 (nitro) group. It is so predominant as an explosive ingredient that the primary focus of detection methods traditionally has been to look for nitro-derived properties. IEs tend to utilize a more diverse range of oxidizers. Table 3.1 gives a list of the numerous oxidizer possibilities. 

For the above reasons, indoor air filters often yield particle masses that are orders of magnitude below the mass requirements for quantitative ED-XRF analysis - the multi-element detection method traditionally used for air analysis. Researchers are currently seeking alternative multi-element analytical techniques with adequate sensitivity for indoor air samples. Indoor and outdoor air concentration data, from a variety of studies which employed different sampling and analytical approaches, are summarized in Table 11.3. Van Winkle and Scheff (2001) used high-volume samplers equipped with 37-mm quartz fiber filters and an air flow rate of 25 L min to monitor 10 homes in... 

There s a fundamental limitation in traditional gas detection methods. Traditional portable gas detectors provide mobility, but don t communicate. Traditional fixed gas detectors communicate, but aren t portable. The X-zone breaks these limitations 1 combining the mobility of portable systems wHh the communication of forad systems. The result is a level of safety and security unmatched in the industry. This new solution provides flexibility in many applications — from performing confined space entries and area monitoring, to setting up wireless fence lines, to connecting auxiliary safety equipment and transferring alarms to stendtty attendants. With the X-zone, the limits of gas detection are now history. 

Some Chemical Considerations Relevant to the Mouse Bioassay. Net toxicity, determined by mouse bioassay, has served as a traditional measure of toxin quantity and, despite the development of HPLC and other detection methods for the saxi-toxins, continues to be used. In this assay, as in most others, the molar specific potencies of the various saxitoxins differ, thus, net toxicity of a toxin sample with an undefined mixture of the saxitoxins can provide only a rough approximation of the net molar concentration. Still, to the extent that limits can be placed on variation in toxin composition, the mouse assay can in principle provide useful data on trends in net toxin concentration. However, the somewhat protean chemistry of the saxitoxins makes it difficult to define conditions under which the composition of a mixture of toxins will remain constant thus, attaining a reproducible level of mouse bioassay toxicity is difficult. It is therefore useful to review briefly some of the chemical factors that should be considered when employing the mouse bioassay for the saxitoxins or when interpreting results. Similar concepts will apply to other assays. 

Immunoassay Methods. Radioimmunoassay (RIA) allows measurement of biologically active materials which are not detectable by traditional cold chemistry techniques. RIAs can be used to measure molecules that cannot be radiolabeled to detectable levels in vivo. They also are used for molecules unable to fix complement when bound to antibodies, or they can be used to identify cross-reacting antigens that compete and bind with the antibody. 

Since the PSP toxins lack native fluorescence, useful UV absorption or adequate volatility, more traditional analytical procedures such as gas chromatography or spectrometry have proven ineffective in assaying for the toxins. A number of chemical assays for the toxins have been developed though with the fluorometric method of Bates and Rapoport (3 ) proving to be the most useful to date. This assay is based on oxidation of the PSP toxins under alkaline conditions to fluorescent derivatives. The assay is highly sensitive, fairly specific for the PSP toxins and was incorporated into a detection method in the column chromatographic separation of the toxins described by Buckley et al (4 ). 

Despite being relatively new technology, aptamers have a tremendous potential and can be envisioned to rival antibodies and other traditional recognition elements for molecular detection and recognition, due to their inherent affinity, selectivity, and ease of synthesis. In addition, the combination of aptasensors with electrochemical detection methods has the added advantage of further cost reduction and miniaturization of such systems. 

Traditionally, UV detection was by far the most widely used detection method, both in phospholipid class analysis and in molecular species analysis. Even up to now, this detection system re-... 

Whether eluted from columns or from thin-layer plates, the quantitative determination of sugars was traditionally based on colorimetric reactions involving the use of chemical reagents, e.g., anthrone. These detection methods have been largely replaced in modem HPLC by the refractive index detector, although ultraviolet detectors are also employed. Recently we have also seen the introduction of other types of detector (e.g., the mass detector), as will be discussed later. 

EC detection methods have often been considered incompatible with electrophoresis because the combination of high voltages applied for electrophoretic separation and sensitive electrodes is seen as a conflict. However, traditional capillary electrophoresis takes advantage of many of them and with appropriate designs of the detector cell the separation voltage does not interfere with the EC measurement. On the other hand, there are several reports in which this interference is taken as a benefit for generating new detection approaches (see Sections 34.1.3.1 and 34.1.3.2) [52-54],... 

The potential of CE-ICP-MS for use in speciation studies offers the analyst a useful alternative for the separation of compounds of environmental and clinical importance. Detection limits for CE-ICP-MS are often superior to those achieved with traditional detection methods such as refractive index and uv spectroscopy. The use of low-flow nebulizers, such as the direct injection nebulizer and the high-efficiency nebulizer, which can accommodate the low electroosmotic flow of CE, offers significant advantages in terms of improved sensitivity. 

Therefore, heterogeneous catalysts present a greater potential for the application of HT and Combinatorial methods, because they involve diverse compositional phases that are usually formed by interfacial reactions during their synthesis, which in turn produce a variety of structural and textural properties, often too vast to prepare and test by traditional methods. In this respect the HT and Combinatorial methods extend the capabilities of the R D cycle, which comprises the synthesis, the characterization of physicochemical properties and the evaluation of catalytic properties. The primary screening HT method gives the possibility of performing a rapid test of hundreds or thousands of compounds using infrared detection methods [27-29]. Alternatively, a detection method called REMPI (Resonance Enhanced Multi Photon Ionization) has been used, which consists of the in situ ionization of reaction products by UV lasers, followed by the detection of the photoions or electrons by spatially addressable microelectrodes placed in the vicinity of the laser beam [30, 31]. 

Distribution studies with radiolabeled test substances in animals are an important part of the drag development process. Traditional routine methods used for these studies are quantitative tissue distribution studies (QTD) and alternatively whole-body autoradiography (WBA) with detection of the radioactivity in whole-body sections on X-ray film (John R. J. Baker 1989). WBA is a qualitative detection method with a very high local resolution which includes all organs an many small substructures. 

Syndromic surveillance is a work in progress. There is a need for continued development of standardized signal detection methods and signal response protocols (Henning, 2004). Also, whereas reporting of patient information as part of traditional public health surveillance has been deemed exempt from the confidentiality guidelines in the Health Insurance Portability and Accountability Act of 1996 (HIPAA), how those guidelines may be applicable to syndromic surveillance systems remains unclear (Buehler, 2004). 

It is a serious limitation that all these optical techniques can only be used for reactions that are accompanied by significant chromophoric changes, ft is an additional limitation of all these techniques that optical spectra tend to be broad and often show considerable overlap. Therefore reactive species can often not be monitored individually, even in cases where all of them have distinct spectral properties. Optical methods also provide little structural information about the various species in the mixture. The use of traditional stopped-flow is dependent upon the availability of optical signals to monitor change in fluorescence, absorbance or CD that occur upon binding or chemical conversion of substrate to product. In order to overcome these limitations of traditional stopped-flow optical techniques, various detection methods have been developed, such as stopped-flow mass spectrometry (MS), stopped-flow NMR, and stopped-flow EPR. 

The merger of traditional immunocytochemical methods with traditional nucleic acid hybridization techniques has resulted in the development of experimental approaches that serve very effectively for the detection and localization of nucleic acids in biological materials. Furthermore, these in situ methods also may serve for the molecular characterization (e.g., base composition) and quantitation (e.g., copy number) of such nucleic acids. Because of the ubiquitous occurrence of nucleic acids and the sensitivity of the detection methods, the applications are broad and diverse, and often yield information not accessible by other methods. 

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