Fimit of Detection

With a focus on trace forensic detection of explosives, especially for use in counterterrorism and to counter narcotics investigations, Fetterolf et al. [75] evaluated the use of ion mobility-mass spectrometry for explosives determinations. In this, explosives residues were collected on a membrane filter by a special attachment on a household vacuum cleaner. Although subsequent thermal desorption and analysis required only 5 s, fimits of detection for most common explosives were as low as 200 pg. The persistence of explosives on hands and transfer to other surfaces were also examined as were post-blast residues of NG on fragments of improvised explosive devices constructed with double-based smokeless powder. Finally, postblast residue from C-4, Semtex, and other explosives was found by IMS analyses on items of forensic and evidentiary value. These few out of many examples demonstrate that mobihty spectrometers are well suited tools for laboratory and on-site investigations, before and after the use of explosives. 

Biological processes in nature can also create the opposite effect—formation of more stable, less degradable compounds. Phenols are biomethylated in the environment to their corresponding anisoles which are more stable and lipophilic. This means that phenol pollution studies must also take into account formation and bioaccumulation of anisoles. Biomethylation of phenols to more bioaccumulating anisoles has not only environmental, but also economic consequences, as chloroanisoles are extremely bad-tasting compounds. For example, in sensory panel studies of water solutions, the concentration fimit of detectable odor was lowered 3 to 10 orders of magnitude during anisole formation in... 

An electrostatic ion chromatographic method was developed for the direct determination of iodide, bromide and nitrate in seawater (Hu et ai, 1999). An octadecylsifica column modified with a zwitterionic surfactant 3- NJV-dimethylmyristylammonio)propane-suifonate was used as the stationary phase, and an electrolytic solution was used as the eluent. The matrix species (such as chloride and sulfate) were retained weakly, and showed iitde or no interference. The method was applied to the determination of iodide, bromide, and nitrate in artificial seawater, giving detection fimits of 0.8 p,g 1 for iodide, 0.75 p.g 1 for bromide, and 0.52 p,g 1 for nitrate, and relative standard deviations of <1.2%. The real seawater samples were also analyzed successfully. Later, another electrostatic ion chromatographic method was developed for the determination of iodide in seawater by the same research group (Hu et ai, 2002). A reversed-phase ODS column was... 

Note that search is a serial sequential process, terminating upon successful detection of a discrete indication (such as a surface scratch) caU a target in visual search. Because of its sequentieil nature, it is a resource-hmited rather than data-fimited process (Wickens 1991). As such, the probability of detection increases with time spent searching in a manner dependent upon the search plan. 

A study comparing detection limits for GC/MS analysis of 2,4-DNT, TNT, RDX and PETN, using El, Cl and NICI, showed that NICI gave the lowest detection fimits, which were between 0.18 and 1.11 ng [8]. 

In this section, results of three different experimental methods that have been apphed to Pd(2-thpy)2 are reported. Information from optically detected magnetic resonance (ODMR spectroscopy), microwave-recovery measurements, and phosphorescence microwave double resonance (PMDR spectroscopy) is presented. These methods complement each other to a large extent. The discussion presented here can be fimited to the basic impfications of the methods, since a comprehensive review by Max Glasbeek concerning these aspects is found in Volume 213 of this series [90] and a detailed report by Glasbeek, Yersin et al. [61] concerning Pd(2-thpy)2 has only recently been published. 

In situations where a lower detection fimit is required and highly specific antisera are not available, cortisol is first extracted from serum before measurement. The extraction is performed in a manner similar to that for urine specimen extractions (see discussion later in this chapter). An important advantage of the direct assays is their superior precision compared with assays involving extraction. In part this may reflect the variability inherent in manual extraction techniques. In general, however, with the high specificity of the antibodies available today and with the use of very sensitive nonisotopic techniques, such as chemiluminescence and fluorescence, the quantitative measurement of cortisol in blood and urine is now relatively straightforward. 

The pursuit of chemical agents that can more effectively treat cancer has led to many decades of research by a multitude of chemists, biochemists, microbiologists, biologists, and research physicians. Thousands of chemicals have been synthesized and tested in tissue cultures and animal models. Only a modest number have proved to be useful in treating humans, but they have become the mainstay of the chemotherapeutic attack on cancer. In combination with early detection, surgery, radiation, and newly developing immunotherapies and targeted therapies, the judicious use of chemotherapy can kill tumors and fimit their recurrence. 

Radon has a tiny natural abxmdance as the product of uranium and thorium decay it has a backgroxmd concentration of 6 X 10 " parts per million by volume in air. Because radon is a short-fived a-emitter, the synthesis of compounds that contain radon has been fimited to just fluorides and oxides. Radon saw considerable therapeutic use between 1920 and 1950 in the irradiation of tumors, but its modern usages stem from its being an easily detected radioactive gas. It is used to trace gas flow and air movement, and... 

Michalke and Schramel (1999) reported a method of CE coupled to ICP-MS for the speciation analysis of iodine. A buffer comprising phosphate (pH 2.3), NaOH, sodium dodecyl sulfate (SDS) and borate (pH 8.3) for stacking was employed for the separation of iodide, iodate, T4 and T3. The separated four iodine species were subsequently detected during a pressure-driven detection step (basehne-separated) at 19.5, 29.1, 36.6 and 42.2 s. The detection fimits were determined at 0.08 p,g I/l (iodide), 0.3 p.g I/l (iodate), 3.5 p.g I/l (T4) and 2.5 p,g I/l (T3). This method has been appfied for iodine speciation in human serum and urine. The serum from a healthy person contained iodide (13p.g I/l), T4 (6lp,g I/l) and T3 (7.5p.g I/l), whereas the serum from a thyroid-operated person lacked T3. 

An X-ray fluorescence method has been developed for in vivo determination of iodine in thyroid (Aubert et al., 1981 Jonckheer and Deconinck, 1982). This method is based on the irradiation of iodine in the thyroid by o(-rays provided by a -source, such as Am. The excited iodine atoms emit a characteristic X-ray fluorescence radiation, which is proportional to the amount of iodine present in the gland. The reported detection fimit reaches 0.01 mg/ml thyroid, this value is much lower than the iodine concentration in thyroid. The reported radiation dose equivalent is only 60mSv per measurement. This method has been successfully used for the clinical determination of in thyroid (Milakovic et al., 2006 Reiners et al., 1996, 2006 Briancon et al., 1992). An indirect method was also reported to determine of thyroid iodine in vivo (Imanishi et al., 1991), which is based on the relationship of CT attenuation values with iodine concentration in the thyroid. It was reported that the CT value correlated finearly with iodine concentration in thyroid nodules when iodine concentration was higher than 0.02 mg/g. 

In this area, techniques to gain information on the reaction mechanism by detecting intermediates have to be developed to gain insights into the bottleneck that fimits the efficiency of the process and to provide hints of how to control the... 

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