Radiometric detection

Radiometric detection technology offers high sensitivity and specificity for many appUcations in scientific research. The radioactive emission of the labeled compound is easily detected and does not suffer from interference from endogenous radioactivity in the sample. Because of this unique property, labeled compounds can be used as tracers to study the localization, movement, or transformation of molecules in complex experimental systems. 

Radiometric detection technology, 21 271 Radiometric ore sorting, 16 626 Radiometric techniques, for plutonium analysis, 19 699-700 Radiometry, 23 142-143 Radionuclide removal... 

Often the products of nuclear reactions have very short half-lives. This is especially true for the heaviest elements obtained by bombardment of heavy targets with heavy ions. To identify and characterize such short-lived nuclides, fast separations are required solvent extraction techniques are well suited to provide the required fast separations. For example, the SISAK method [68] has been successfully used in conjunction with in-line gas jet separators at heavy ion accelerators to identify short half-life actinide isotopes produced by collision of heavy atoms. The Sisak method involves use of centrifugal contactors, with phase residence times as low as tenths of a second, in conjunction with in-line radiometric detection equipment. 

The distribution and elimination of SARA from tissue of juvenille channel catfish was evaluated as the loss of radioactivity of SARA Cl 4 in liver, kidney, skin, and skinless fillet. An HPLC with fluorescence detection, in-line radiometric detection, and gradient elution was applied (203). The pharmacokinetics of ENRO in the milk of lactating cows was studied by HPLC, and it was found that a marked proportion of ENRO was metabolized to CIPRO (204). 

Metabolite identification can be conducted on several levels, ranging from straightforward analyses for targeted species to more complex analyses utilizing radiometric detection, MS, and possibly other detectors. A process flow for profiling and characterization of metabolites by LC-MS is presented in Fig. 1.34. There is an increasing emphasis on quality metabolite data from relatively early in discovery (Fernandez-Metzler et al., 1999), and some of the fundamental approaches that can be used have been summarized by Anari and Baillie (2005). 

In this radiometric detection approach, the detection limit could be lowered by using a stopped-flow procedure that captured 89% of the eluted "Tc within a 2.5-mL flow-through counting cell. Continuous-flow and stopped-flow detector traces are... 

Sample preparation is required to cope with the sample matrix, the interferences, and the speciation of "Tc. The separation processes for isolating "Tc prior to radiometric detection require that the "Tc be in the pertechnetate ("TCO4) state. However, in waste samples with high organic content, much of the "Tc may be present in reduced valence states. Therefore, to determine the total "Tc content, all the "Tc must be oxidized to the pertechnetate state prior to ion-exchange or extraction-chromatographic separation. 

Egorov, O. B., O Hara, M. J., Ruzicka, J., and Grate, J. W., Sequential injection system with stopped flow radiometric detection for automated analysis of 99Tc in nuclear waste, Ana/. Chem., 70, 977-984, 1998. 

In the example of a-human atrial natriuretic peptide (ANP), found at increased plasma levels in patients with heart failure, Numata et al. [70] demonstrated how IPCR sensitivity accelerated conventional assay procedures. For individual treatment of the cardiac patients, a prompt detection of atrial distension by the presence of the ANP marker would be desirable. Common ANP tests, however, take 2-3 days for the quantification of plasma by radiometric or ELISA techniques. With sandwich IPCR, the assay time could be shortened to 5 hours. A good correlation between IPCR and radiometric detection was maintained, combined with an additional improvement of the detection limit to 2 ng/L ANP. The average level of ANP in plasma for 25 patients with heart failure was found to be 117 100 ng/L, significantly higher than the typical level of 20 14 ng/L for healthy subjects. 

The TRAP (telomeric repeat amplification protocol) assay is a widely used method for detection of telomerase activity. This technique measures the telomerase activity present in cell extracts. Briefly, cellular extract containing telomerase activity is incubated with a telomeric substrate (a short strand of DNA onto which the telomerase wiU. attach the telomeric repeats) followed by polymerase chain reaction (PCR) amplification of the elongated telomere. Detection of the PCR product is by a number of methods, including gel electrophoresis, radiometric detection, ELISA, and real-time PCR detection. ... 

Measurement of labelling yield and subsequent radiochemical purity requires a suitable analytical technique, and the method of choice for radio-labelled peptides is reversed phase HPLC with on-line UV and radiometric detection. It is important to use as stringent a separation method as possible with isocratic or slow mobile phase composition gradients over the peptide peak. Ideally, more than one mobile phase system should be used (e.g. a phosphate buffer-methanol system in addition to the standard water-acetonitrile system), since these may show the presence of new impurities. It is important to recognize that HPLC analyses only measure those components that elute from the column. Insoluble, highly lipophilic or positively charged species may bind to the solid phase. It is very important to verify the absence of these species by a complimentary technique such as thin layer chromatography (TLC) and to ensure that the two techniques produce similar results. 

Yu, C. et al., A rapid method for quantitatively estimating metabolites in human plasma in the absence of synthetic standards using a combination of liquid chromatography/ mass spectrometry and radiometric detection, Rapid Commun. Mass Spectrom., 21(4), 497, 2007. 

Preliminary studies for airborne systems were reported by Meeks et al. (87), who studied microwave radiometric detection of oil slicks. A couple of years later, Fantasia and Ingrao (88) and Ingrao et al. (89) described the development of an experimental airborne remote sensing system for oil spills, based on laser-stimulated oil fluorescence. At the Tenth International Symposium on Remote Sensing, in 1975, several techniques were reported, including a passive infrared (90), radar observation of spills (91), passive luminescence with a Fraunhofer line discriminator (FLD) (92), and active luminescence (93) and fluorescence (94). 

Application of radiometric detection in high-performance column liquid chromatography 158... 

There is a large variety of analytical problems that require the separation of radioactive species by column liquid chromatography. This need arises, for instance, in activation analyses, the separation of fission products or the separation of radioactively labelled compounds. Examples of special importance come from the biosciences, where labelled molecules are used in research on metabolism. Whenever a sample contains radioactive species, it is possible to follow their elution from a separation column specifically by radiometric detection. This review outlines briefly the principles of radiometric detection and radiometric detectors, concentrating on problems that arise from the combination of separations by high-performance column liquid chromatography with radiometric detection. 

The Origin of these problems is the inherently statistical character of the radioactive decay which influences the precision of radiometric detection systems. 

APPLICATION OF RADIOMETRIC DETECTION IN HIGH-PERFORMANCE COLUMN LIQUID... 

The following sections give an Introduction to the literature on radiometric detection in HPLC, emphasizing papers on the design and performance of on-line radiometric detectors. The number of papers in this field is still rather small. 

As high-performance column liquid chromatography has rarely been applied in inorganic radiochemistry, only a few papers can be cited to illustrate the combination of HPLC with radiometric detection in this field. The pioneering work of Horwitz et a1. shows the scope of high-performance column liquid-liquid chromatography with off-line radiometric detection in inorganic radiochemical and isotope separation. 

Advantages and Limitations of Radiometric Titrations. Radiometric detection of the equivalence point is a general method that does not depend on the chemical reaction employed. This contrasts with other methods of detection, which depend on specific chemical or physical transitions at the equivalence point. Amperometric titrations are applicable only to electrochemically active systems conductometric titrations apply only to ionic solutions, and so on. In principle, any titration system in which a phase separation can be effected is amenable to radiometric detection, provided there exist suitable radioactive labels. The major limitation of the method is the requirement for phase separation. In precipitation titrations, the phase separation is automatic and the method is well suited to this class of titrations. For other classes of titrations, special phase-separation methods, such as solvent extraction, need to be applied. At the present time, the method suffers from a lack of phase-separation techniques suitable for continuous monitoring of the titration curves. 

Kaniansky, D., Rajec, R, Svec, A., Havasi, R, and Macasek, F., Online radiometric detection in capillary isotachophoresis. 1. Preliminary experiments, J. Chromatogr., 258, 238, 1983. 

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