Radioisotopes detection limit

IEC continues to have numerous applications to the detection and quantification of various inorganic ions.1 1 This is particularly true in water analysis.5-14 Inorganic ions in a variety of other sample types, such as food and beverages,1518 rocks,19-23 biological fluids, (blood, urine, etc.),24-31 pharmaceutical substances,32 33 concentrated acids,34 alcohols,35 and cleanroom air36 have also been analyzed by IEC. IEC has also been employed in isotopic separation of ions,37 including the production of radioisotopes for therapeutic purposes.3839 Typical IEC sample matrices are complex, and may contain substances that interfere with measurement of the ion(s) of interest. The low detection limits required for many IEC separations demand simple extraction procedures and small volumes to avoid over-dilution. Careful choice and manipulation of the eluent(s) may be needed to achieve the desired specificity, especially when multiple ions are to be determined in a single sample. 

Other detection modes employed in capillary electromigration techniques include chemiluminescence [69-71], Raman spectroscopy [72,73], refractive index [74,75], photothermal absorbance [76,77], and radioisotope detection [78]. Some of these detection modes have found limited use due to their high specificity, which restricts the area of application and the analytes that can be detected, such as radioisotope and Raman-based detection that are specific for radionuclides and polarizable molecules, respectively. On the other hand, the limited use of more universal detection modes, such as refractive index, is either due to the complexity of coupling them to capillary electromigration techniques or to the possibility of detecting the analytes of interest with comparable sensitivity by one of the less problematic detection modes described above. 

In the analysis of total uranium, colorimetric detection methods are also possible, depending on the detection limits required. This is a case of measuring a radioactive element, as opposed to a specific radioisotope of an element. In this case, separation methods are used to preconcentrate the uranium to increase the analysis sensitivity and decrease the detection limits.18 21... 

Radioisotope detection of P, 14C, and Tc was reported by Kaniansky et al. (7,8) for isotachophoresis. In their work, isotachophoretic separations were performed using fluorinated ethylene-propylene copolymer capillary tubing (300 pm internal diameter) and either a Geiger-Mueller tube or a plastic scintillator/photomultiplier tube combination to detect emitted fi particles. One of their reported detection schemes involved passing the radiolabeled sample components directly through a plastic scintillator. Detector efficiency for 14C-labeled molecules was reported to be 13-15%, and a minimum detection limit of 0.44 nCi was reported for a 212 nL cell volume. 

On-line radioisotope detection has been demonstrated to be a practical alternative to UV absorbance detection when gel-filled capillaries are used for CE separations. Significant Improvement in detection limits is realized with radioisotope detection. The greatest improvement is realized for small molecules and is roughly one to two orders of magnitude (for runs in which the residence time is not enhanced). 

The refractory inclusions provide the best samples since they incorporated all three of these radioisotopes, as well as °Be. It has already been mentioned that " Ca and A1 are highly correlated in CAIs and hibonite grains (Figure 2). At face value, this would imply the same source for both these refractory elements. A problem with "Ca, however, is that its abundance is only marginally above detection limits and it decays very quickly, so that there is essentially no chance to test for concordant decay between the " Ca and A1 systems. This is not the case for A1 and Be, which exist in much higher abundances and which have half-lives that differ by only a factor of two. 

Enzymes are currently the most widely used and investigated labels for immunoassays, because a single enzyme label can provide multiple copies of detectable species. This catalytic amplification results in immunoassay detection limits that rival those of radioimmunoassay without the storage and disposal problems associated with radioisotopes. Enzyme immunoassays label either ligands or antibodies with enzyme, and enzyme activity in bound or free fractions is measured. Heterogeneous immunoassays employing enzymatic labels have been named enzyme-linked immunosorbent assays (ELISAs). ELISA methods usually employ antibody immobilized onto the wells of polystyrene microtiter plates, and may be... 

The limits of sensitivity for detection are also dependent upon the nature of the radioisotope in the substrate as well as the analytical method employed to separate and detect substrate, intermediate, and products. In our experience, radiolabels are particularly effective with a detection limit of 4-5% of the total radiolabeled species comprising intermediate for less energetic isotopes such as or H, and less than 1 % detection limit for more energetic isotopes. If the reaction is reversible and depending on the kinetic pathway, there is also the option of looking for the intermediate in the reverse direction by starting with the product. Enzyme reactions that contain an irreversible step(s) are much more challenging since a fewer number of the options are available. 

Theoretically the combination of several radioisotope sources each one suitable for excitation of elements with different Z should lead to considerable improvement of the possibilities of the method. The determination of 11 elements has been reported by Belakova et al. (1995) in medicinal plants using Pu, Am/Ag and I as excitation sources. The detection limit of 0.5 mg/kg has not been enough in the case of Hg and Se, and no analysis of standard reference materials is performed. 

Various techniques can be used for quantitative analysis of chemical composition, including (i) optical atomic spectroscopy (atomic absorption, atomic emission, and atomic fluorescence), (ii) X-ray fluorescence spectroscopy, (iii) mass spectrometry, (iv) electrochemistry, and (v) nuclear and radioisotope analysis [41]. Among these, optical atomic spectroscopy, involving atomic absorption (AA) or atomic emission (AE), has been the most widely used for chemical analysis of ceramic powders. It can be used to determine the contents of both major and minor elements, as well as trace elements, because of its high precision and low detection limits. 

Zone refining is a powerful tool for separation and concentration. Following preconcentration, conventional analytical techniques are used to identify and quantify the impurity. This has enabled certain observed abnormalities in properties to be correlated with the presence of impurities in ultratrace amounts that had earlier remained undetected. In another version, the distribution coefficient, k, of a metallic solute is determined by adding its radioisotope under the conditions of the zoning experiment. If the concentration of the nonradioactive form of the solute in the starting material is measurable by an available analytical technique but subsequently falls below the detection limit after refining, its final concentration can still be calculated from the value of k and the zone refining curves. 

Various CL-based analyses of vitamin B12 are listed in Tables 27.2 and 27.3 for pharmaceutical and food samples. Compared with conventional analytical techniques, such as microbiological assay, high-performance liquid chromatography (HPLC), atomic absorption spectroscopy (AAS), radioisotope isotope assay, and fluorimetric detection, the current proposed CL method was more sensitive with a detection limit of 5 pg/mL. 

ICP-MS is a good option for determining various radioisotopes with limits of detection comparable to radiometric methods in a shorter time, especially sensitive for the determination of isotopes with very long lives. However, low-resolution quadrupole ICP-MS is susceptible to isobaric interferences, e.g. " Pu/ " Am, Tc/ Ru, U/ Pu, molecular interferences, e.g. Pu/ UH, and spectral interferences, e.g. also high concentration of dissolved solids should be avoided in order... 

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