Radiochemical Detection

We have been unable to demonstrate any reaction between cyanatryn -oxide and DNA in vitro or between cyanatryn and liver DNA in vivo(2). Three hours after oral doses of []cyanatryn giving about 2 (1.98 and 2.41) yg of cyanatryn equivalents per g of liver, the perfused livers were removed, pooled and used to prepare protein, RNA and DNA fractions(14). Values expressed as yg of cyanatryn per g of pooled liver were total, 2.19 protein, 0.29 RNA fractions, 0.002 DNA fraction, not detectable. Radiochemical in the combusted sample of DNA was not detectable, i.e. less than 1 dpm/mg. This value is equivalent to 1 mol of triazine to 10 mol of guanine. Cyanatryn and its -oxide apparently possess low reactivity towards nitrogen nucleophiles. 

All immunoassay procedures are based on the original discovery by Berson and Yalow that low concentrations of antibodies to the antigen hormone insulin could be detected radiochemically by their ability to bind radiolabeled ( I) insulin. The determination of unknown concentrations of antigen, then, is based on the fact that radiolabeled antigen and unlabeled antigen (from the sample or a standard) compete physiochemically for the binding sites on the antibodies (radioimmunoassay, RIA). This is illustrated in Figure 24.5. 

Radiochemical tracers, compounds labeled with radioisotopes (qv), have become one of the most powerful tools for detection and analysis in research, and to a limited extent in clinical diagnosis (see Medical IMAGING TECHNOLOGY). A molecule or chemical is labeled using a radioisotope either by substituting a radioactive atom for a corresponding stable atom in the compound, such as substituting for H, for or for P, and for for... 

The NAA measurements on the paper samples were made at the Breazeale Nuclear Reactor Facility at the Pennsylvania State University with a TRIGA Mark III reactor at a flux of about 1013 n/cm2-sec. Samples were irradiated from 2 to 20 min and counted for 2000 sec, after a 90 min decay time for Ba and a 60 hr decay for Sb, Analyses were performed instrumentally, without radiochemical separation, using a 35cm3 coaxial Ge-Li detector and a 4096-channel pulse height analyzer. With these procedures, detection limits for Ba and Sb were 0.02ug and 0.001 ug, respectively. These sensitivities are comparable to those obtained by GA s radiochemical separation procedure, and are made possible by the use of the higher neutron output from the more powerful reactor and in combination with the higher resolution solid state detector... 

Watmough, N.J.. Turnbull, D.M., Sherratt. H.S.A. Bartlett. K. (1989). Measurement of the acyl-CoA intermediates of p-oxidation by hplc with on-line radiochemical and photodiode-array detection. Application to the study of [U- C]hexadecanoate by intact rat liver mitochondria. Biochem. J. 262,261-269. 

In cases where the induced radionuclides of trace elements are masked by matrix activity, radiochemical separation provides interference-free detection limits close to... 

The detection of the migrating sample boundary in CE can be accomplished by UV, fluorescent, electrochemical, radiochemical, conductivity, and mass spectrometry (MS) means. The use of high-sensitivity detection systems is always a key issue in CE applications. The sensitivity of HPCE detectors may be at least 2 to 3 orders of magnitude better than that of HPLC detectors. Since the detection cell volume is very small, the concentration sensitivity... 

For the analysis of americium in water, there is a broad array of sample preparation and detection methodologies that are available (see Table 7-2). Many of the common and standardized analytical methodologies typically include the minimization of sample volume, purification through co-precipitation, anion exchange column chromatography, and solvent extraction techniques followed by radiochemical detection of americium in the purified sample. Gross alpha analysis or liquid scintillation are common... 

There are methods available to quantify the total mass of americium in environmental samples. Mass spectrometric methods provide total mass measurements of americium isotopes (Dacheux and Aupiais 1997, 1998 Halverson 1984 Harvey et al. 1993) however, these detection methods have not gained the same popularity as is found for the radiochemical detection methods. This may relate to the higher purchase price of a MS system, the increased knowledge required to operate the equipment, and the selection by EPA of a-spectrometry for use in its standard analytical methods. Fluorimetric methods, which are commonly used to determine the total mass of uranium and curium in environmental samples, have limited utility to quantify americium, due to the low quantum yield of fluorescence for americium (Thouvenout et al. 1993). 

Photoactivation analysis has also been used to determine fluoride in seawater [73]. In this method a sample and simulated seawater standards containing known amounts of fluoride are freeze-dried, and then irradiated simultaneously and identically, for 20 min, with high-energy photons. The half-life of 18F (110 min) allows sufficient time for radiochemical separation from the seawater matrix before counting. The specific activities of sample and standards being the same, the amount of fluoride in the unknown may be calculated. The limit of detection is 7 ng fluoride, and the precision is sufficient to permit detection of variations in the fluoride content of oceans. The method can be adapted for the simultaneous determination of fluorine, bromine, and iodine. 

Hiraide et al. [68] used continuous flow coprecipitation-floatation for the radiochemical separation of cobalt from seawater. The 60cobalt activity was measured by liquid scintillation counting with greater than 90% yield and a detection limit of 5 fCi/1 seawater. 

At the same time, in this laboratory, we detected the dimethyl acetals of D-xylose and D-glucose by chromatographic resolutions of the products of methanolsis of labelled free sugcirs, and we have, likewise, concluded that they are not primary products but are formed either concurrently with the furanosides or, more probably, from them 8). Fig. 3 illustrates the variations of the main components of the reaction of D-xylose as determined by radiochemical counting of the chromato-graphically resolved components (the pyranosides were vmresolved under the conditions used), and in Fig. 4 the concentration of the acetal is... 

Neutrino detectors are placed at great depths, at the bottom of mines and tunnels, in order to reduce interference induced by cosmic rays (Fig. 5.3). Two methods of detection have been used to date. The first is radiochemical. It involves the production by transmutation of a radioactive isotope that is easily detectable even in minute quantities. More precisely, the idea is that a certain element is transformed into another by a neutrino impact, should it occur. Inside the target nucleus, the elementary reaction is... 

DNB in biological samples (Miller et al. 1991). The method showed good specificity and comparable recovery of 1,3-DNB from blood samples when compared with HPLC/UV and HPLC/radiochemical detection. No information was located that specifically discussed the detection of 1,3,5-TNB and metabolites in blood and urine by any method. 

Another consideration when choosing a detector is whether it is important to preserve the separated analytes, either for use or for further analysis. Some methods, such as evaporative laser scattering detection and mass spectrometry, destroy the sample during the measurement. Other methods, such as fluorescence or radiochemical detection, may require chemical labeling of the analytes ... 

Unlike the majority of other HPLC detectors, radiochemical detection is based on time, and detection of low abundance peaks can be improved by adjusting the flow rate. Slower flow rates allow for more counting time and therefore increased accuracy and sensitivity. Even so, radiochemical detection often suffers from reduced sensitivity due to high background. 

FIGURE 7.11 Schematic for radiochemical detection of analytes labeled with beta-particle emitters. Radio-labeled analytes in the column effluent are mixed with scintillation cocktail to produce light, which is detected and measured by the paired photomultiplier tubes and relayed to a data acquisition system. 

FIGURE 7.12 Schematic for radiochemical detection of gamma-emitting analytes. The analytes within each peak are measured by a photomultiplier tube placed in close proximity to or incorporated into the aluminum shell of the detector. 

Wehmeyer KR, Kasting GB, Powell JH, Kuhlenbeck DL, Underwood RA, Bowman LA. Application of liquid-chromatography with online radiochemical detection to metabolism studies on a novel class of analgesics. Journal of Pharmaceutical and Biomedical Analysis 8, 177-183, 1990. 

Rajagopalan P, Gao ZL, Chu CK, Schinazi RF, McClure HM, Boudinot FD. High-performance liquid-chromatographic determination of (-)-beta-D-2,6-diaminopurine dioxolane and its metabolite, dioxo-lane guanosine, using ultraviolet and online radiochemical detection. Journal of Chromatography. B, Biomedical Applications 672, 119-124, 1995. 

Kaivosaari S, Salonen JS, Mortensen J, Taskinen J. High-performance liquid chromatographic method combining radiochemical and ultraviolet detection for determination of low activities of uridine 5 -diphosphate-glucuronosyltransferase. A a/yft ca/ Biochemistry 292, 178-187, 2001. 

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