Radiotracer analysis

Some possible criticisms of the use of radiotracers for monitoring the uptake and release of cocaine are that the tracer chemically reacts with the hair matrix or contains radiolabeled impurities which show preferential binding. Both criticisms are unlikely because (1) the radiotracer never exceeds 1% of the urdabeled drug, and (2) hair exposed to drugs without the radiotracer and analyzed by GC/MS show the parent drug present in amounts indicated by the radiotracer analysis. 

Radiotracer analysis is particularly effective for tracking the fate of additives, because molecular fragmentation can typically be expected to result in an impurity element distribution different from that of the original molecules. For example, in nickel plating in the presence of thiourea, complete incorporation of the molecule should give a carbon/sulfur ratio of 1.0, while experiments indicate a ratio ranging from 0.01 to 0.7 depending on the deposition conditions [130,131,141,142], As with additive incorporation, the decomposition process can be a sensitive function of the co-adsorbates [145, 149, 150]. 

Paris, O. H., and A. Sikora. 1967. Radiotracer analysis of the trophic dynamics of natural isopod populations, pp. 741-771. In Secondary Productivity of Terrestrial Ecosystems, Vol. D (K. Petrusewicz, ed.). Institute of Ecology, Polish Academy of Science, Warsaw. 

Interdiffusion of bilayered thin films also can be measured with XRD. The diffraction pattern initially consists of two peaks from the pure layers and after annealing, the diffracted intensity between these peaks grows because of interdiffusion of the layers. An analysis of this intensity yields the concentration profile, which enables a calculation of diffusion coefficients, and diffusion coefficients cm /s are readily measured. With the use of multilayered specimens, extremely small diffusion coefficients (-10 cm /s) can be measured with XRD. Alternative methods of measuring concentration profiles and diffusion coefficients include depth profiling (which suffers from artifacts), RBS (which can not resolve adjacent elements in the periodic table), and radiotracer methods (which are difficult). For XRD (except for multilayered specimens), there must be a unique relationship between composition and the d-spacings in the initial films and any solid solutions or compounds that form this permits calculation of the compo-... 

Electrochemical as well as nonelectrochemical techniques are used when studying these aspects. Electrochemical techniques are commonly used, too, in chemical analysis, in determining the properties of various substances and for other purposes. The nonelectrochemical techniques include chemical (determining the identity and quantity of reaction products), radiotracer, optical, spechal, and many other physical methods. Sometimes these methods are combined with electrochemical methods for instance, when studying the optical properties of an electrode surface while this is polarized. Nonelectrochemical techniques are described in more detail in Chapter 27. 

Activation analysis, the application of radiotracers and other radiochemical methods in innovative trace analysis are indispensable, first of all in the preparation of standard reference samples. 

For cases of sample storage where losses cannot be excluded a priori, some sort of check is required. This should be done under conditions representative of the actual sampling, sample storage, and sample analysis. As this study indicates, the use of radiotracers is helpful in making such checks. 

Falkner and Edmond [334] determined gold at femtomolar quantities in seawater by flow injection inductively coupled plasma quadrupole mass spectrometry. The technique involves preconcentration by anion exchange of gold as a cyanide complex, [AulCNjj], using 195Au radiotracer (ti/2 = 183 days) to monitor recoveries. Samples are then introduced by flow injection into an inductively coupled plasma quadrupole mass spectrometer for analysis. The method has a detection limit of 10 fM for 4 litres of seawater preconcentrated to 1 ml, and a relative precision of 15% at the 100 fM level. 

Three main features account for the usefulness of radiotracers in analysis. Firstly, a chemical species... 

A recent paper by Lairdinvestigated the efficacy of HPAM flocculation of kaolinite, illite and quartz by carrying out visible absorption experiments. He concluded that HPAM more effectively flocculates kaolinite than quartz or illite. This was also the conclusion of previous work by Allen et al. who studied the adsorption of HPAM onto kaolinite, quartz and feldspar at various HPAM concentrations and solution pH by X-ray photoelectron spectroscopy (XPS). Much of the previous work on polyacrylamide adsorption onto aluminosilicates monitored the adsorbed amount by viscometry, carbon analysis and radiotracer techniques. These methods rely on following adsorption by subtraction from that detected in solution. 

Nuclear chemistry consists of a four-pronged endeavor made up of (a) studies of the chemical and physical properties of the heaviest elements where detection of radioactive decay is an essential part of the work, (b) studies of nuclear properties such as structure, reactions, and radioactive decay by people trained as chemists, (c) studies of macroscopic phenomena (such as geochronology or astrophysics) where nuclear processes are intimately involved, and (d) the application of measurement techniques based upon nuclear phenomena (such as nuclear medicine, activation analysis or radiotracers) to study scientific problems in a variety of fields. The principal activity or mainstream of nuclear chemistry involves those activities listed under part (b). 

The unique advantages of radiotracer experiments include their high sensitivity, their simplicity, and small expense (compared to competing technologies such as mass spectrometry). In a well-designed experiment, the presence of radiotracers does not affect the system under study and any analysis is nondestructive. Interference from other species that may be present is not important (as compared to conventional methods of analysis where interferences may thwart the analysis). 

Today the largest number of applications of radiotracers is in biology and medicine. Because of the large number of applications, it is beyond the scope of this work to review them in any detail. Instead, we shall focus on three specific applications, one that is very old, one that is middle-aged, and one that is adolescent in its scope, if not in its development. We refer to autoradiography, radioimmunoassay, and DNA (deoxyribonucleic acid) analysis, respectively. 

The isotope 40K can be analyzed in natural water samples with the Cherenkov counting technique.2 3 Because of the lack of a suitable radiotracer for K and the similarity between the chemistries of rubidium and potassium, 86Rb can be used as a tracer for K.4 Also, thermal ionization mass spectrometry (TIMS) has been used to determine 40K in environmental samples. The interference of mass 40 can be solved by double spiking with 43Ca/48Ca the procedure for the routine high-precision isotope analysis of the K-Ca system will then be free of Ca fractionations.5... 

Gel electrophoresis (GE) is a common separation technique in protein analysis and it has also been used for the speciation of metals bound to proteins [86]. In most applications, metals have been detected by autoradiography, limiting the studies to those elements for which a relatively stable radionuclide exists [87]. As an example, 75Se radiotracer allowed Se to be detected after two-dimensional GE (2-DE) separation [88]. Owing to the high sensitivity and isotopic capability of ICP-MS, this technique has been proposed as the detection tool of choice for elements in gel. The efbcient transport of the sample from the protein spot on gel to plasma has been achieved by laser ablation (LA) [89, 90] and electrothermal (ET) atomization [62, 91] techniques. The... 

The effect of concentration of cations in the externally applied cocaine solutions on the uptake of cocaine into hair is shown in Figure 8. Cocaine plus radiotracer was added (final concentration, 10 pg/mL) to each of four solutions with different sodium chloride concentrations ranging from 0 to 500 mM. Two sets of samples were studied — each set containing either Caucasian brown hair or Asian black hair. The first set was dried after exposure and prior to decontamination/analysis for cocaine. The second set was carried directly through the decontamination procedure. As seen... 

Thermal neutrons in the reactor are efficient in producing ( , y) neutron capture reactions e.g. Fe (n, y) f< Fe. The products of these reactions will have an excess of neutrons and generally decay by (/ ", y) emission. The major disadvantage is that the radioactive atoms will always be diluted with many -non-radioactive atoms and chemical separation is not possible, (n, y) reactions are however usefully exploited in neutron activation analysis (p. 471). With fast neutrons, proton, deuteron or alpha particle bombardment a change in atomic number accompanies the.reaction and chemical separation of the carrier free radiotracer becomes possible,... 

A method of analysis frequently requires the separation of the analyte from interfering materials present within the sample matrix. Many different procedures are used to effect such separations (chapter 4) and the establish ment of quantitative procedures is a singularly important step in method development. Careful study and control of experimental conditions are needed and a large number of experiments may be required to establish the most suitable. Radiotracers are uniquely suited to such studies. The sensitivity of detection means that only very small amounts of tracer need be added to... 

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