Radiotracer Methods Research Articles

Condensation coefficients and initial stages of growth for noble metals deposited onto chemically different polymer surfaces

The initial stages of growth of noble metals deposited onto untreated as well as Ar + beam-treated polymer surfaces were investigated by means of X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), and radiotracer methods. Condensation coefficients C of the metals on the polymer surfaces were determined by comparison of the XPS signals of the metals with the nominal thicknesses measured by a quartz microbalance during deposition. These measurements were combined with radiotracer measurements, which allow to determine C independently with high accuracy and sensitivity. C was found to depend strongly on the chemical composition of the polymer surface, e.g., at room temperature, C varies between 0.95 for PMDA-ODA polyimide and 0.002 for Teflon AF. By ion beam treatment of the latter, C was raised considerably. During nucleation of the metal on the polymer surface, C increases strongly with metal coverage. C also depends on the deposition rate of the metal and decreases strongly at elevated temperatures.

Radiotracer method for quantifying the amount of platinum and rhodium deposited in automotive catalytic converters

Radiotracer methods have been developed to quantify the amount of platinum and rhodium deposited on automotive catalytic converters as a function of production conditions. In particular, this study determined the effects of selective adsorption and evaporation processes on the aqueous impregnation of converters with platinum group metal salts. The radiotracers used in this study, 191Pt and 105Rh, were produced by thermal neutron activation of Pt and Ru. Chemical processing was performed to remove undesired radioactive products and to ensure that each tracer was in its appropriate chemical state. This radiotracer method has been shown to be capable of measuring the platinum and rhodium loading on an entire substrate with a precision better than ±0.5%. At this precision level, the influence of selective adsorption and evaporation were determined.

Gadolinium determination in tissue samples by inductively coupled plasma mass spectrometry and inductively coupled plasma atomic emission spectrometry in evaluation of the action of magnetic resonance imaging contrast agents.

The quantitative determination of Gd-containing magnetic resonance imaging (MRI) contrast agents in animal tissues is performed by both ICP-AES and ICP-MS. While ICP-AES has been used to determine Gd-containing contrast agents by other workers, no published methodology has been found. An accurate and precise method using nitric acid and microwave digestion for sample preparation is described. Dosed rat tissue, blood and plasma were measured by both ICP-AES and ICP-MS. The ICP-AES method is excellent for screening Gd levels and quantitative determination of concentrations above 400 ng ml-1, but it lacks the sensitivity to measure agent concentrations in low dose MRI studies. This work demonstrates that ICP-MS has the needed sensitivity to replace radiotracer methods currently used for low dose studies, while maintaining the accuracy and precision of results obtained by ICP-AES. Gadolinium detection limits in tissue were 0.04 mumol of Gd per kg of tissue, an order of magnitude lower than studies using radiotracer techniques.

Adrenergic Nervous System in Heart Failure

Recent demonstration that the level of sympathetic nervous drive to the failing heart in patients with severe heart failure is a major determinant of prognosis, and that mortality in heart failure is decreased by β-adrenergic blockade with carvedilol, indicates the clinical relevance of cardiac neuroscience research. Important initial findings were observations that the plasma concentration of the sympathetic neurotransmitter, norepinephrine, is elevated in heart failure, and that overall clinical outcome is related to plasma norepinephrine concentration (although heart failure severity may be a confounder). Sympathetic nerve recording (clinical microneurography) and radiotracer methods measuring regional sympathetic activity in the heart (cardiac norepinephrine “spillover”) have now largely supplanted antecubital venous norepinephrine measurements as research tools, with newer methods providing information on regional sympathetic function that was previously lacking. The cardiac sympathetic nerves are preferentially stimulated in severe heart failure, with norepinephrine release from the failing heart at rest in untreated patients increased up to 50-fold, which is similar to the level of release in healthy hearts during near maximal exercise. There is lesser stimulation of the sympathetic outflows to the kidneys and skeletal muscle. In early mild heart failure, it is only the cardiac sympathetic nerves that are activated. This preferential activation of cardiac sympathetic outflow contributes to arrhythmia development and probably to progression of heart failure and has been linked to mortality in mild and severe heart failure. The central nervous system mechanisms involved in the sympathetic nervous activation present in patients with heart failure remain uncertain. Increased intracardiac diastolic pressure seems to be one peripheral reflex stimulus with increased forebrain norepinephrine turnover being an important central mechanism.

Recovery of spent acid by electrodialysis in the zinc hydrometallurgy industry: Performance study of different cation-exchange membranes

A performance study of four different cation-exchange membranes was conducted on laboratory and pilot scale (172 cm 2/membrane, model CS-0 from Asahi Glass Co.) electrodialysis cells, using Neosepta CMS from Tokuyama Soda Co.; Morgane CRA from Solvay; Selemion CHV from Asahi Glass Co. and Nafion 117 from DuPont, coupled with a Morgane ARA 17-10 anion-exchange membrane. Comparisons were made of the sulphuric acid recovery rate, water transport, metal leakage and energy intake for these membranes. Proton permselectivity and metal leakage, co- and counter-ion transport numbers of the CMS membrane were investigated using Hittorf's method and radiotracer methods. This study shows that electrodialysis is suitable for the treatment of zinc hydrometallurgy effluents. However, R & D work must still be done in order to improve and optimize the technology for its use in future industrial applications. In particular, research efforts must concentrate on the synthesis of affordable and stable cation-exchange membranes showing high selectivity towards protons.

A species-specific bacterial productivity method using immunomagnetic separation and radiotracer experiments

A species-specific bacterial productivity assay, combining radiotracer methods with immunomagnetic bead separation, was developed and tested in the marine environment. The capture method was optimized using cultures of the marine denitrifying strain, Pseudomonas stutzeri (ATCC 14 405). Immunocapture was optimal at a bead to target cell ratio of 10:1 using an indirect antibody technique, in which the target cell is first incubated with specific (primary) polyclonal antiserum and then with the secondary antibody-coated beads. Primary antibody concentration was less important than target cell concentration in determining the efficiency of target cell recovery. Reproducible recovery efficiencies of 75% could be obtained using cultures, but at natural seawater abundance levels, efficiency was much lower, around 20%. Estimates of total heterotrophic bacterial production and P. stutzeri production, based on radiotracer incorporation, were obtained for seawater samples from Monterey Bay, CA. To measure species-specific production, samples were incubated with radiotracers (methyl-[ 3H]-thymidine and [ 14C]-leucine), fixed, and concentrated. After separating P. stutzeri cells from the bacterial assemblage using immunomagnetic separation, target cell fraction radioactivity was measured. P. stutzeri abundance, estimated by immunofluorescence, represented less than 0.1% of the total bacterial abundance, whereas radiotracer incorporation by the target fraction represented 1–3% of the total assemblage tracer incorporation.

Adsorption–Desorption Behavior of Acrylic–Maleic Acid Copolymer at Clay Minerals

The interactions between acrylic–maleic acid (PAA–PMLA) copolymer with clay minerals are investigated in terms of adsorption/desorption behavior. The adsorption isotherms were obtained as a function of clay mineral structures, pH and ionic strength by sensitive polyelectrolyte titration and radiotracer methods. The nature and the location of binding sites for PAA–PMLA copolymer on aluminol sites at the edge surface can be stated. In the case of the adsorption on kaolinite, the pH-dependent interaction in relatively low ionic strength is discussed not only in terms of electrostatic contributions, but evidences for a ligand exchange mechanism are also presented. Increasing the ionic strength also enhances the adsorption by a screening of the charges in the adsorbed layer especially when the charges of the copolymer and the surface are of the same sign. The adsorbed PAA–PMLA copolymer can be displaced by phosphate compounds such as monophosphate and sodium tripolyphosphate (STP). The observed desorption process results from a competition between PAA–PMLA copolymer and phosphate compounds for the same binding sites on the kaolinite surface. Adsorption equilibrium constants can thus be derived from single and mixture adsorption isotherms. Effects due to the heterogeneity of the kaolinite surface and to the conformation of the adsorbed PAA–PMLA copolymer are also discussed. Strongly bound PAA–PMLA copolymer traces support the ligand exchange mechanism at the aluminol sites of the edge surface. Clay minerals may thus act as natural barriers in the soil transport of the polycarboxylates used in phosphate-free detergents.

Potentiometric titration method for determining rates of sulfate reduction in a constructed wetland

The Big Five wetland in Idaho Springs, Colorado, was constructed as a pilot‐scale system to treat metal‐laden acidic mine drainage and to determine optimal design criteria for full‐scale treatment systems. Removal of dissolved metals from the mine drainage occurred primarily through bacterial sulfate reduction and metal‐sulfide precipitation in the substrate of the wetland treatment system. A potentiometric titration method was performed to measure the rate of sulfate reduction in the substrate of the Big Five wetland under optimal conditions for design criteria purposes. Rates of sulfate reduction of 1.6 and 0.94 μmol cnr‐3 day‐1 over incubation time periods of 35 and 17 days, respectively, were determined by a titrimetric method from samples of treatment‐system substrate. The titrimetric method was compared with the more commonly employed 35S radiotracer method. Both the titrimetric and radiotracer methods gave similar rates of sulfate reduction based on results of analyses of split samples of treatment‐system substrate. Advantages of the titrimetric method included avoidance of the necessary certification requirements, safety precautions, and expensive equipment and waste disposal associated with the use of 35S‐labeled sulfate in the most commonly applied radiotracer methods. These advantages allowed easier measurement and correlation of additional system parameters including metals and sulfate. For these reasons, the titrimetric method may be useful for inexpensive, initial treatability studies of acidic mine drainages to provide estimates of sulfate reduction and metal loading rates for various mine drainage and wetland substrate compositions.

Pathophysiology of movement disorders studied using PET.

PET radiotracer methods can measure various biochemical features of brain tissue in the living human brain. Here, local brain energy consumption and striatal dopaminergic function will be discussed in the light of the neurodegenerative processes underlying Parkinson's disease. Particularly, disease progression and its consequences for protective and restorative strategies will be outlined. Also, an example will be given to demonstrate how the effect of neurotrophic factors on the striatal dopaminergic system can be monitored by PET tracer methods.

Corrosion behaviour of duplex stainless steels containing minor ruthenium additions in reducing acid media

The dissolution behaviour, as well as the time, potential and concentration dependence of HSO−4SO2t-4and Cl− accumulations measured by an in situ radiotracer method on surface oxide-layers of duplex stainless steels containing various amounts of ruthenium as additive are presented and discussed. Several independent techniques, such as mass loss tests, potentiodynamic responses, radiotracer and ICP methods, were used to characterize the complex features of the passivation phenomena of steels modified with ruthenium. The experimental results reveal that the interaction of bisulfate/sulfate ions with passive oxide layer is stronger than those of chloride ions on the stainless steels studied. Both the extent and the strong character of bisulfate/sulfate accumulation are more likely related to the redistribution of the main alloying components (Cr, Ni, Mo) as well as the Ru in the surface oxide-film formed on steels passivated spontaneously in dilute HCl and H2SO4. It is found that the ruthenium additions to the base duplex stainless steel significantly increase the corrosion resistance in reducing acid environments. There is evidence of anodic inhibition and this seems to be responsible for the observed increased corrosion resistance of the duplex stainless steels with small ruthenium additions.

Study of the polyaniline film degradation process by radiotracer and electrochemical methods

The electro-oxidative degradation of polyaniline films electrodeposited on the platinum electrode has been studied using radiotracer and potentiodynamic pulse techniques. It was discovered that the surface of the platinum electrode had been covered by polymer chains and is released from them and obtains the ability for adsorption of hydrogen and other particles ( eg, aniline) on released platinum centres. At low potentials such type degradation is not accompanied by mass and doping peak changes. These changes take place at higher potentials of degradation. It was found that aniline monomer units of all layers of film are removed from the polymer at high potentials of degradation.

Applications of nuclear methods in the automotive industry

Over the years nuclear methods have proved to be a valuable asset to industry in general and to the automotive industry in particular. This paper summarizes some of the most important recent contributions of nuclear technology to the development of vehicles having high quality and long-term durability. Radiotracer methods are used to measure engine oil consumption and the wear rates of inaccessible components. Radiographic and tomographic methods are used to image fluids and structures in engines and accessory components. Tracers are used to understand combustion chemistry and quantify fluid flow. Gauging methods are used for inspection and process control. Nuclear analytical methods are used routinely for materials characterization and problem solving. Although nuclear methods are usually considered as the means of last resort, they can often be applied more easily and quickly than conventional methods when those in industrial engineering and R&D are aware of their unique capabilities.

Immunoassays (ELISA) for Rapid, Quantitative Analysis in the Food-Processing Industry

An indirect, competitive-type enzyme-linked immunosorbent assay (ELISA) is shown to have sufficient accuracy, precision, and sensitivity for application to total residue determinations for spectinomycin-related residues in food animal tissues. Assay optimization established the linear dynamic range, sensitivity, and method detection limits. Control tissue extracts were assayed for the presence of either positive or negative interferences. Interferences arising from cross-reactivity with other antibiotics or therapeutic agents likely to be present were evaluated. Recovery and precision from fortified tissue samples as well as measurement of operator bias from the analysis of samples with biologically incurred residues were determined. Equivalency of the ELISA method with standard radiotracer methods of analysis is demonstrated herein. Delivered in the microtiter format and using fully automated sample processing systems, immunoassays, as described, can be used for “real-time” quality control analysis in th...

Regional epinephrine kinetics in human heart failure: evidence for extra-adrenal, nonneural release

A number of neurohumoral processes are activated in heart failure, including an increase in the plasma concentration of epinephrine. Radiotracer methods were applied in 42 patients with severe heart failure and 31 healthy volunteers to ascertain the rate at which epinephrine is released to plasma and to evaluate the contribution of extra-adrenal sources. The increase in arterial plasma epinephrine observed in the heart failure patients was explained principally by a 34% (P < 0.001) reduction in the whole body clearance rate of epinephrine from plasma. Regional venous sampling from the heart, lungs, and hepatomesenteric beds was performed in a subgroup of the study population, revealing a significant increase in the release rate of epinephrine to plasma from these organs in heart failure which accounted for 26% of the whole body plasma epinephrine appearance rate. To establish whether the cardiac epinephrine release was of neuronal origin, a physical (cycling) or mental (difficult mental arithmetic) stressor was applied as a sympathoexcitatory stimulus, given that a proportional release of norepinephrine and epinephrine could be expected if sympathetic nerves were the source. These interventions caused significant increases in the regional spillover of norepinephrine to plasma but not that of epinephrine. These findings suggest that nonadrenal tissues contribute significantly to the whole body epinephrine release rate in heart failure and that this may arise from a site other than sympathetic neurons.

Evaluation of a fluorescent microparticle technique for measuring filtering rates of Daphnia

The paper demonstrates the applicability of fluorescent microparticles (FMP) for the determination of cladoceran feeding rates. For this purpose we examined the relation between filtering rate, ingestion rate, gut passage time and body length of Daphnia pulex at different food concentrations in laboratory experiments, and diurnal changes of filtering rates of Daphnia longispina in in situ experiments, using FMPs as tracer particles. Good agreement of our results with published data based on cell counts and radiotracer methods proves the suitability of the FMP-method. Potentials and limitations of the method are discussed.

Benthic-pelagic coupling in the Greenland-Norwegian Sea and its effect on the geological record

The sedimentation pattern of organic material in the Greenland-Norwegian Sea is reflected in the surface sediments, although less than 0.5% of the organic matter is buried in the sediment. Maximum fluxes and benthic responses are observed during June and/or August/September, following the pattern of export production in the pelagial zone. The annual remineralization rate on the Vøring Plateau is 3.0 g C m−2 a −1 Freshly settled phytodetritus, as detected by chlorophyll measurements, is rapidly mixed into the sediment and decomposed. It stimulates the activity of benthic organisms, especially foraminifera. The mixing coefficient for this material is D b=0.2 cm2 d−1, which is two to three orders of magnitude higher than that estimated from radiotracer methods. The effect on the geological record, however, is likely to be small. Chlorophyll-containing particles are at first very evenly distributed on the seafloor. After partial decomposition and resuspension, a secondary redistribution of particles occurs which can result in the formation of a high accumulation area, with an up to 80-fold increase in the sedimentation rate by lateral advection. This is mainly due to physical processes, because biodeposition mediated by benthic animals increases sedimentation by only a factor of two or three.

Toxicity of selected pesticides to lake phytoplankton measured using photosynthetic inhibition compared to maximal uptake rates of phosphate and ammonium

AbstractThe toxicity of 16 pesticides to the energy‐producing process of photosynthesis was determined from inhibition or depression of the assimilation rate of [14C]bicarbonate by natural plankton samples collected from Jack's Lake, a mesotrophic lake on the edge of the Canadian Shield 200 km northeast of Toronto, Ontario. Measurements were made at increasing concentrations of pesticide while samples were exposed to optimal light. At the same time, in the same 300‐ml bottle, measurements of maximal uptake rates for phosphate and ammonium were made using radiotracer and stable isotope methods. In this way the more commonly used screening technique of photosynthetic inhibition could be compared to the energy‐demanding processes of phosphate and ammonium uptake. Phosphate assimilation was inhibited at much higher herbicide concentrations than carbon fixation, whereas ammonium assimilation was inhibited at intermediate concentrations. Herbicides that specifically inhibit photosynthesis were most toxic to carbon uptake, while those herbicides affecting other cellular metabolic processes had a greater influence on phosphate and ammonium assimilation. No relationship was found among pesticide toxicity and molecular weight, solubility, or log Kow.

New approaches to evaluate sympathoadrenal system activity in experiments on Earth and in space

In previous studies the activity of the sympathoadrenal system (SAS) in cosmonauts during space flights was evaluated by measuring plasma catecholamines (CA) levels and urinary CA and their metabolites concentrations. Plasma CA levels are accepted indicators of SAS activity, however, they are determined by the plasma clearances as well as the rates of CA release (spillover-SO) into the bloodstream. Nowadays methods are available which evaluate not only plasma levels of CA but also their release, spillover, uptake, reuptake, degradation and also CA synthesis in vivo measured by plasma levels of dihydroxyphenylalanine (DOPA). Plasma concentrations of DOPA, the CA noradrenaline (NE), adrenaline (ADR), and dopamine (DA), the deaminated catechol metabolites dihydroxyphenylglycol (DHPG) and dihydroxyphenylacetic acid (DOPAC), and the O-methylated metabolites methoxyhydroxyphenylglycol (MHPG) and homovanillic acid (HVA) were measured during immobilization stress (IMO) in conscious rats. Radiotracer methods were used to measure NE SO. IMO markedly increased arterial NE levels but NE SO was less elevated bacause the NE clearance was slightly reduced in IMO rats. Simultaneous measurements of plasma CA and their metabolites provide another means to obtain information about SAS function. For instance, dissociation between changes of plasma DHPG and NE levels can indicate changes in neuronal reuptake of NE. We found marked parallel increases in plasma NE and DHPG levels during acute IMO; however after repeated IMO, plasma NE levels were increased but DHPG responses were less pronounced suggesting a reduced NE reuptake. DOPA, the CA precursor, circulates in plasma at a concentration higher than NE. During stress, increased sympathoneural outflow stimulates DOPA synthesis and release into the circulation supporting the view that changes in plasma DOPA levels during stress reflect in vivo changes in the rate of CA synthesis. We propose to measure the new plasma indicators of SAS activity in cosmonauts and/or in animals before, during and after space flights.

Aluminum gettering of cobalt in silicon

We investigated the gettering effect of an evaporated aluminum layer on single crystalline and cast multicrystalline silicon doped with radioactive cobalt-57 by means of radiotracer methods and Mössbauer spectroscopy. We present evidence that aluminum gettering works at high temperatures and transfers the cobalt atoms from the Si bulk to the liquid Al-Si phase. Presumably Al gettering can be explained as a segregation induced process caused by a higher solubility of the metallic impurity in the liquid Al-Si phase compared with that in solid silicon.

The impact of a coccolithophore bloom on oceanic carbon uptake in the northeast Atlantic during summer 1991

Measurements of the carbonate system in the surface waters of the northeast Atlantic during summer 1991, following the main growth phase of a bloom of the coccolithophore Emiliania huxleyi are presented. We examine the perturbation of the carbonate system and assess the effect of calcification on the air-sea gradient of dissolved carbon dioxide in the surface ocean. An estimate of 1:1 organic to inorganic carbon uptake is calculated using the measurements of the surface carbonate parameters which is consistent with other estimates for E. huxleyi populations using radio-tracer methods. Using the changing ratio of dissolved carbon dioxide to nitrate concentration we demonstrate a relative increase in dissolved carbon dioxide due to calcification with evidence of this increase supported by estimates of the buffer factor and C:N assimilation ratios. Within the E. huxleyi bloom the effect of calcification on alkalinity appears to have reduced the air-sea gradient by ∼ 15 μatms (corrected to a constant temperature) using measurements from a 440 km section along the 20°W meridian. This reduction could prove to be significant in terms of the overall drawdown of carbon during the spring-summer season in this area.