Platinum group elements study in automobile catalysts and exhaust gas samples.

Platinum-Group Elements (PGEs, i.e. platinum; Pt, palladium; Pd and rhodium; Rh) are extensively employed in the production of automotive catalytic converters to catalyze and control harmful emissions from exhaust fumes. But catalytic converters wear out over time and the emission of PGEs along with the exhaust fumes are nowadays known to be the main reason of the presence of PGEs in urban environments. PGEs contents were studied on three gasoline 3-way catalytic convertors with low, medium and high kilometers. PGEs emission factors via exhaust gases from Euro 3, 4, 5 and 6 gasoline and diesel vehicles, were monitored using catalytic converters. Results show variable content for PGEs for the three converters, in the ranges of 6-511, 0.5-2507 and 0.1-312 mg kg-1 for Pt, Pd and Rh respectively. PGEs contents in different catalyst supports show the replacement of Pt by Pd in more recent converters. Analysis of the exhaust gas shows that catalytic converters expel up to 36.5 ±â€¯3.8 ng km-1 of Pt, 8.9 ±â€¯1.1 ng km-1 of Pd and 14.1 ±â€¯1.5 ng km-1 of Rh. Higher emissions of PGEs have been observed by gasoline Euro 3 vehicle, possibly due to the older technology of motorization and of the catalytic converter in this vehicle. Euro 3 and 4 diesel vehicles seem to emit more PGEs during urban cycles. Emission of PGEs has been also observed during the cold start of the majority of vehicles which seems to be the result of incomplete combustion during the rise of temperature in the engine. Higher PGEs emissions were also observed during motorway cycles in newer (Euro 4 and 5) petrol and diesel vehicles, conceivably due to the greater combustion as the engine speeds up during this cycle.

APPLICATION OF THE EUROPEAN PROTOCOL IN THE EVALUATION OF DIGITAL MAMMOGRAPHY UNITS WITH TUNGSTEN TARGET TUBES.

The performance of the first direct digital mammography unit in Gozo General Hospital, the Hologic Selenia Dimensions 2D, was assessed by applying the European Protocol for quality control in mammography screening. This system employs a Tungsten anode in association with a Rhodium or Silver filter, depending on the compressed breast thickness. The objective of this article was to apply the European Protocol in the evaluation of this system in terms of dose, image quality and detector performance and determine whether this system is suitable for use in the national breast-screening program.

Intrinsic catalytic activity of rhodium nanoparticles with respect to reactive oxygen species scavenging: implication for diminishing cytotoxicity.

Noble metal nanoparticles (NPs) and their hybrids have demonstrated a strong potential to mimic the catalytic activity of natural enzymes and diminish oxidative stress. There is a large space to explore the intrinsic catalytic activity of Rh NPs with respect to reactive oxygen species (ROS) scavenging. We found that Rh NPs can quench H2O2, •OH, O2•-, 1O2 and inhibit lipid peroxidation under physiological conditions. In vitro cell experiments proved that Rh NPs have great biocompatibility and protect cells from oxidative damage caused by H2O2. This study can provide important insights that could inform future biological applications.

Platinum, palladium, and rhodium in airborne particulate matter.

Measurable quantities of platinum, palladium, and rhodium, even in remote areas of the planet, evidence the global nature of pollution with these metals, mostly from catalytic converters of modern vehicles (other sources are jewellery production, chemical industry, and anticancer drugs). The amount of the platinum group metals (PGMs) emitted from automobile catalysts varies with the type, age, and condition of the engine and the catalyst, as well as the style of driving. Current literature suggests that the concentrations of these metals have increased considerably over the last twenty years, palladium concentrations in particular, as it has been proved more effective catalyst than platinum. However, whether and to what extent the emitted PGMs are toxic for people is still a controversy. The potential health risk from exposure to these elements is most likely for those living in urban environments with busy roads or along major highways. Because of the importance of PGMs and their trace levels in particulate matter, sensitive methods are required for reliable determination. This review discusses particular steps of analytical procedures for PGM quantification in airborne particulate matter and addresses the common preparation, detection, and determination methods.

Determination of Ultra-trace Rhodium in Water Samples by Graphite Furnace Atomic Absorption Spectrometry after Cloud Point Extraction Using 2-(5-Iodo-2-Pyridylazo)-5-Dimethylaminoaniline as a Chelating Agent.

A highly sensitive method based on cloud point extraction (CPE) separation/preconcentration and graphite furnace atomic absorption spectrometry (GFAAS) detection has been developed for the determination of ultra-trace amounts of rhodium in water samples. A new reagent, 2-(5-iodo-2-pyridylazo)-5-dimethylaminoaniline (5-I-PADMA), was used as the chelating agent and the nonionic surfactant TritonX-114 was chosen as extractant. In a HAc-NaAc buffer solution at pH 5.5, Rh(III) reacts with 5-I-PADMA to form a stable chelate by heating in a boiling water bath for 10 min. Subsequently, the chelate is extracted into the surfactant phase and separated from bulk water. The factors affecting CPE were investigated. Under the optimized conditions, the calibration graph was linear in the range of 0.1-6.0 ng/mL, the detection limit was 0.023 ng/mL for rhodium and relative standard deviation was 3.67% (c = 1.0 ng/mL, n = 11)．The method has been applied to the determination of trace rhodium in water samples with satisfactory results.

Glandular radiation dose in tomosynthesis of the breast using tungsten targets.

With the advent of new detector technology, digital tomosynthesis imaging of the breast has, in the past few years, become a technique intensely investigated as a replacement for planar mammography. As with all other x-ray-based imaging methods, radiation dose is of utmost concern in the development of this new imaging technology. For virtually all development and optimization studies, knowledge of the radiation dose involved in an imaging protocol is necessary. A previous study characterized the normalized glandular dose in tomosynthesis imaging and its variation with various breast and imaging system parameters. This characterization was performed with x-ray spectra generated by molybdenum and rhodium targets. In the recent past, many preliminary patient studies of tomosynthesis imaging have been reported in which the x-ray spectra were generated with x-ray tubes with tungsten targets. The differences in x-ray distribution among spectra from these target materials make the computation of new normalized glandular dose values for tungsten target spectra necessary. In this study we used previously obtained monochromatic normalized glandular dose results to obtain spectral results for twelve different tungsten target x-ray spectra. For each imaging condition, two separate values were computed: the normalized glandular dose for the zero degree projection angle (DgN0), and the ratio of the glandular dose for non-zero projection angles to the glandular dose for the zero degree projection (the relative glandular dose, RGD(alpha)). It was found that DgN0 is higher for tungsten target x-ray spectra when compared with DgN0 values for molybdenum and rhodium target spectra of both equivalent tube voltage and first half value layer. Therefore, the DgN0 for the twelve tungsten target x-ray spectra and different breast compositions and compressed breast thicknesses simulated are reported. The RGD(alpha) values for the tungsten spectra vary with the parameters studied in a similar manner to that found for the molybdenum and rhodium target spectra. The surface fit equations and the fit coefficients for RGD(alpha) included in the previous study were also found to be appropriate for the tungsten spectra.

Enhanced sensitivity of lithium dithionates doped with rhodium and nickel for EPR dosimetry.

Electron paramagnetic resonance (EPR) studies of X-irradiated lithium dithionate, Li(2)S(2)O(6) x 2H(2)O, doped with Ni and Rh have shown that these impurities enhance the yield of radicals formed by X-irradiation at room temperature. The signal in the doped samples, measured peak-to-peak of the single EPR derivative line attributed to the SO(3)(-) anion was about 3-4 times that of the pure lithium dithionate and more than 10 times stronger than the alanine signal. These impurities also shortened the spin-lattice relaxation time, T(1), which gives the possibility to measure the doped samples at a higher microwave power. This implies that sensitivity could be further enhanced in the already sensitive EPR dosimeter material lithium dithionate.

Significance of platinum group metals emitted from automobile exhaust gas converters for the biosphere.

INTENTION, GOAL, SCOPE, BACKGROUND: Following the introduction of automobile catalytic converters the platinum group metals (PGM) platinum (Pt), palladium (Pd) and rhodium (Rh) gain on increasing interest in environmental research as these metals are emitted with exhaust fumes into the environment. Consequently, elevated PGM levels were found in different environmental matrices such as road dusts, soils along heavily frequented roads, sediments of urban rivers etc. Accordingly, the effects of increasing PGM emissions on the biosphere are controversially discussed. OBJECTIVE: This paper summarizes the present knowledge on the biological availability of PGM to plants and animals. As biological availability is one of the most decisive factors determining the toxicological potential of xenobiotics, this information is very important to evaluate the possible threat of the noble metals to ecosystems. RESULTS AND DISCUSSION: The availability of soluble as well as particle bound PGM to terrestrial plants was demonstrated in several studies. Experimental investigations revealed uptake of Pt, Pd and Rh also by aquatic plants. Additionally, the biological availability of the noble metals for animals has been verified in experimental studies using soluble metal salts, catalytic converter model substances, sediments of urban rivers, road dust or tunnel dust as metal sources. These studies refer mainly to aquatic animals. Beside of free living organisms, in particular worms parasitizing fish demonstrated a high potential to accumulate PGM. This could be of great interest in respect of biomonitoring purposes. Generally, for plants as well as for animals Pd turns out to be the best available metal among the PGM. Compared to other heavy metals, the biological availability of PGM from road dust to zebra mussels (Dreissena polymorpha) ranged between that of Cd and Pb. CONCLUSION: Especially chronic effects of PGM on the biosphere can not be excluded due to (1) their cumulative increase in the environment, (2) their unexpected high biological availability and bioaccumulation and (3) their unknown toxicological and ecotoxicological potential. However, it appears that acute effects on ecosystems due to anthropogenic PGM emission are not likely. RECOMMENDATION AND OUTLOOK: Research on environmental PGM contamination of the biosphere, especially the fauna, and on long-term toxicity of low PGM concentrations is highly appreciated. These studies require very sensitive analytical techniques to determine PGM even in low sample amounts. Research has to be done in particular on reliable determination of (ultra) trace levels of Pd and Rh as the lack of data on these two metals is mainly due to analytical problems.

[Determination of trace platinum, palladium, gold and rhodium in geological samples by ICP-AES after preconcentration by diphenlthiourea immobilized on aluminum oxide].

A method for the determination of Au, Pt, Pd and Rh by ICP-AES after preconcentration on a column containing diphenylthiourea immobilized on aluminum oxide was developed. The optimum acidity of solution, amount of adsorbent, elution solution, flow rate and volume of the samples were obtained for the elements studied. The effect of interfering ions on the recovery of the analytes was also investigated. Under the optimum measuring conditions, the recoveries were found to be between 95%-105%. The detection limits of Au, Pd, Pt and Rh was 0.0085, 0.022, 0.015 and 0.022 microgram.g-1, respectively, and the relative standard deviation was lower than 5%. This procedure was applied to the determination of Au, Pd, Pt and Rh in geological samples.

Measurements and nuclear model calculations on proton-induced reactions on 103Rh up to 40 MeV: evaluation of the excitation function of the 103Rh(p,n)103Pd reaction relevant to the production of the therapeutic radionuclide 103Pd.

Excitation functions were measured by the stacked-foil technique for the reactions 103Rh(p,n)103Pd, 103Rh(p,3n)101Pd and 103Rh(p,4n)100Pd from their respective thresholds up to 39.6 MeV. The radioactivity of the activation products was determined by high-resolution X-ray and gamma-ray spectrometry. Statistical model calculations taking into account the precompound effects were performed for all reactions, and good agreement was found with our data. A critical evaluation of the existing and present data for the 103Rh(p,n)103Pd reaction was carried out. Recommended cross sections and integral yields for this reaction of key importance in the production of the widely used therapeutic radionuclide 103Pd are given.