The determination of natural uranium in human tissues by recovery corrected kinetic phosphorescence analysis

Two typical methods used for the determination of uranium in human autopsy tissues are kinetic phosphorescence analysis (KPA) and alpha-spectrometry, both of which have significant limitations and advantages. KPA is limited because of the amount of sample used (1–10 ml for sample digestion followed by one ml KPA aliquots), no isotopic information is provided, phosphorescence degradation by salts in solution, and even more importantly, it does not provide chemical recovery information. For samples with sub ng uranium concentrations per g of inorganic material, preconcentration is necessary, which may require chemical recovery (other than simple evaporation). While alpha-spectrometry has very good radiometric detection limits for ²³⁸U, the very long half-life of ²³⁸U (4.468·10⁹ y) restricts its mass detection limit (27 ng). KPA, on the other hand, has a detection limit three orders of magnitude lower (0.02 ng) for natural uranium. A recovery corrected method for the determination of natural uranium in human tissues was developed combining preconcentration of human tissues dissolved in 6M HCl by anion exchange with alpha-spectrometry and kinetic phosphorescence analysis, utilizing ²³²U as a tracer. Solution aliquots containing up to 6 g of bone ash were pre-concentrated for KPA measurement thereby allowing the use of up to 25% of the original sample solution weight for analysis by KPA. The radiochemical yield of ²³²U was determined by alpha-spectrometry and the uranium content was determined by KPA. The mean radiochemical yields obtained for human tissue samples range from 65% to 106% with a mean of 85%±8%.     

Comparison of direct kinetic phosphorescence analysis and recovery corrected kinetic phosphorescence analysis for the determination of natural uranium in human tissues

Summary In the analysis of biological samples with sub ng/g uranium concentrations, pre-concentration has been shown to improve the detection limit for the determination of uranium. Recovery corrected kinetic phosphorescence analysis (KPA) combines pre-concentration and separation of uranium by anion-exchange from human tissues dissolved in 6M HCl, with the radiochemical yield determined by alpha-spectrometry, using ²³²U as a tracer. Total uranium is determined by KPA after correction for chemical recovery. Twenty-one randomly selected dissolved tissue samples from the United States Transuranium and Uranium Registries (USTUR) Case 0242 were chosen for comparative analyses. The set of samples included dissolved bone and soft tissues. Uranium concentrations for seven of the samples had not been previously reported. Direct KPA could not be used to determine uranium concentrations of five unreported tissues. Three of these tissues had uranium concentrations at or below the KPA L_Q value of 0.028 ng/ml and two tissues had known matrix interferences. All seven of the unreported tissues were successfully analyzed by recovery corrected KPA; concentrations ranged from 9 to 1380 ng per tissue, including those that could not be analyzed by direct KPA due to matrix problems. Recovery corrected KPA gives results similar to direct KPA where matrix interferences and low detection limits are not encountered. A comparison of the direct method of KPA versus recovery corrected KPA shows marked improvement for the determination of uranium in samples that heretofore either uranium was not detected or the sample had to be drastically diluted to minimize matrix effects in order to measure uranium.     

Determination of uranium concentration in urine of workers in an Iraqi phosphate mine and fertilizer plants

Precise determination of uranium concentration in human urine is quite important in assessment of occupational and public exposure to uranium. In the present work, a pulsed dye nitrogen laser-induced kinetic phosphorescence analysis (KPA) was used to determine uranium in urine of Iraqi phosphate mine and fertilizer plant workers and in the population living near the mining region. A total of 92 urine samples were collected from workers of the Akashat phosphate mine, the Al-Qaim fertilizer complex, and the Akashat residential region. Uranium concentration in urine of all samples ranged between 0.49 to 5.26 μg L^?1 with a total average of 1.47 ± 0.01 μg L^?1. For comparison, all samples were also analyzed using a completely different technique; the nuclear fission track analysis using CR-39 SSNTD. Both techniques were capable of such measurements, although not with an equal degree of uncertainty. KPA technique is found to be more suitable for analysis of urine samples having high concentrations of uranium.     

Phosphoric acid as uranium complexant in kinetic phosphorimetry

Phosphorimetry is an analytical technique for the determination of elemental uranium concentration in aqueous environmental or biological samples. Uranium phosphorescence from aqueous samples at room temperature is practically undetectable without the addition of a uranium complexant, i.e., a solution whose molecules bind to the uranyl ions present in the sample under measurement and protect them from non-luminescent de-excitation. Procurement of commercially available and proprietary in nature complexant solutions can prove cost in-effective. On the other hand, phosphoric acid is known for its phosphorescence protecting capabilities. This study investigates the optimisation of phosphoric acid use as uranium complexant, and assesses it in terms of accuracy, precision and longevity, with rather encouraging results.     

Comparison of different alcohols in a caged lumophore for measuring supersaturated dissolved oxygen

Intense phosphorescence is observed when an alcohol is introduced to an aqueous solution containing 1-bromonaphthalene and a cyclodextrin complex. The enhancement of the phosphorescence intensity of 1-bromonaphalene is related closely with the alcohol’s effectiveness in shielding the photo-excited lumophore from dissolved oxygen. The phosphorescence intensity decreases and the phosphorescence decay rate increases as the dissolved oxygen concentration increases. In this paper, we measure the phosphorescence intensity and decay rate of the complex using different alcohols and explain their respective advantages. By relating the concentration of oxygen to the intensity and the lifetime of the phosphorescence, the dissolved oxygen concentration can be measured. The sensitivities and measurement ranges with the complexes containing different alcohols are compared. Currently, this technique can measure dissolved oxygen concentrations from 0 to 40.2 mM (31,400% saturation). The range of the measurement is 40 times larger than previous studies.     

Determination of uranium isotopes in environmental samples

The determination of isotopes of uranium by alpha spectrometry in different environmental components (sediments, soil, water, plants and phosphogypsum) is presented and discussed in this paper. The alpha spectrometry is a very convenient and good technique for activity concentration of natural uranium isotopes (²³⁴U, ²³⁵U, ²³⁸U) in environmental samples and provides the most accurate determination of isotopic activity ratios between ²³⁴U and ²³⁸U. The analysis were provided information about possible sources of high concentrations of uranium in the examined sites determined by anthropogenic sources. The calculation of values ²³⁴U/²³⁸U in all analyzed samples was applied to identifying natural or anthropogenic uranium origin. Activity concentration of uranium isotopes in analyzed environmental samples shows that measurement of uranium levels is of great importance for environmental and safety assessment especially in contaminated areas (phosphogypsum waste heap).     

A rapid method for determining nanogram quantities of uranium in urine using the kinetic phosphorescence analyzer

A procedure for determining total uranium in urine using a pulsed-laser Kinetic Phosphorescence Analyzer (KPA) is described. The chemical procedure is simple and rapid, and the operation of the KPA is straightforward. An inter-laboratory comparison (measuring total uranium by using fused pellet fluorometry, alpha spectrometry, and the KPA) demonstrates accuracy. The detection limit for this method, of 0.06 ng/mL, is readily achieved. The relative standard deviation (RSD) of the measurements at the 1.0 ng/mL level is 5%. Interference studies, which include selected elements found in urine, are discussed. Potential interferences in other matrices such as soil, milk, and water are also examined.     

ON THE ROOM TEMPERATURE PHOSPHORESCENCE OF WOOL KERATIN

Abstract—A study has been made of the room-temperature phosphorescence behaviour of wool keratin and its major constituent proteins. The 290 nm induced phosphorescence of wool, previously thought to decay by second-order kinetics, is shown to consist of two separate components which decay exponentially with lifetimes of 0.18 × 0.03 and 1.45 × 0.25 s. Selective oxidation of the tryptophyl residues eliminates the long-lived phosphorescence, but has no effect on the short-lived component. The latter is variable in its intensity, and depends upon the history of the fibre. The origins of the different emissions are discussed, and the possible involvement of the phosphorescent species in the photochemical reactions leading to discoloration of the fibre are considered.     

The phosphorescence of benzene obtained byab initio and semi-empirical calculations

Summary Radiative decay and phosphorescence of triplet stare benzene is doubly -orbital and spin- forbidden and is only activated through vibronic coupling among the manifold of triplet states. For this reason the determination of lifetime and transition moments for the decay of triplet benzene has posed a considerable challenge to both theory and experiment. In the present work we have addressed the triplet benzene problem at several levels of theory; by truncated perturbation theory and semiempirical, CNDO/S-CI, calculations; by complete sum-over-state calculations as implemented in recentab initio multiconfiguration quadratic response (MCQR) theory; and by direct MCQR calculations of vibronic phosphorescence. The vibronic coupling is in the two former cases treated by the Herzberg-Teller (H-T) perturbation theory, involving four main mechanisms for the phosphorescent decay of triplet benzene. The results and interpretations given by these approaches as well as their merits and limitations are presented and discussed in some detail. Our calculations indicate that the phosphorescent decay of the³ B _1u state takes place predominantly through vibronic coupling along thee _2g mode. We obtain a phosphorescence that is almost completely out-of-plane polarized, which is in line with more recent measurements by the microwave-induced delayed phosphorescence technique, and could reproduce quite well the intensity ratios for different vibronic bands obtained in that experiment. The final triplet state lifetime is the result of a delicate sum of contributions from several vibronic degenerate and non-degenerate modes. The direct vibronic phosphorescence calculations predict a long lifetime, about one minute — 68 seconds for the best wavefunction — and seem to focus on a doubling of the assumed, albeit not established, best experimental value for the radiative lifetime of triplet benzene; 30 seconds.Dedicated to Inga Fischer-Hjalmars on her 75th birthday     

Temperature dependence of tryptophan phosphorescence in proteins

The phosphorescence yield and decay kinetics of tryptophan (Trp) in apoazurin from Pseudomonas aeruginosa, subtilisin Carlsberg, Staphylococcal nuclease and liver alcohol dehydrogenase were determined as a function of temperature from 150 K (glassy matrix) to 300 K (fluid solution). The constancy of the lifetime-normalized phosphorescence yield with apoazurin and with Trp-314 in alcohol dehydrogenase establishes that the intersystem crossing quantum yield is practically unaffected across the temperature range. Consequently, any decrease in phosphorescence intensity not accounted for by lifetime-shortening is a signal either of the selective quenching of specific Trp residues in the same macromolecule or that the protein sample is heterogeneous in its emission properties. From an analysis of the thermal profile it is concluded that subtilisin Carlsberg and S. nuclease, as opposed to apoazurin, are not phosphorescent at ambient temperature, their residual emission probably arising from protein impurities. Criteria for distinguishing conformer emission from a contribution by protein impurities are discussed.     

Phosphorescent sensor for robust quantification of copper(II) ion

A phosphorescent sensor based on a multichromophoric iridium(III) complex was synthesized and characterized. The construct exhibits concomitant changes in its phosphorescence intensity ratio and phosphorescence lifetime in response to copper(II) ion. The sensor, which is reversible and selective, is able to quantify copper(II) ions in aqueous media, and it detects intracellular copper ratiometrically.     

The phosphorescence nanocomposite thin film with rich oxygen vacancy: Towards sensitive oxygen sensor

Organic room temperature phosphorescent (ORTP) materials provide an exciting research direction for phosphorescent oxygen (O₂) sensors due to their high sensitivity and rapid response to O₂. However, most pure ORTP materials are tightly-packed aromatic compound crystals in a face-to-face manner, which largely prohibits effective O₂ diffusion for sensing. Thus, how to solve this contradiction still faces huge challenges. Here, the use of organic phosphorescent indicator carbon dots (CDs), inorganic matrix layered double hydroxides (LDHs) and polymers (PVA) successfully prepared an ultra-long RTP composite film whose phosphorescence decay intensity is linearly related to O₂ concentration. More importantly, the use of the abundant O₂ defects (Vo) on the surface of the inorganic matrix LDHs to adsorb O₂, which further accelerates the phosphorescence quenching of the thin film and improves the O₂ response. This strategy will provide the possibility to develop high-sensitivity phosphorescent O₂ sensors from a new perspective.     

An improved method for the determination of uranium isotopes in environmental samples by alpha-spectrometry

In order to improve the selectivity of the uranium isotopes determination in environmental samples, further studies have been carried out, including (1) interference of ²¹⁰Po with uranium isotope determination, (2) distribution coefficients of polonium between 5% TOPO in toluene and aqueous hydrochloric and nitric acids, (3) decontamination factor of uranium from polonium of the recommended procedure, and (4) leaching effect comparison of two different leaching procedures in a lichen sample. Based on the new findings, a more accurate extraction chromatographic/ a-spectroscopy method has been developed. For the method's validation, four kinds of reference materials supplied by the IAEA have been tested. It is observed that nearly all the ²³⁸U, ²³⁴U and ²³⁵U concentrations obtained are in good agreement with the recommended or information values, showing that the method can give reliable results. A comparison with existing uranium determination methods has also been made. It is concluded that due to involving preconcentration and chemical separation, the extraction chromatographic/a-spectroscopy method is a more selective, very sensitive and accurate, and low cost method. This revised version was published online in July 2006 with corrections to the Cover Date.     

Development of radiochemical analysis of uranium isotopes in highly contaminated soil samples

An accurate and reliable analytical technique of uranium isotopes in highly contaminated soil samples was developed and applied to the IAEA reference samples. The conventional TBP method of uranium isotopes is insufficient to completely purify uranium from actinides such as plutonium and americium isotopes in highly contaminated soil samples. For overcoming the demerits of the conventional TBP extraction method, sample materials were decomposed with HNO₃ and HF, and uranium isotopes were purified by TBP extraction and anion exchange columns and extraction chromatography. Among the purifying methods of uranium, with a TRU Spec resin column after TBP solvent extraction, uranium was completely separated from the radionuclides in a highly contaminated samples. With the modified TBP extraction method, it was found that the concentrations of uranium isotopes were consistent with the reference values reported by the IAEA.     

Dual-emissive Iridium(III) Complexes as Phosphorescent Probes with Orthogonal Responses to Analyte Binding and Oxygen Quenching

Phosphorescent probes often show sensitive response toward analytes at a specific wavelength. However, oxygen quenching usually occurs at the same wavelength and thus hinders the accurate detection of analytes. In this study, we have developed dual-emissive iridium(III) complexes that exhibit phosphorescence responses to copper(II) ions at a wavelength distinct from that where oxygen quenching occurs. The complexes displayed colorimetric phosphorescence response in aqueous solutions under different copper(II) and oxygen conditions. In cellular imaging, variation in oxygen concentration over a large range from 5 % to 80 % can modulate the intensity and lifetime of green phosphorescence without affecting the response of red phosphorescence toward intracellular copper(II) ions.     

Study of the heavy atom-induced room temperature phosphorescence properties of melatonin and its analytical application

Liquid phase room temperature phosphorescence (RTP) properties of melatonin were studied using heavy atom induced-room temperature phosphorescence (HAI-RTP) technique. 1.2 M potassium iodide was used as a heavy atom reagent together with 0.002 M sodium sulphite as deoxygenating agent to produce the RTP signal. The maximum phosphorescence emission and excitation wavelengths of melatonin were 290 and 457 nm, respectively. The effect of potassium iodide concentration on the RTP lifetime of melatonin was also investigated and based on the results, the rate constants for phosphorescence decay (k(p)) and radiationless deactivation through reaction with heavy atom (k(h)) were determined. Based on the obtained results, a simple and sensitive room temperature phosphorimetric method was developed for the determination of melatonin. The method allowed the determination of 10.0-200 ng ml(-1) melatonin in aqueous solution with the limits of detection and quantification of 3.6 and 12 ng ml(-1), respectively. The proposed method was satisfactorily applied to the determination of melatonin in commercial pharmaceutical formulations.     

Determination of the individual spin-lattice relaxation rates between the spin levels of phosphorescent triplet-state molecules

It is shown how one can determine the individual spir-lattice relaxation rates of a phosphorescent triplet-stale molecule from analysis of the recovery curve in the phosphorescence intensity upon a microwave sweep through one of the zero-field transitions.     

Combined application of alpha-track and fission-track techniques for detection of plutonium particles in environmental samples prior to isotopic measurement using thermo-ionization mass spectrometry

The fission track technique is a sensitive detection method for particles which contain radio-nuclides like ²³⁵U or ²³⁹Pu. However, when the sample is a mixture of plutonium and uranium, discrimination between uranium particles and plutonium particles is difficult using this technique. In this study, we developed a method for detecting plutonium particles in a sample mixture of plutonium and uranium particles using alpha track and fission track techniques. The specific radioactivity (Bq/g) for alpha decay of plutonium is several orders of magnitude higher than that of uranium, indicating that the formation of the alpha track due to alpha decay of uranium can be disregarded under suitable conditions. While alpha tracks in addition to fission tracks were detected in a plutonium particle, only fission tracks were detected in a uranium particle, thereby making the alpha tracks an indicator for detecting particles containing plutonium. In addition, it was confirmed that there is a linear relationship between the numbers of alpha tracks produced by plutonium particles made of plutonium certified standard material and the ion intensities of the various plutonium isotopes measured by thermo-ionization mass spectrometry. Using this correlation, the accuracy in isotope ratios, signal intensity and measurement errors is presumable from the number of alpha tracks prior to the isotope ratio measurements by thermal ionization mass spectrometry. It is expected that this method will become an effective tool for plutonium particle analysis. The particles used in this study had sizes between 0.3 and 2.0 μm.     

Sensitized phosphorescence of benzil-doped ladder-type methyl-poly(para-phenylene)

The delayed luminescence and phosphorescence of ladder-type methyl-poly(para-phenylene) (MeLPPP) doped with benzil at a concentration of 20% by weight has been measured. The introduction of benzil leads to a dramatic reduction of the polymer singlet emission. At the same time, a new band with maximum at 611 nm appears, corresponding to the phosphorescence of MeLPPP. The phosphorescence decay on the short time scale is close to an exponential law with a time decay of 15 ms. This indicates that benzil can efficiently sensitize the phosphorescence of the polymer. In addition, a broad and featureless emission is observed in the delayed luminescence spectra of benzil-doped MeLPPP, which is attributed to an exciplex formed between the polymer host and the dopant. We further observe that the delayed fluorescence is enhanced by the addition of benzil. It is concluded that the delayed fluorescence of benzil-doped MeLPPP is mainly due to the annihilation of triplet excitons on the polymer. Finally, efficient triplet-triplet energy transfer from the benzil-doped polymer to the red-emitting phosphorescent dye Pt(II)octaethylporphyrin is established.     

Effect of humic acid,pH and ionic strength on the sorption of Eu(III) on red earth and its solid component

A highly sensitive separation procedure has been developed to investigate uranium and thorium activities and their isotopic ratios in environmental water samples in Tokushima, Japan. Uranium and thorium isotopes in environmental water samples were simultaneously isolated from interfering elements with extraction chromatography using an Eichrom UTEVA™ resin column. After the chemical separation, activities of U and Th isotopes coprecipitated with samarium fluoride (SmF₃) were measured by α-spectrometry. It has been confirmed that uranium isotopes are isolated successfully from thorium decay chains by analyzing a test aqueous solution as a simulation of an environmental water sample. The separation procedure has been first applicable to the determination of U and Th activities and their isotopic ratios in a drinking well water named “Kurashimizu” in Tokushima City, Japan. The specific activities of ²³⁸U and ²³²Th in “Kurashimizu” were deduced to be within the upper limits of <0.31 and <0.19 mBq/l, respectively.