Glassy carbon tubes for electrothermal atomic absorption spectrometry

Summary The use of glassy carbon as a tube material in electrothermal atomic absorption spectrometry requires modifications to the power supply if temperatures and heating rates comparable to those for graphite tubes are to be obtained. Glassy carbon tubes frequently have a longer lifetime than pyrolytic graphite coated tubes made of polycrystalline electrographite. Peak height sensitivity for glassy carbon is better by a factor of two for some volatile elements, but up to a factor of five inferior for less volatile elements than that for pyrolytic graphite coated tubes. Peak area sensitivity is generally inferior by about a factor of two. Sample volume is limited to 5–10 l because of the smooth surface.From the signal shape it can be deduced that adsorption of analyte atoms at the tube wall plays an important role in glassy carbon, and is responsible at least in part for the lower sensitivity. Non-spectral interferences can be less pronounced in glassy carbon tubes for those interferents which interact with graphite tube surfaces. Glassy carbon is, however, no alternative to pyrolytic graphite coated tubes.

---

Glasartiger Kohlenstoff als Rohrmaterial für elektrothermische Atomabsorptionsspektrometrie

     

Seasonal variation, chemical behavior and kinetics of uranium in an unconfined groundwater system

The seasonal changes in the concentration of uranium in an unconfined groundwater system in Cyprus have been investigated and compared to corresponding changes of boron and salinity, to better understand the chemical behavior of uranium in the respective system. Uranium concentration measurements were performed by alpha spectroscopy after selective pre-concentration, whereas boron concentration analysis and electrical conductivity measurements were carried out by photometry using azomethine-H and an electrical conductivity electrode, respectively. The experimental data show that seasonal variations are mainly related to rainwater infiltration and the specific chemical behavior of a species. Increased levels of uranium and boron in natural water systems are attributed to the increased stability of the uranium(VI)-carbonato complexes and the boric acid, which are in natural waters the predominant chemical species for uranium and boron, respectively. Dilution/dissolution processes govern the seasonal concentration changes of uranium and boron in a groundwater system, however redox-reactions resulting in the reduction of U(VI) to U(IV) affect significantly the concentration of uranium in the respective system, particularly under suboxic conditions.     

INAA analysis of fish homogenate: IAEA-436 and IAEA-407

Detailed investigations have been carried out on the well-known method of spectrophotometric determination of boron particularly in uranium compounds as boron-curcumin complex after extraction into 2-ethyl hexane 1,3-diol (EHD) to understand a number of parameters, which have not been addressed earlier in the literature. These include (i) effect of different acid media on analytical results of boron which are employed for dissolution of nuclear fuel samples, (ii) effect of diluents namely ethyl alcohol and N,N-dimethyl formamide on sensitivity of method which are employed for final dilution, and (iii) studies on loss of boron, if any, during conversion of uranium compounds to U₃O₈. Based on the present studies, the existing procedure has been suitably modified to improve the sensitivity in the measurements. In addition, this paper also describes about interference studies with Al, Cr, Mg, Ca, Fe, Mn, Mo, F⁻ and W and amount of EHD on modified method. Absolute detection limit was found to be 10 ng. The precision and accuracy of the method, is 3% at level 100 ng·g⁻¹ of boron.     

Preatomization behaviour of Se(-II), Se(IV), and Se(VI) in the graphite furnace without and with matrix modifiers

Summary Using ⁷⁵Se as a radiotracer, the preatomization behaviour of selenium in the graphite furnace was studied. The selenium forms investigated included Se(-II)-methionine, selenite, and selenate in a 0.2% HNO₃ solution, and in a 0.2% HNO₃ solution containing 1% NaCl. The effect of nickel nitrate and of the mixture of palladium/magnesium nitrates as matrix modifiers and of boron nitride coating of the graphite tube on the behaviour of selenium was investigated. The best stabilization effect for all oxidation states of selenium in the conventional graphite tube was achieved by using the mixture Pd/Mg. A considerable degree of modifier-free stabilization of selenuium could be achieved in boron nitride coated tubes. After the conversion of Se(IV) to a volatile piaselenol, a quantitative preatomization separation of Se(IV) from Se(VI) in the boron nitride coated tube was possible. However problems with these newtype tubes still to be solved include the need to increase the thermal stability of the coating.     

激光-时间分辨荧光法测定U3O8中痕量硼

本文提出了一种测定U3O8中痕量硼的激光-时间分辨荧光法, 在适当介质中, 用小型氮分子激光器激发硼与二苯甲酰基甲烷配合物的荧光, 发现此配合物的荧光寿命为2ms, 它比铀的荧光寿命长得多, 从而可将荧光的时间分辨技术应用于铀中硼的测定, 不经分离基体铀即可进行测定, 方法简单而快速, 检测下限达到0.02ng.mL^-^1(硼),当取样10mg铀时, 能测定0.01ppm的硼。用本法分析了含量在0.04-0.5ppm几个U3O8样品, 结果与其他方法相符。     

Radiographic methods for elemental analysis of boron,lithium, radium,uranium and thorium in minerals and rocks

The feasibility is discussed of applying different radiation sources for f-radiography, (n, α)-radiography and autoradiography for the determination of the spatial distribution, and the local and total concentrations of boron, lithium, radium, uranium and thorium in various materials, achieving high sensitivity and accuracy. Results demonstrating the application of the developed methods of radiography in geological practice are presented.     

杯芳烃涂层毛细管分离单胺类神经递质

本文设计制作了一种对烯丙基杯 [4 ]芳烃涂层毛细管。用于毛细管电泳分离的结果表明 ,此管能分离 5 羟色胺 ( 5 HT)、多巴胺 (DA)、去甲肾上腺素 (NE)、肾上腺素 (E)等结构相近的单胺类神经递质 ,而无涂层管则不能。本涂层管在pH4～ 9范围内的电渗较无涂层管下降约 75% ,且当pH <8时 ,电渗随pH的变化接近于线性关系 ,有利于高重现分离。杯芳烃涂层毛细管不降低紫外检测灵敏度。其主要问题是酚羟基对胺类仍有吸附 (或静电 )作用     

The extraction of uranium from acidic solutions by Adogen impregnated open cell polyurethane foam sponge

Open cell polyurethane foam coated with long chain tertiary amines (Adogen) has been shown to be an effective extractant for uranium in acidic solutions (3>pH>1). With dodecyl alcohol present uranium extraction at pH<1 is effective. The coated foam allowed column flow extraction at high flow rates but capacity studies indicated that only a fraction (about 1/3 to 1/2) of the amine was available for the complexation of the uranium. Interference of some common metal cations indicated that only Co(II) showed a significant adverse effect on the uranium extraction.     

Comparison of uncoated, pyro-coated and totally pyrolytic graphite tubes for the HGA-500 electrothermal atomiser

The analytical performance of three uncoated electrographite tubes, three pyro-coated electrographite tubes, one tantalum carbide (TaC) coated electrographite tube, and three totally pyrolytic graphite (TPG) tubes has been evaluated and compared. A test programme was devised to determine the useful operational lifetime of each tube, and assess the influence of tube age on the sensitivity of lead, manganese and vanadium measurements by atomic absorption spectrometry. The TPG tubes were found to be more durable than the other types studied, but the lifetime advantage depended on the thickness of the pyrolytic graphite. The best TPG tube, of 720 μm wall-thickness, lasted 2.5 times longer than the pyro-coated tubes, and 5 times longer than the uncoated electrographite tubes.The TPG tubes gave slightly poorer AAS sensitivity for lead, equivalent sensitivity for manganese, and 4 times better sensitivity for vanadium than the pyro-coated electrographite tubes. Also, with TPG, signal magnitude was more consistent throughout the lifetime of a tube. For each of the test elements studied, poorest sensitivity was encountered with the TaC-coated electrographite tube.     

Iridium and Rhodium as Permanent Chemical Modifiers for the Determination of Ag, As, Bi, Cd, and Sb by Electrothermal Atomic Absorption Spectrometry

Performance of graphite platforms coated with Ir, Rh, and a mixture of both, as permanent modifiers for Ag, As, Bi, Cd, and Sb, was evaluated. The coating process is very simple: a solution containing Ir, Rh, or a mixture of both is pipetted on the platform inserted in a graphite tube, and this is submitted to a temperature program. High pyrolysis temperatures are allowed, especially for As and Bi, 1400°C, in the Ir + Rh-coated platform. The sensitivity remains about the same for all analytes with different coatings, except for As in the Ir-coated platform, for which a remarkable gain was obtained in comparison to the other coatings. The lifetimes of the treated tubes were in the range 50 to more than 1000 cycles, being especially long for Sb and Ag in the Rh-coated platform, more than 600 and 1000 cycles, respectively. The Rh coating could not be used for Bi and Cd. Analysis of a certified reference water and of acid oyster tissue digests showed the absence of interference and good precision. Advantages of the permanent coatings are the possibility of low blanks byin situcleaning of the modifier and shorter analysis time.     

Change of Boron Substitution Improves the Lasing Performance of Bodipy Dyes: A Mechanistic Rationalisation

Bodipy laser dyes are highly efficient but degrade rapidly in solution by reacting with in situ generated singlet oxygen (¹O₂). To increase the lasing lifetimes of these dyes, we have designed and synthesised two different congeners of the widely studied Pyrromethene 567 (PM567) by substitution at the boron centre and/or at both the boron centre and the meso position. The two new dyes showed high lasing efficiencies with increased photostability. The results of theoretical and pulse radiolysis studies revealed that the substitution at the boron centre reduced the ¹O₂ generation capacity of these dyes as well as their rate of reaction with ¹O₂, thereby enhancing their lifetimes even under lasing conditions.     

Charge strippers for Radioisotope Beam Factory at RIKEN

The accelerator complex at the RIKEN Radioisotope Beam Factory accelerates heavy ions ranging from oxygen to uranium using triple stripping system to provide the beams at required charge. In many cases, the charge strippers cause problems during high-intensity beams accelerator operation. The charge stripper problem has been most significant during uranium beam acceleration because the lifetimes of the conventional carbon foils are extremely short. We conducted extensive R&D on the first stripper and found a solution using a low-Z gas stripper. We also plan to modify a second stripper operating recently with short-lifetime carbon foils. The stripper with better parameters will be needed when the beam intensity is increased by a new injector system for acceleration of uranium beam with higher charge.     

Boltwoodite [K(UO2)(SiO3OH)(H2O)1.5] and compreignacite K2[(UO2)3O2(OH)3]2.7H2O characterized by laser fluorescence spectroscopy

Synthetically prepared boltwoodite and compreignacite were characterized with time-resolved laser-induced fluorescence spectroscopy (TRLFS). The obtained TRLFS emission spectra of both synthesized uranium minerals differ from each other in their positions of the vibronic peak maxima and in their fluorescence lifetimes. Also, the shapes of the spectra and their respective intensities are different. The TRLFS-spectrum of boltwoodite showed well-resolved sharp vibronic peaks at 485.1, 501.5, 521.2, 543.0, 567.4, and 591.4nm with deep notches between them and compreignacite is characterized by two broad peaks with various shoulders. Here five emission bands were identified at 500.7, 516.1, 532.4, 554.3, and 579.6nm. The shape of the TRLFS spectra of compreignacite is typical for uranium in a hydroxide coordination environment. For both minerals two fluorescence lifetimes were extracted. The two species of boltwoodite and compreignacite, respectively, showed the same positions of the peak maxima showing that the coordination environments are similar, but differ in the chemistry and number of possible quenchers, e.g. water molecules and hydroxide groups. For boltwoodite fluorescence lifetimes of 382 and 2130ns, and for compreignacite shorter ones of 202 and 914ns, respectively, were determined. The spectroscopic signatures of the two uranyl minerals reported here could be useful for identifying uranyl(VI) mineral species as colloids, as thin coatings on minerals, as minor component in soils, or as alteration products of nuclear waste.     

Determination of ultratrace boron concentrations in uranium oxide by isotope dilution-thermal ionization mass spectrometry using a simplified separation procedure

Boron was determined at sub-ppm levels in uranium oxide by ID-TIMS. Following nitric acid dissolution, a solvent extraction method was adapted for extraction of boron by 5% 2-ethylhexane-1,3-diol in chloroform followed by evaporation of the extractant in presence of sodium carbonate and mannitol. This procedure allowed TIMS analysis of boron by monitoring the Na₂BO ₂ ⁺ ions formed from the sodium borate salt in the ion source. Reproducibility of about 1% was obtained for boron determination in the three different uranium oxide samples containing sub-ppm amounts of boron.     

A comparison of the electrochemical stabilities of metal,polymer and graphite coated nanospray emitters

Chronoamperometry (CA) and cyclic voltammetry (CV) were used to compare the electrochemical behavior of metal, polymer and graphite coated nanospray emitters. It is shown that electrochemical reactions occurring at the emitter surface limit the lifetime of the noble metal coated nanospray emitters while the graphite coated nanospray emitters show good electrochemical stabilities. Although the surface of the graphite coated emitters may be passivated at positive potentials, the conductive coating is not lost as for the noble metal coated nanospray emitters. The graphite coated nanospray emitters still produced a stable nanospray signal despite the presence of a passivated surface. The polymer (i.e. polyaniline) coated nanospray emitters showed very low electrochemical activity and could not be thoroughly tested by CA. The relative short lifetimes seen in the electrochemical tests are qualitatively comparable with those obtained in nanospray experiments, in which only the outmost tip of the emitter is electrochemically active. However, the electrochemical stress during CA far exceeds the stress during ESI, which implies that CA can be used to perform quick and simple estimates of emitter stabilities. To our knowledge, this is the first time the electrochemical behavior of metal, polymer and graphite coated nanospray emitters has been compared.     

Charcoal open tubular traps for the analysis of air and headspace samples

5 cm × 0.3 mm i.d. glass capillary tubes coated with fine charcoal particles are used for the analysis of organic compounds, particularly tri- and tetrachloroethylene, benzene, and toluene, in air and headspace samples. Due to their small size, these traps are easy to use with capillary GC. As, e.g. 20 ml of gas can be sucked through this trap in 20 s, it is a simple technique providing high sensitivity; compared to headspace with split injection, sensitivity is increased by a factor exceeding 100. The column effluent is split into FID and ECD in such a way that small as well as large amounts of the chlorinated compounds can be detected.     

The effects of boron and lithium on the ratio of induced to spontaneous fission in natural uranium

The presence of boron and lithium in natural uranium systems in altering the ratio of induced fission of ²³⁵U is significant. For systems containing 0.06% boron and 0.038% lithium with respect to uranium (low Z/U atom to atom ratio equals 1.32 × 10⁻²), the induced to spontaneous fission ratios were measured to be 1.4 and 0.60 respectively. The increase in the neutron flux is attributed to (α, n) reactions on the low Z elements present in the systems.     

杯芳烃涂层毛细管的制备与电泳性能考察

通过化学键合的方法制备杯芳烃涂层毛细管,并用几种苯酚取代物对其电泳性能进行了考察。结果表明,该涂层管具有特殊的分离选择性,良好的稳定性和较高的检测灵敏度等特点。     

Application of laser-induced fluorescence for determination of trace uranium, europium and samarium

Trace amounts of uranium, europium and samarium can be determined by means of laser-induced fluorescence. The fluorescence emission and excitation spectra were observed by adding fluorescence enhancing reagents. The fluorescence lifetimes of these elements were also measured. The intensities of emission were found to be linear with respect to the concentration of the element over a wide range. The detection limits for U(VI), Eu(III), and Sm(III) were established as 0.05, 0.1, and 10 ng/ml, respectively. The study suggested that this is a suitable technique for the trace determination of uranium and rare earth elements.     

Selective Detection of Dopamine and Its Metabolite,DOPAC, in the Presence of Ascorbic Acid Using Diamond Electrode Modified by the Polymer Film

The surface of boron‐doped diamond (BDD) electrode is modified by the polymer film for the first time. The cationic polymer film of N,N‐dimethylaniline (DMA) is electrochemically deposited on BDD electrode surface. This polymer (PDMA) film‐coated BDD electrode is used as a sensor which selectively detect dopamine (DA) in the presence of ascorbic acid (AA). This electrode also can detect both DA and its metabolite, 3,4‐dihydroxy phenyl acetic acid (DOPAC) in the presence of AA in the range of the physiological concentrations of these species. Favorable ionic interaction (i.e., electrostatic attraction) between the PDMA film and AA or DOPAC lowers their oxidation potentials and enhances the current response for AA and DOPAC compared to that at the bare electrode. The PDMA film also shows a hydrophobic interaction with DA and DOPAC. In cyclic voltammetric measurements, the PDMA film‐coated electrode can successfully separate the oxidation potentials for AA and DA coexisting in the same solution and the separation is about 200 mV. AA oxidizes at more negative potential than DA. In square‐wave voltammetry, the sensitivity of the PDMA film‐coated BDD electrode for DA in the presence of higher concentration of AA is higher than that of the PDMA film‐coated glassy carbon electrode. The hydrodynamic amperometric experiments confirm that the oxidation of AA is not affected by the oxidized product of DA and vice versa. So, unlike the bare electrode the catalytic oxidation of AA by the oxidized DA is eliminated at the PDMA film‐coated BDD electrode. The sensitivities of the modified electrode for AA, DA and DOPAC, which are present in the same solution with their physiological concentration ratios, are calculated to be 0.070, 0.363 and 0.084 μA μM^?1, respectively. The modified electrode exhibits a stable and sensitive response to DA.