The analysis of ruthenium catalysts by photon-induced X-ray fluorescence using a microcomputer for data acquisition and analysis

An improved method for the determination of ruthenium in catalytic materials based on a relative fluorescence ratio factor is presented. This method employs a thin-film technique and an internal standard technique to minimize absorption and enchancement effects. The samples and standards were fluorescent with a¹⁰⁹Cd (7 mCi) annular source for 200 seconds and the data were collected and analyzed with an Apple II+ micro computer. Precision (total variation) for typical ruthenium catalysts in the range of 1–5% ruthenium was about 2%. Finally, the concentration of ruthenium in six commercial catalysts was determined for both alumina and carbon supports.Parts of this work have been funded by an international program between CONICIT (Venezuela) and NSF (United States of America).     

Developing electrodeposition techniques for preconcentration of ultra-traces of Ni, Cr and Pb prior to arc-atomic emission spectrometry determination

Electrodeposition is known to be proper for separation and preconcentration of extremely low concentrations of analytes from the bulk sample which is instrumentally very simple. In the present research, a combination of electrodeposition with arc atomic emission spectrometry (ED-AAES) method has been developed in order to improve the analytical performance of this spectrometry technique. The results show that sensitivity and detection limits by using ED-AAES were improved 1000–2000 folds over those of normal arc atomic emission spectrometry in determination of the selected elements. The detection limits for measurement of Ni, Cr and Pb were 2.56, 3.05 and 2.11 µg L^{− 1} for monodeposition and 3.31, 3.72 and 3.25 µg L^{− 1} for simultaneously deposition, respectively. The precision of determination was in the range of 2–4% RSD. Typical calibration graphs for these elements were linear up to 100 µg L^{− 1}, depending on the element and matrix.Application of this technique was also tested on determination of the studied elements in an electroplating plant's waste water. The accuracy of technique was verified by comparing the results of the waste water analysis with those of electrothermal atomic absorption spectroscopy as a reference standard method.The obtained results show that the combined technique (ED-AAES) has been progressed substantially toward the ultimate goal of direct interference-free determination of trace analysis in complex samples by AAES.     

A rapid and highly sensitive stability-indicating high-performance thin-layer chromatography technique for the determination of tedizolid phosphate with a classical univariate calibration

No high-performance thin-layer chromatography (HPTLC) techniques have been established for the determination of tedizolid phosphate (TDZP) in pharmaceutical products or physiological fluids. Therefore, a rapid and highly sensitive stability-indicating HPTLC technique has been developed for the determination of TDZP in commercial formulations with a classical univariate calibration. The HPTLC‒densitometry analysis of TDZP was carried out via chloroform‒methanol (90:10, V/V) mobile phase. The determination of TDZP was performed at the wavelength of 300 nm. The proposed HPTLC technique was linear in the range of 10‒2000 ng band^‒1. In addition, the method was found to be highly accurate (% recovery = 98.53‒101.74%), precise (%CV = 0.67‒0.91%), robust (%CV = 0.83‒0.86%), highly sensitive (LOD = 3.41 ng band^‒1, LOQ = 10.23 ng band^‒1) for the determination of TDZP. The proposed technique was also able to detect TDZP in the presence of its degradation products under various stress conditions and it can be considered as a stability-indicating method. The proposed HPTLC technique was applied for the analysis of TDZP in its commercial formulations. The TDZP contents of commercial tablets and injection were determined as 98.41% and 101.23%, respectively. These results suggested that the proposed HPTLC technique can be applied for the routine analysis of TDZP in its commercial products and newly established formulations.

     

Neutron activation analysis of traces in electrolytic zinc sulphate solutions : Part III. Simultaneous determination of tellurium,selenium, arsenic and antimony

A neutron activation analysis is described for the simultaneous determination of tellurium, selenium, arsenic and antimony in an electrolytic zinc sulphate solution. The activity induced in the tellurium was measured by means of its radioactive daughter ¹³¹I. The chemical separation of iodine was performed by extraction into carbon tetrachloride. The interference due to the fission of uranium was minimised by a preseparation of uranium. The isotope ⁷⁵Se was measured by a γ, γ-coincidcnce technique, which allowed the determination of 0.002 μg Se/ml. Selenium was chemically separated by extraction as piazselenol. Arsenic and antimony were separated by precipitation as sulphide and distillation as chloride. The isotopes ⁷⁶As and ¹²²Sb were measured γ-spectrometrically, amounts of 0.02 μg/ml being determined. The method is also suitable, although not very sensitive, for the simultaneous determination of tin and germanium.     

Synthesis of new macrocyclic rhodium(III) compounds and their utility as catalysts for the oxidation of ascorbic acid

Ten new macrocyclic Schiff base Rh(III) compounds were synthesized by treating the corresponding macrocycles with rhodium chloride in 1:1 ratio. The resulting compounds were characterized by elemental, IR, ¹H NMR, ¹³C NMR, mass, electronic spectral analysis, and their structures have been proposed. These compounds were utilized as catalysts in the development of an efficient and environmentally friendly catalytic method for the oxidation of ascorbic acid (AA) to dehydroascorbic acid (DHAA). DHAA was determined spectrophotometrically by treating with orthophenylenediamine (OPDA) and the yields were found to be in the range 72–84%. The catalytic oxidation and spectrophotometric determination methods were found to be faster and more accurate than those reported previously.     

A simple method for the determination of natural uranium and226Ra in waters and soils

A procedure for the determination of natural uranium and²²⁶Ra in waters and soils has been carried out and applied to the analysis of samples for environmental radiological monitoring.²²⁶Ra determination consists of co-precipitation with BaSO₄,²²²Rn emanation in toluene and finally liquid scintillation counting. Natural uranium is then determined by a fluorometric technique. This paper describes the method and the conditions that were tested to optimize it. The technique was found to be suitable for the analysis of surface and ground waters, samples from rivers, streams and lakes and soil samples, because of its few steps, short processing time, high recovery percentages and suitable detection limits.     

Analysis of Sub-Microgram Levels of Palladium (II) in Environmental Samples by Selective Extraction and Spectrophotometric Determination with N-p-Methoxyphenyl-2-Furylacrylohydroxamic Acid and 5-(Diethylamino)-2-(2-Pyridylazo) Phenol

Abstract

Nine new hydroxamic acids in conjunction with four pyridylazo reagents were explored for extractive separation and spectrophotometric determination of palladium in environmental samples. It was found that maximum sensitivity and selectivity was achieved by employing N-p-methoxyphenyl-2-furylacrylohydroxamic acid (MFHA) and 5-(diethylamino)-2-(2-pyridylazo) phenol (DEPAP). Palladium was first selectively extracted with MFHA in isoamyl alcohol at pH 2.7-3.5 and the extract was equilibrated with a mixture of 5 M HCl and 10^{? 3} M solution of DEPAP in ethanol. The resulting intensely green ternary complex was measured at 560 nm (σ 5.1 × 10⁴ l mole^?1 cm^?1). The extraction system is suitable for enrichment of palladium over 15 times without loss in recovery and enables determination of palladium at levels as low as 10^?4 ppm (0.1 ppb). The method tolerates the presence of a large number of diverse ions normally associated with palladium, including platinum metals, and was employed for the determination of palladium in standard catalysts, biological materials, and freshwaters.     

One-Pot Synthesis of Heterobimetallic Metal–Organic Frameworks (MOFs) for Multifunctional Catalysis

A one-pot synthesis of bimetallic metal–organic frameworks (Co/Fe-MOFs) was achieved by treating stoichiometric amounts of Fe and Co salts with 2-aminoterephthalic acid (NH₂-BDC). Monometallic Fe (catalyst A) and Co (catalyst F) were also prepared along with mixed-metal Fe/Co catalysts (B–E) by changing the Fe/Co ratio. For mixed-metal catalysts (B–E) SEM energy-dispersive X-ray (EDX) analysis confirmed the incorporation of both Fe and Co in the catalysts. However, a spindle-shaped morphology, typically known for the Fe-MIL-88B structure and confirmed by PXRD analysis, was only observed for catalysts A–D. To test the catalytic potential of mixed-metal MOFs, reduction of nitroarenes was selected as a benchmark reaction. Incorporation of Co enhanced the activity of the catalysts compared with the parent NH₂-BDC-Fe catalyst. These MOFs were also tested as electrocatalysts for the oxygen evolution reaction (OER) and the best activity was exhibited by mixed-metal Fe/Co-MOF (Fe/Co batch ratio=1). The catalyst provided a current density of 10 mA cm⁻² at 410 mV overpotential, which is comparable to the benchmark OER catalyst (i.e., RuO₂). Moreover, it showed long-term stability in 1 m KOH. In a third catalytic test, dehydrogenation of sodium borohydride showed high activity (turnover frequency=87 min⁻¹) and hydrogen generation rate (67 L min⁻¹ g⁻¹ catalyst). This is the first example of the synthesis of bimetallic MOFs as multifunctional catalysts particularly for catalytic reduction of nitroarenes and dehydrogenation reactions.     

Spectrofluorimetric Determination of Antimony

Abstract

A spectrofluorimetric procedure for the determination of micromolar concentrations of antimony(III) was devised based on its reduction of cerium(IV) to produce fluorescent cerium(III). The method was optimized and the reaction was fast enough in hydrochloric acid media without the need for iodide or osmium(VIII) as catalysts. Linear calibration graphs were obtained in the range 1-10 10^?6M. The standard deviation for determining 5 × 10^?6M antimony(III)(10 times) was 1.43 × 10^?7M and the relative error was -3.4 %. The method was applied to the determination of antimony(III) in its mixture with antimony(V), total antimony was later determined after reduction with mercury metal in deoxygenated solutions. The affect several reducing agents on the determination of antimony-was also examined.     

Determination of oxygen in gallium arsenide by3He activation analysis using substoichiometric precipitation

Distillation of fluoride as fluorosilicic acid and substoichiometric precipitation as lanthanum fluoride was studied for the determination of oxygen in gallium arsenide by³He activation analysis. Fluoride could be separated substoichiometrically with a good reproducibility by two distillations and successive precipitation with lanthanum. The oxygen concentration in gallium arsenide prepared by the horizontal Bridgman technique was 10 to 36 ppb and increased a little along the front, middle and tail portions in the crystal.     

Substoichiometric isotope dilution analysis of calcium in biological materials

A substoichiometric isotope dilution analysis was developed for the determination of calcium in biological materials. A⁴⁷Ca tracer was produced by the photonuclear reaction and purified by a chromatographic technique on a zeolite column. The appropriate conditions and the reproducibility of the substoichiometric extraction system of TTA-TBP were examined. The present method was applied for NBS-SRM's Spinach and Pine needle, and very good results with high accuracy and precision were demonstrated.     

Role of ZnNb2O6 in ZnO-promoted amorphous-Nb2O5 supported Ru catalyst for the partial hydrogenation of benzene

Ruthenium catalysts supported on zinc-promoted amorphous-niobium mixed oxides were prepared, characterized, and studied in the additive-free partial hydrogenation of benzene reaction. The amorphous matrix of Nb₂O₅ was responsible for a highly active Ru/Nb₂O₅ catalyst, although less selective than those containing zinc. The ZnO-containing supports were prepared by wet impregnation technique, followed by incipient wetness of ruthenium chloride salt. The catalysts were characterized by textural analysis, X-ray fluorescence, X-ray diffraction, H₂ chemisorption, temperature-programmed reduction (TPR), Scanning electron microscopy, H₂ temperature-programmed desorption, and X-ray photoelectron spectroscopy (XPS) of the calcined-reduced samples. Chlorine retention was observed on zinc-containing samples. An unexpected ZnNb₂O₆ oxide phase, ascribed to a selectivity increase with less activity loss, was obtained for the supports at lower temperatures than those related on the literature. A very complex electronic environment of Ru- and Zn-containing species interactions was observed by TPR. The presence of surface-reduced (Ru⁰) and partially reduced (Ru^δ+) Ru species observed by XPS justified well, respectively, the activity and selectivity achieved with every catalyst. The addition of water as a solvent resulted in very constant yield to cyclohexene, as expected, despite activity diminution due to low solubility of the reactants.     

Ir‐Catalysed Asymmetric Allylic Substitutions with Cyclometalated (Phosphoramidite)Ir Complexes—Resting States,Catalytically Active (π‐Allyl)Ir Complexes and Computational Exploration

Mechanistic aspects of allylic substitutions with iridium catalysts derived from phosphoramidites by cyclometalation were investigated. The determination of resting states by ³¹P NMR spectroscopy led to the conclusion that the cyclometalation process is reversible. A novel, one‐pot procedure for the preparation of (π‐ allyl)Ir complexes was developed, and these complexes were characterised by X‐ray crystal structure analyses and spectral data. They are fully active catalysts of the allylic substitution reaction. DFT calculations on the allyl complexes, transition states of the allylic substitution and product olefin complexes gave further mechanistic insight.     

Problems,possibilities and limitations of inductively coupled plasma atomic emission spectrometry in the determination of platinum,palladium and rhodium in samples with different matrix composition

The economic and geological importance of platinum group of elements has led to the development of analytical methods to quantify them in different types of samples. In the present paper the quantitative information for spectral interference in radial viewing 40.68 MHz inductively coupled plasma atomic emission spectrometry in the determination of Pt, Pd and Rh in the presence of complex matrix, containing Al, Ca, Fe, Mg, Mn, P and Ti as matrix constituents was obtained. The database was used for optimum line selections. By using the selected analysis lines the following detection limits in ng g^− 1 were obtained: Pt 1700, Pd-1440, Rh-900. The reached detection limits determine the possibilities and limitation of the direct ICP-AES method in the determination of Pt, Pd and Rh in geological and environmental materials. The database for spectral interferences in the presence of aluminum can be used for the determination of platinum group of elements in car catalysts.     

Catalytic test determination of copper on a solid support

A test procedure was developed for the determination of 5 × 10^?7?1 × 10^?3 M copper with the use of the copper-catalyzed reaction of the reduction of molybdophosphoric acid by thiourea on a solid support (paper). The conditions of the indicator reaction and the technique for its conduction were optimized; the pH range in which the acidity of the solution does not affect the time of the reaction was revealed. The calibration plot for the determination of copper was constructed in reaction time-pCu coordinates. The effect of different components on the rate of the indicator reaction was studied. The procedure was approved in the analysis of real and model solutions.     

Neutron activation analysis of pure uranium: Preconcentration of impurity elements

We have developed a radiochemical neutron activation analysis technique (RNAA) of pure uranium with using extraction chromatographic separation of ²³⁹Np from impurity elements in TBP-6M HNO₃ media. The estimation of influence of fission products of ²³⁵U on the results by radiochemical neutron activation analysis has been carried out. For it we have performed NAA with preconcentration of impurity elements. Experiments show that in this case the apparent concentration of Y, Zr, Mo, Cs, La, Ce, Pr, Nd exceeds the true concentration by 2500–3000 times. Therefore, determination of these elements is not possible by RNAA. This technique allowed to use the determination of 26 impurity elements with detection limit 10⁻⁵–10⁻⁹% by mass. This developed technique may be used for the determination of impurities in uranium and its compounds.     

Trace determination of lead by helium-4 activation analysis

The determination of lead via 30 MeV⁴He bombardment to produce the long-lived radioisotope²¹⁰Po was studied. The validity of the technique was tested by the analysis of a series of NBS glass samples doped with 61 different trace elements at nominal 500 to 1 ppm level concentrations. The measurement sensitivity of alpha counting with surface barrier detectors was evaluated. The detection limit was estimated at 0.1 ppm. The⁴He-activation technique coupled with -counting features a unique combination of sensitivity and accuracy for the trace determination of lead.     

Fe-N/C-TsOH催化剂应用碱性介质催化氧还原的电催化活性

通过溶剂分散热处理方法制备了一种吡咯和对甲苯磺酸(TsOH)共同修饰的碳载非贵金属复合催化剂(Fe-N/C-TsOH),并采用扫描电子显微镜(SEM)、X射线衍射(XRD)和X射线光电子能谱(XPS)对催化剂的形貌和组成成分进行表征. 借助循环伏安法(CV)和旋转圆盘技术研究了TsOH对催化剂在0.1 mol·L^-1 KOH介质中催化氧还原性能的影响. 结果表明：TsOH的存在对催化剂催化氧还原反应(ORR)的活性影响很大. 以其制备的气体扩散电极在碱性电解质溶液中催化氧还原过程时转移的电子数为3.899,远比不含TsOH修饰的催化剂催化氧还原的电子数(3.098)高. 此外,研究发现600 ℃热处理过的Fe-N/C-TsOH催化剂表现出最佳的氧还原催化性能. 相比未经热处理过的Fe-N/C-TsOH催化剂,起峰电位和-1.5 mA·cm^-2电流密度对应的电压分别向正方向移动30 和170 mV. XPS研究结果表明吡咯氮是催化剂主要活性中心,提供氧还原活性位,而TsOH加入形成的C―S_n―C和―SO_n―有利于催化剂催化氧还原活性的提高,从而使该催化剂对氧还原表现出很好的电催化性能和选择性.     

Determination of Pb in river water samples by inductively coupled plasma optical emission spectrometry after ultrasound-assisted co-precipitation with manganese dioxide

A simple and efficient procedure for separation and pre-concentration using ultrasound-assisted co-precipitation with manganese dioxide was developed for Pb determination by inductively coupled plasma optical emission spectrometry (ICP OES). The optimization process was carried out using a two-level factorial design and a Doehlert matrix. Three variables (i.e. concentration of oxidizing solution—KMnO₄, concentration of MnSO₄ solution and time of ultrasonic irradiation) were used as factors in the optimization. The recoveries, based on the analysis of spiked samples, were between 90% and 105%, and the precision was ≤ 5%. The detection limit and quantification limit for Pb determination were 3.2 and 10.7 μg L^− 1, respectively. The proposed method was applied for the determination of Pb in water samples from a river heavily polluted by industrial effluents. The recovery measured by analyte addition technique showed that the proposed pre-concentration method had good accuracy.     

NH3 TPD study and thermal behaviour of vanadium-exchanged titanium phosphates as catalysts

The ion exchange technique was employed for the preparation of VO²⁺ modified titanium phosphates as catalysts for the selective reduction of NO with NH₃. The samples were prepared by contacting with a vanadyl sulphate solution different precursor materials, amorphous, crystalline or sodium half exchanged titanium phosphate. The vanadium contents of modified phosphates were in the range 0.08–2.3 wt%. XRD and thermal analysis TG/DTA showed that vanadium loading does not cause structural modification in hydrogen titanium phosphate. A vanadyl containing phase was obtained when half sodium titanium phosphate was employed. The NH₃ TPD measurements indicated the presence of a wide distribution of NH₃ adsorbing sites with medium-high strength. Catalytic activity measurements were performed under dilute conditions. It was found that the presence of vanadium even in low amounts strongly promote the catalytic activity.