Yasuaki Okamoto

High preconcentration of ultra-trace metal ions by liquid–liquid extraction using water/oil/water emulsions as liquid surfactant membranes

Abstract A high preconcentration method by liquid–liquid extraction using liquid surfactant membranes was developed. The water-in-oil (w/o) emulsion containing dilute hydrochloric acid, 2-ethylhexyl hydrogen 2-ethylhexylphosphonate (PC-88A), liquid paraffin, and kerosene was used for the extraction. In a resulting volume of 1000 cm3 of an aqueous sample solution (pH 5.0) containing less than 1 mg of each metal ion, 2 cm3 of w/o emulsion droplets coated with sorbitan monooleate were dispersed. The analyte metal ions in the outer bulk aqueous phase were extracted into the organic phase to form a complex with PC-88A and successively back-extracted into the inner aqueous phase. The analytes in the resulting inner aqueous phase were determined subsequently by graphite furnace atomic absorption spectrometry applied as a detector. By this procedure, concentration factors of 570, 820, 750, 970, 860, and 880 were achieved for chromium(III), manganese(II), cobalt(II), nickel(II), copper(II), and cadmium(II), respectively, and also the respective detection limits (3σ) of 0.4, 20, 1.2, 18, 18, and 0.7 pg cm−3 were obtained.

Zirconia-supported copper catalysts for NO[ndash ]CO reactions Surface copper species on zirconia

Cu/ZrO2 catalysts show high activity for the NO–CO reaction, even at low temperature (100–200°C). The structure and reduction behaviour of ZrO2-supported Cu species have been characterized by means of X-ray absorption near-edge structure (XANES), extended X-ray absorption fine structure (EXAFS), FTIR and temperature-programmed reduction (TPR). It was found that highly dispersed Cu2+ species in an octahedral symmetry dominated at a Cu content lower than 1 wt.% and that the amount of the Cu2+ species was saturated at 1 wt.% Cu. On the other hand, Cu oxide clusters were exclusively formed upon additional Cu incorporation after 1 wt.%. The highly dispersed Cu2+ species were produced by reaction with the terminal OH groups of the ZrO2 surface. The highly dispersed Cu2+ species were reduced by CO at a much lower temperature than Cu oxide clusters and produced highly dispersed Cu+ species at 100°C, which subsequently formed C species at 170–180°C. It is concluded that the high catalytic activity of Cu/ZrO2 for NO–CO reactions at low temperature is brought about by the formation of highly active C species on low-temperature reduction of the Cu2+ species interacting with the ZrO2 surface, and that the activity of the C species is lost by agglomeration into Cu metal particles.

Catalysis and characterization of Pd/NaY for dimethyl carbonate synthesis from methyl nitrite and CO

A vapor phase synthesis of dimethyl carbonate (DMC) from carbon monoxide and methyl nitrite (MN) has been carried out over Pd/NaY catalysts at 383 K, DMC was produced in a good yield. The selectivity to DMC was >85% on the basis of consumed CO or MN. The by-products were dimethyl oxalate, CO2, N2O, methyl formate and dimethoxymethane. The catalytic properties of Pd/NaY were investigated as a function of Pd content and calcination temperature. It was found that 1 wt.% Pd/NaY calcined at 473 K in air was the optimum catalyst for the present DMC synthesis. The oxidation state and dispersion of Pd in the Pd/NaY catalysts were characterized by EXAFS and XPS. It was revealed that Pd(NH3)42+ in 1 wt.% Pd/NaY changed into Pd metal clusters during the catalytic reaction. Pd metal clusters/NaY showed a stable activity for the DMC synthesis even after 700 h. These results suggest that the cage structure of NaY and anchoring effects of protons suppress Pd metal sintering and stabilize very small Pd metal clusters (Pd13) in the zeolite cages during the reaction.

Sensitivity enhancement for inductively-coupled plasma atomic emission spectrometry of cadmium by suction-flow on-line ion-exchange preconcentration

Abstract A column of iminodiacetate chelating resin is used to preconcentrate cadmium by a factor of 25-fold for a 5-ml sample. The sampling rate was 25 h −1 , and the detection limit 0.05 ng Cd 2+ ml −1 . The r.s.d. for 0.1 μg Cd 2+ ml −1 was 2.2% ( n = 10). This technique was applied to the determination of cadmium in certified biological reference materials and waste-water samples.

Trace ion analysis of sea water by capillary electrophoresis: determination of strontium and lithium pre-concentrated by transient isotachophoresis

The applicability of capillary zone electrophoresis (CZE) to ions having relatively low natural occurrences in sea water is limited by methods relatively poor concentration detection sensitivity. A combination of CZE with indirect UV detection and transient isotachophoresis (tITP) pre-concentration was developed to evolve the CZE practical utility towards the quantitative determination of the minor sea water cationic components, strontium and lithium. The ITP stacking criterion at the initial stage of a CZE separation was met by taking a highly mobile sodium, the principle matrix cation, to perform the role of a leading ion, whereas the moderately mobile sample macrocomponents, Ca2+ and Mg2+, acted as the terminating ion. The carrier electrolyte, consisting of 10 mM 4-methylbenzylamine and 1.5 mM citric acid at pH 4.8, was found to be optimal to accommodate both analyte cations in the ITP range and then separate them in the CZE mode, with relative standard deviations for migration times from 0.06-0.15% and for peak areas from 4-8%. The limits of detection were 1.3 mg l(-1) Sr2+ and 0.12 mg l(-1) Li+. The developed method was applied to the analysis of a surface sea water sample and a sea water reference material. The results were in good agreement with those obtained by inductively coupled plasma atomic emission spectroscopy (ICP-AES) and electrothermal atomic absorption spectrometry (ET-AAS).

Determination of vanadium and titanium in steel by inductively coupled plasma atomic emission spectrometry with modified use of a tungsten boat furnace atomizer for atomic absorption spectrometry

Abstract For electrothermal sample introduction, a commercially available tungsten boat atomizer for atomic absorption spectrometry (AAS) was transferred to a vaporizer for inductively coupled plasma atomic emission spectrometry (ICP-AES). The modification retained as much of the original design of the atomizer as possible, so that the apparatus could be switched easily between conventional tungsten boat furnace (TBF)-AAS and TBF-ICP-AES. By using this system, a procedure for the determination of vanadium and titanium in steel was investigated. The detection limits (S/N=3) of vanadium and titanium were 3.9 and 1.5 ng ml−1, respectively. The relative standard deviations for five replicate determinations were ca. 3% for both elements. The calibration graphs were linear up to 100 μg ml−1 vanadium(V) and 10 μg ml−1 titanium(IV). Results of analyses of some low-alloy steel samples are given.

Furnace-fusion system for the direct determination of cadmium in biological samples by inductively coupled plasma atomic emission spectrometry using tungsten boat furnace–sample cuvette technique

A solid sampling technique using an electrothermal vaporisation device is described. To a small sample cuvette made of tungsten, a solid mixture of a biological sample and diammonium hydrogenphosphate powder as a fusion flux was added. The cuvette was superposed on a tungsten boat furnace, then tetramethylammonium hydroxide solution was injected as a sample decomposition reagent. By resistance heating of the tungsten boat furnace, the cuvette temperature was maintained at a wet-digestion temperature sufficient to decompose the solid sample. After the on-furnace digestion was complete, the temperature was successively elevated up to maximum to generate analyte vapour. The transient cloud of vapour was introduced into the plasma. Since any solid samples could be decomposed to ash completely on the cuvette, the sensitivity was the same as that of aqueous standards. The method was successfully applied to the direct determination of cadmium in biological certified reference materials.

Electrodialysis pretreatment system for ion chromatography of strongly acidic samples and its application to the determination of magnesium and calcium

Abstract A newly developed electrodialysis pretreatment system in combination with a new dual anion-selective membrane tubes was employed to reduce the acidity of a strongly acidic sample solution prior to the ion chromatographic determination of magnesium(II) and calcium(II). By using this system, anions such as sulphate or nitrate were also removed from the sample solution through the membrane. The detection limits were 7.8 and 25 ng/ml and the upper limits of the linear response were 2 μg/ml and 5 μg/ml for magnesium(II) and calcium(II), respectively. Results of the analyses of some strongly acidic solutions are given.

A Versatile Sample Introduction System with Graphite Tube Furnace for Inductively Coupled Plasma-Atomic Emission Spectrometry

The inductively coupled plasma (ICP) has developed into a highly efficient source for atomic emission spectrometry (AES). With the demand for processing microliter, high-salt-content, and viscous solutions, the graphite tube furnace vaporization (GFV) technique shows high potential for sample introduction. Recently, commercial graphite tube furnace atomizers (GFA) for atomic absorption spectrometry (AAS) have been modified for direct electrothermal sample introduction into ICP. This note details an adaptation of a commercially available GFA to ICPAES that retained as much of the original design of the atomizer as possible, so that the apparatus could be switched easily between conventional GFA-AAS and GFV-ICPAES. The described modifications of the GFA were undertaken with two aims: to minimize the cost of conversion from GFA-AAS to GFV-ICPAES and to optimize the efficiency of introducing analyte vapor into the ICP.

Dispersion and location of molybdenum sulfides supported on zeolite for hydrodesulfurization

The dispersion and location of zeolite-supported molybdenum sulfide species have been studied by means of XAFS, XPS, XRD, HREM and pore volume measurements. The zeolites used in the present study were NaY, USY and EMT. Molybdenum sulfide catalysts were prepared by Mo(CO)6 adsorption and impregnation techniques, the former catalysts being considerably more active than the latter systems for the hydrodesulfurization of thiophene and hydrogenation of butadiene. It was demonstrated that with NaY-supported catalysts, molybdenum sulfide species derived from Mo(CO)6 were completely sulfide and highly dispersed inside the zeolite pores. The crystal structure of the host zeolite was not destroyed by the accommodation of the molybdenum sulfide species in the pores. The relative activity of the catalyst for the hydrodesulfurization of substituted thiophenes and pore volumes measured using benzene as an adsorbate were in conformity with the HREM observations that the molybdenum sulfide clusters are located inside the zeolite pores. The structure and dispersion of the molybdenum sulfide species prepared using Mo(CO)6 encaged in zeolite were shown to depend on the zeolite composition and crystal structure. Molybdenum sulfide species in the impregnation catalyst were found to be incompletely sulfide and poorly dispersed in contrast to the molybdenum sulfide catalysts prepared from Mo(CO)6.