Gábor Galbács

Use of the Ar2+ signal as a diagnostic tool in solid sampling electrothermal vaporization inductively coupled plasma mass spectrometry

The utility of the Ar2+ signal (at mass-to-charge ratio m/z= 80) as a diagnostic tool in solid sampling electrothermal vaporization inductively coupled plasma mass spectrometry (ETV–ICP-MS) is reported. Simultaneous monitoring of the argon dimer signal with the signal(s) of the analyte element(s) indicated that non-spectral interferences, caused by matrix components co-volatilizing with the analyte element(s), can strongly affect the analyte signal profiles in solid sampling ETV–ICP-MS of samples of biological or environmental origin. This observation led to a more profound understanding of why, for a given matrix, the signal profiles strongly differ from one element to another, and why, for a given element, the signal profile is seen to be strongly dependent on the matrix. These matrix effects were also observed to cause a curvature in the sample mass response curves (analyte signal intensity as a function of sample mass). It is shown that, at least in some instances, the use of the Ar2+ signal as an internal standard allows (i) this non-linearity to be corrected for and (ii) accurate analysis results to be obtained. Finally, it is demonstrated that simultaneous registration of the argon dimer and the analyte signal(s) is useful during optimization of ashing and vaporization temperatures.

Mechanical and chemical breaking of multiwalled carbon nanotubes

Catalytically prepared multiwall carbon nanotubes (MWNTs) were cut and functionalised by mechanical and/or chemical methods. Products were characterised by transmission electron microscopy, infrared spectroscopy and BET method. It can be concluded that physical and chemical breaking procedures complete each other very well. With certain MWNT samples containing surface oxides preliminary investigations were done for testing them as catalyst support.

Magnetic iron oxide/clay composites : effect of the layer silicate support on the microstructure and phase formation of magnetic nanoparticles

Magnetic iron oxide nanoparticles were synthesized on two different clay supports: natural montmorillonite and synthetic laponite. The nanocomposites obtained, characterized by inductively coupled plasma atomic emission spectroscopy (ICP-AES), x-ray diffraction (XRD), transmission electron microscopy (TEM), N2 adsorption, small-angle x-ray scattering (SAXS), vibrating sample magnetometry and M?ssbauer spectroscopy, were found to exhibit highly different physicochemical properties despite their similar iron content. The observed size effect of the layered silicate support, resulting in the high abundance of very small particles (diameter of 1?5?nm) on laponite, was explained in terms of the difference between the surface charge densities and the lamellar dimensions of the clay substrates. Moreover, it was revealed that the nature of the layered support greatly affected the nanostructure (fractal dimensions, surface area, porosity) of the formed hybrid solids as well as the phase formation of iron oxide crystals. The high surface area laponite composites, due to the dominance of very small iron oxide particles, exhibited more pronounced superparamagnetic behaviour as compared to the montmorillonite samples prepared under identical conditions. The observed higher saturation magnetization of the laponite composites, attributed to their lower content in the antiferromagnetic hematite and to the onset of superferromagnetism in the aggregated particles, shows their excellent utility for adsorption/magnetic separation.

A Review of Applications and Experimental Improvements Related to Diode Laser Atomic Spectroscopy

Abstract This article attempts to review the major advancements made in the past 12 years, since 1993, in the field of diode laser atomic spectroscopy. The discussion covers experimental improvements (e.g., wavelength stabilization, frequency upconversion, enhancement of tuning characteristics, spectral bandwidth using external cavities, etc.), diagnostic applications in various atomizers, as well as analytical applications (e.g., absorption, fluorescence, and ionization spectroscopy; element‐selective detectors for chromatography; etc.). With potential new users of these methods in mind, a detailed overview of the properties relevant to atomic spectroscopy of commercial diode lasers is also given.

A study of ablation, spatial, and temporal characteristics of laser-induced plasmas generated by multiple collinear pulses.

Multi-pulse laser-induced breakdown spectroscopy (LIBS) in the collinear pulse configuration with time-integrating detection was performed on metallic samples in ambient air in an effort to clarify the contributing processes responsible for the signal enhancement observed in comparison with single-pulse excitation. Complementary experiments were also carried out on another LIBS setup using detection by an imaging spectrograph with high time resolution. The effects of laser bursts consisting of up to seven ns-range pulses from Nd-doped solid-state lasers operating at their fundamental wavelength and separated by 8.5–50 μs time gaps was studied. The ablation and emission characteristics of the generated plasmas were investigated using light profilometry, microscopy, plasma imaging, emission distribution mapping, time-resolved line emission monitoring, and plasma temperature calculations. The experimental data suggest that the two contributing processes mainly responsible for the signal enhancement effect are the plume reheating caused by the sequential laser pulses and, more dominantly, the increased material ablation attributed to the lower breakdown threshold for the preheated (molten) sample surface and/or the reduced background gas pressure behind the shockwave of preceding pulses.

Chloroplastic glutamine synthetase is activated by direct binding of aluminium

Acidification of soils may release water soluble, toxic aluminium species from clay minerals. Al interferes with a wide range of physical and cellular processes. Glutamine synthetase (GS, EC 6.3.1.2) is the key enzyme of primary N assimilation, as well as ammonia reassimilation and detoxification. Plant GS requires two magnesium ions per subunit for activity, which makes GS a potential target of metal stress. The objective of this investigation was to prove that Al from an organic metal complex is able to activate GS, and Al becomes bound to the polypeptide structure of the GS molecule. Aluminium(III)-nitrilotriacetic acid complex (Al(III)NTA) activated the GS prepared from wheat (Triticum aestivum L.) leaves, as Al(3+) did in vivo, but could not functionally substitute magnesium ions, which were also necessary for the activity in the in vitro GS assay. GS2 was isolated by non-denaturing polyacrylamide gel electrophoresis, and the Al and Mg content of the enzyme was determined by inductively coupled plasma atomic emission spectroscopy. The GS octamer remained intact and contained Mg(2+) bound to its specific sites after the electrophoretic separation. Al was detected in the Al(III)NTA-treated sample bound to the structure of the enzyme protein, potentially occupying one of the specific metal-binding sites of the subunits. Our results indicate that the activatory effect of the Al(III)NTA complex is because of specific binding of aluminium to the polypeptide chain of GS2, however presence of magnesium at least on one of the metal-binding sites is essential to the active state of the enzyme.

Multi-pulse laser-induced plasma spectroscopy using a single laser source and a compact spectrometer

A portable laser induced breakdown spectrometer (LIBS), built around a microscope using a Q-switched Nd:GGG laser releasing multiple pulses and a non-intensified fiber optic spectrometer, was used to investigate the signal improvement of emission data achievable by the multiple-pulse approach. LIBS experiments were carried out in air and using Al, Cu, Si and Zn metallic targets. It was found that the use of 7 laser pulses, separated by ca. 25 μs time intervals, enhance line emissions by a factor of 2.5 to 129 with respect to the single-pulse case, and also decrease the relative standard deviation of the signal based on five consecutive measurements to 2–5%. Time-resolved emission data and the observation of ablation craters suggest that the signal enhancement is mainly attributable to the reheating of the plasma by multiple laser pulses.

Mass spectrometric studies of thermal decomposition products of reference materials for use in solid sampling atomic spectrometry

Gaseous decomposition products released from reference materials of plant, soil, sediment and sludge origin were identified by mass spectrometry when heated up to 15008C in a thermoanalytical furnace. Simultaneously, thermogravimetric, differential thermogravimetric and differential calorimetric measurements were also made, applying a heating rate of 208C min -1 to sample masses of 5‐10 mg. Combined thermoanalytical curves, indicating also the species evolved, are presented for ten reference samples, and cumulative mass loss data are tabulated for selected temperature limits. Utilization of the thermal data for the optimization of the solid sampling electrothermal vaporization (SS‐ETV) sample introduction method is exemplified for inductively coupled plasma optical and mass spectrometry (ICP‐AES/MS) of organic and inorganic samples. q 1998 Elsevier Science B.V. All rights reserved

Effects of continuous low-dose exposure to organic and inorganic mercury during development on epileptogenicity in rats.

The effects of chronic, low-dose fetal and lactational organic (MeHgCl) and inorganic (HgCl2) mercury intoxication on epileptogenicity were investigated and compared in rats. The main observations after both mercury treatments were a facilitated seizure expression and propagation evoked by 4-aminopyridine (4-AP). The seizure susceptibility of the offspring seemed to be in a parallel relation to the mercury concentration in the cortical tissue, which was significantly higher in treated animals as compared to the controls. While MeHgCl enhanced the number of ictal periods, HgCl2 facilitated the duration of seizure discharges in younger animals. HgCl2 intoxication seemed to be more permanent than MeHgCl. Changes in the summated ictal activity--which is an indication of epileptogenicity--were observed in the opposite directions in the two treated groups with increasing age. The amplitudes of seizure discharges were smaller in both mercury-treated groups than in the controls, which could be a consequence of a depressed proliferation of neurons or enhanced cell death in the neocortex. In summary, we observed that adult rats exposed to organic or inorganic mercury chemicals during their embryonic life, are more prone to epilepsy than control rats given only 4-AP.

A pH-Metric, UV, NMR, and X-ray Crystallographic Study on Arsenous Acid Reacting with Dithioerythritol

The aqueous solutions of arsenous acid with the meso and racemic forms of 1,4-dithiol-butane-2,3-diol, namely, dithioerythritol (dte) and dithiothreitol (dtt), respectively, were titrated pH-metrically in different molar ratios. The p K a values determined for As(OH) 3, and dtt were in good accordance with the literature data, and we determined for the first time the p K a value of dte. The deprotonation steps of both M (As(OH) 3 considered as a central metal ion) and H 2L components dte and dtt (considered as ligands) appeared at a higher pH in the titration curves of the ternary systems (M, H 2L, H (+)) than in the individual component. This unusual observation is explained by the condensation reactions between the reagents taking place in the pH < 8 range. In the solutions of c As(III) > 5.10 (-3) M, the precipitate formed upon mixing the arsenous acid and H 2L solutions in neutral medium, and the formation of the precipitate shifted toward acidic pH on the increase of the total concentrations. This indicated that pH-metry can follow the reactions only in an indirect way. Useful, but not satisfactory, information can be obtained by means of this method alone. Combined with NMR and UV spectroscopic measurements it is revealed that depending on the As(III)/H 2L molar ratio, different complexes form in the solutions. In the species with 1:2 composition, one of the ligands is strongly bound to the arsenic(III) probably via its two thiolate, while the second one is attached only weakly. The crystal structure of an As(III)-dte crystal of 1:1 composition, grown from ethanolic solution, shows that As(III) binds the ligand through its three p-orbitals in a manner similar to that expected in aqueous solution. While the uptake of the second ligand cannot be detected by pH-metry, the decomposition of thioether bonds above pH approximately 10 is confirmed by the change in UV spectra at approximately 265 nm to be a base-consuming process. In such alkaline solutions, most probably, rearrangement of the bonding scheme occurs, resulting in ligands being bound to the arsenic(III) through the oxygen donor atoms.