Balazs Magyar

Calibration Studies on Dried Aerosols for LaserAblation–Inductively Coupled Plasma MassSpectrometry

A simultaneous dried solution aerosol (Mistral nebulizer/aerosol dryer) and laser-induced aerosol introduction system was used to investigate the calibration capabilities of dried solutions for LA–ICP-MS. Gas flow rates for the simultaneous systems were optimized and gave the best results with 0.5 l min -1 for the laser gas flow rate and 0.5 l min -1 for the solution gas flow rate, at which a sensitivity of 65–80% for LA compared with 1.05 l min -1 single gas flow LA–ICP-MS was maintained. The optimum temperatures for the Mistral nebulizer were 143 °C (heating) and -3 °C (cooling). Oxide formation (CeO + /Ce + ) under these conditions is less than 0.3%. Introduction of enriched 207 Pb (as a solution) and natural lead ( via LA) allows the optimization of both sample introduction systems separately. Analyses were performed on synthetic polyethylene materials, IAEA Soil-7 and CSB-1 reference standards. The RSDs on two sample pellets with five replicates each were better than 10%. Quantitative analyses for all REEs were based on In as the internal standard and Rh as the reference element. Fractionation effects of the internal standard relative to the REE were not observed.

The role of modifiers in electrothermal vaporization inductively coupled plasma mass spectrometry (ETV-ICP-MS) for the determination of B, La and U

Abstract The role of modifiers in electrothermal vaporization inductively coupled plasma mass spectrometry (ETV-ICP-MS) for the determination of refractory elements such as La or U and carbide forming elements such as B has been studied. Solutions of NH 4 F, NH 4 Cl, NH 4 Br, NaCl, NaF, NH 4 HSO 4 , (NH 4 ) 2 HPO 4 , the gaseous halogenated hydrocarbons CHF 3 and CCl 2 F 2 and HCl have been used as modifiers. The mechanism of the modifier effect and the influence of modifiers on sensitivity enhancement have been investigated. The sensitivity enhancements are great enough to achieve absolute detection limits of 2–6 pg for boron and 10 fg for La and U. The signal reproducibility is 0.5–3.0% for a concentration of 1 μg 1 −1 La and U, and 20 μg 1 −1 boron. Therefore, by adding modifiers, the use of ETV-ICP-MS can be extended to trace element determination of refractory and carbide forming elements in μl amounts of sample.

Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) for spatially resolved trace element determination of solids using an autofocus system

Abstract Laser ablation inductively coupled plasma mass spectrometry was used for spatially resolved trace element analysis of archaeological samples. An autofocus system was built in order to achieve reproducible ablation conditions. This system allows focusing of any sample automatically, with an accuracy of 10–50 μm, in the focal plane of the laser, or any height specified by the user, and can correct for surface roughness point per point. The applicability of the autofocus system is demonstrated. Trace element determination of archaeological samples with a lateral resolution of 50 μm is shown as an example. Absolute detection limits of 01–1.4 pg are achieved.

Some effects of aerosol drying and oxygen feeding on the analytical performance of an inductively coupled nitrogen-argon plasma

Abstract The determination of metals in organic solutions by atomic absorption and emission spectrometry using an inductively coupled argon plasma as atomizer (ICP-AAS and ICP-AES) is interfered by the high background emission of the plasma. This analytical problem can be mastered by the combustion of the emitting molecules, e.g. C2 and CN, and the graphite C(s) produced in the ICP. By feeding oxygen via the carrier gas flow, to achieve concentrations of 0.5% ( v v )-5% ( v v ) in the combined intermediate and carrier gas flow, the background radiation is reduced to normal levels, as obtained when aerosols of aqueous solutions are introduced. Using the slope of the calibration curves “signal-to-background ratio vs concentration” as a measure of the sensitivity, a sensitivity enhancement by a factor of 10–20 can be effected by oxgen feeding. If chloroform is used as solvent, graphite is very intensely produced in the plasma. Its combustion leads to the release of the analyte segregated in the graphite and may lead to an enhancement of the sensitivity of atomic absorption measurements by a factor of 2–5. A further enhancement of the sensitivity of determinations by ICP-AES was effected by drying the aerosols produced from aqueous and organic solutions. For this purpose a special drying apparatus was developed, in which the evaporation and the condensation of the solvent occurs in the same expansion chamber. The simultaneous use of oxygen feeding and aerosol drying produces a synergetic enhancement of the sensitivity of determination by ICP-AES. The applicability of oxygen feeding is of course limited to metals that do not give very stable monoxides. Therefore, the formation of some monoxides in the ICP was also studied.

Why not ICP as atom reservoir for AAS

Abstract The sensitivity S A of determination by inductively coupled plasma atomic absorption spectrometry (ICP—AAS) is discussed. All important factors influencing S A are comprised in one single sensitivity formula, which allows an estimate to be made of the correct order of magnitude of S A for both flame—AAS and ICP—AAS measurements. The most important analytical factors are the degree of dissociation and ionization (0≤ f C , and f I ≤1), the dilution factor f D , which takes into account the dilution of the analysis element A by its transition from the solution to the ICP, and the absorption path length b . Like flame—AAS, an analytical approach using ICP—AAS has high selectivity and makes it possible to carry out determinations without chemical and ionization interferences. This important advantage of ICP—AAS in comparison to flame—AAS is based on the fact that the ideal condition f C →1 and Δ f →0 for the analysis and standard solutions can be much more easily realized in the ICP than in flames. Serious disadvantages of an ICP as an atomic reservoir for AAS are the reduced sensitivity and lower detection power compared to flame—AAS. The reduction of S A is caused mainly by the reduction of b/f D by a factor of about 0.1 and to a smaller degree by stronger broadening of the absorption line and the depopulation of the lower energy state of the atom A that absorbs the resonance radiation. The estimated S A value for A = Ag, Al, Ca, Cd, Co, Cr, Cu, Pd and Pt agree with the corresponding experimental values to within a factor of about 3. No experimental values could be obtained for B and Si. An application field of ICP—AAS is the analysis of complex compounds that are difficult to dissociate into atoms using flames. In these determinations, a high sensitivity is generally not needed but a good selectivity is important. Some applications are shown.

Determination of metals in airborne particles by electrothermal vaporization inductively coupled plasma mass spectrometry after accumulation by electrostatic precipitation

A method to determine metals in airborne particles by electrothermal vaporization ICP-MS after sampling by electrostatic precipitation into a graphite tube is described. A mobile sampler was used to collect samples. Calibration was performed with dried aerosol produced by the nebulization of a standard solution. For Cr, Fe, Mn, Cu, Zn, Sr, Cd, Sb, Ba and Pb, the absolute detection limits were in the picogram range. The high sensitivity allowed the monitoring of several metals in ambient air with a time resolution of hours. The precision was 10–15%. The addition of 5 µg g -1 of Na (as NaNO 3 ) to the standard solutions improved the signal intensities and reduced the curvature of the calibration curves. The influence of CHF 3 was investigated but subsequently abandoned owing to a general increase not only of the signals but also of the background.

An auto-focus system for reproducible focusing in laser ablation inductively coupled plasma mass spectrometry

Abstract A method of controlling the focus position of the ablating laser was evaluated. This system consists of a displacement measuring unit based on the triangulation displacement measurement principle. A simple preliminary experimental setup with a light source (LED, light emitting diode) and a displacement-sensor (PSD, position sensing detector) with optics and a electronic circuit, resulted in a reproducibility of a given lateral position of ±5 μm. A fine-tuning of the components, as well as the use of a laser diode as a light source will certainly improve this value.

Determination of subnanomolar concentrations of tungsten(VI) by catalytic adsorption polarography

A new differential pulse polarographic method for the determination of W(VI) using a catalytic adsorption wave is described. W(VI) is first chelated by 7-iodo-8-hydroxyquinoline-5-sulfonic acid at pH 0.5. The complex ion formed is strongly adsorbed on the surface of a dropping mercury electrode. At a potential of −0.95 V versus the Ag/AgCl (3M KCl) reference electrode the adsorbed complex is reduced by the polarographic current and oxidized very fast by hydrated hydrogen ions providing the oxidized form of the complex ion for repeated redox cycles. As the redox process taking place in the electric double layer, the diffusion of the complex does not limit the polarographic current. Therefore, high currents occur, and consequently, a very high sensitivity is obtained. The practical detection limit (PDL) is 3.7 ng W/kg solution corresponding to 2 × 10−11M. The standard deviation of single values is 1.2 ng/kg at the concentration of 91 ng/kg lying in the middle of the linear part of the calibration curve. Because Mo (VI) gives a very similar catalytic adsorption wave, serious mutual interferences occur in the analysis of mixtures of both species. An effective separation of Mo(VI) was worked out. Using 1% (w/v) solution of trioctylphosphinoxide in kerosene, Mo(VI) can almost completely be extracted from 1.8M HCl with a threefold extraction resulting in a separation factor of 40000.

Equilibrium ion exchange method: methodology at low ionic strength and copper(II) complexation by dissolved organic matter in a leaf litter extract.

The equilibrium ion exchange method (EIM) is a powerful tool for the investigation of metal cation complexation by dissolved organic matter (DOM) in natural systems. Tests with different ion exchange resins demonstrated that under low ionic strength conditions (0.01 mol/kg) and in the presence of DOM, equilibration times of at least 24 h are required for experiments with Cu(II). The classical approach to the EIM was modified by using nonlinear reference adsorption isotherms in order to expand the method to a broader range of experimental conditions. For Cu(II) at low ionic strength (0.01 mol/kg), the reference isotherms between pH 4 and 6 were identical and were mathematically modeled in terms of Langmuir adsorption parameters. The EIM using nonlinear reference isotherms was validated between pH 4 and 6 by the correct determination of the stability constants for the complexes CuOxalate and Cu(Oxalate)(2). Then the method was used to quantitatively characterize the Cu(II) complexation behavior of DOM in an aqueous chestnut leaf litter extract between pH 4 and 6. In contrast to the classical approach to the EIM, data were analyzed by using plots [Cu](bound)/[Cu](free)vs. [Cu](bound). This allowed the determination of both, conditional stability constants and metal binding capacities for two different binding site classes. The logarithmic values of the stability constants were about 8 for the strong binding sites and 5.5-6 for the weak binding sites. The total Cu(II) binding capacity increased from 0.22 mol/(kg C) at pH 4 to 2.85 mol/(kg C) at pH 6.

Standardless flame atomic absorption spectrometry: problems involved in the determination of aluminium

Abstract The most important factors influencing the sensitivity of determination of aluminium by standardless (or absolute) flame atomic absorption spectrometry are the fraction atomized and the dilution factor of the analyte by its transport from the solution into the atomizer. These factors were determined as a function of the observation height and the ratio of the volume flow rates of the oxidant (nitrous oxide) and fuel (acetylene). The group of factors of dimension 1 ( G -factors) needed for the calculation of theoretical sensitivities were calculated from these fractions atomized and literature data. The theoretical and experimental G -factors are compared and their differences discussed.