Gerhard Schaldach

Simple low-cost tungsten-coil atomiser for electrothermal atomic absorption spectrometry

The development of a low-cost filament furnace for use with electrothermal atomic absorption spectrometry (ETAAS) is described. The filament furnace is based on the utilisation of a cheap tungsten coil originally produced with high precision for the halogen bulbs of photo-projectors. All elements determinable with a tube furnace can also be determined with the filament furnace, with the exception of Mo (an impurity of W). The elements Al, Ba, Cd, Co, Cr, Eu, Mn, Ni, Pb, Si, Sn, Ti and V were investigated in more detail. The system incorporating the filament furnace proved to be of comparable sensitivity to the system involving a commercially available graphite furnace when determining Cd, Co, Cr, Eu, Mn, Ni, Pb, Sn and V. However, Al, Si and Ti are less easy to determine compared with the graphite furnace technique. This can be explained by the steep temperature gradient on the surface of the tungsten filament. On the other hand, Ba can be determined with a higher sensitivity, by about one order of magnitude. A mixture of 90% Ar and 10% H2 was used as purge gas.The practical application of the system is shown by the determination of trace elements in synthetic urines.

Measurement of Cr(III)/Cr(VI) species by wavelength modulation diode laser flame atomic absorption spectrometry

Abstract High-performance flow atomic spectrometry of Cr(III) and Cr(VI) species by high-performance liquid chromatography (HPLC) separation, hydraulic high-pressure nebulization (HHPN) for sample introduction and wavelength modulation-laser atomic absorption spectrometry (WM-LAAS) with diode lasers in an analytical flame is reported. 3σ detection limits of 0.5 and 1 ng ml−1 have been obtained for Cr(VI) in deionized and drinking water, respectively. Due to relatively high blank levels, the corresponding detection limits of Cr(III) are higher than for Cr(VI), i.e. 1.6 ng ml−1 in deionized water and 5 ng ml−1 in drinking water.

Characterization of a cyclone spray chamber for ICP spectrometry by computer simulation

The aerosol transport and modification in a typical cyclone spray chamber for ICP spectrometry is simulated for the first time by computational fluid dynamics (CFD). Information that is not accessible experimentally can be gained, for example, about the droplet deposition at different places on the walls inside the chamber. The numerical prediction of the argon flow inside the spray chamber shows a typical swirling flow pattern, as expected in a cyclone chamber. The cyclone spray chamber works primarily like an impact chamber with regard to the deposition behaviour of the aerosol droplets, and not as a typical cyclone used in technical areas. The largest share of the nebulized sample (∼36%) is impacted directly onto the surface in front of the nebulizer. Approximately 17% is deposited on the rest of the curved surface in the plane of the nebulizer. About 29% is collected on the conical bottom, and ∼15% on the conical top of the spray-chamber, respectively. The simulation predicted a value of 2.0% for the aerosol yield at the outlet of the chamber; the experimentally determined value amounted to 2.4%. As can be seen from a comparison of the results obtained from experiment and CFD, computer simulation can be considered as a modern tool for helping to shed light on the processes occurring in spray chambers and for the prediction of their analytical performance.

Metal Speciation in the ppt Range by HPLC and Diode Laser Atomic Absorption Spectrometry in a Flame.

A simple, compact, and powerful instrument for metal speciation in the ppt range is described. The instrument includes a HPLC module for separation and a diode laser for element-selective detection by wavelength modulation absorption spectrometry in an analytical flame. The high detection power for metal species is due to a two-beam arrangement with logarithmic amplification of the normalized signal, which compensates the laser residual amplitude modulation noise, the offset, and its fluctuation. The analytical figures of merit are demonstrated by measurements of very low concentrations of Cr(VI) in tap water.

Adaptation of a new pneumatic nebulizer for sample introduction in ICP spectrometry

A new pneumatic nebulizer, the pneumatic extension nozzle (PEN), originally developed in technical laboratories, mainly for the production of rock and glass wool, is applied for sample introduction in ICP-OES. The droplet formation process under various operating conditions and geometries was investigated using a transparent enlarged model of the PEN. For the application in ICP spectrometry the geometry of the PEN was optimized and miniaturized with the aid of similarity theory. In comparison with a standard concentric nebulizer the miniaturized PEN generates an aerosol with a twice higher mass fraction of droplets with diameters D < 10 μm. An empirical model for the prediction of the mean droplet diameter is presented, using the nozzle diameter as a linear size scale. This model enables a better fit to experimental data compared with existing models. Applying the miniaturised PEN to a simultaneous ICP-OES instrument lowers the detection limits up to a factor of 3.5 depending on the element. The new pneumatic extension nozzle can be easily adapted to existing ICP-OES instruments.

An application of computational fluid dynamics (CFD) to the characterisation and optimisation of a cyclonic spray chamber for ICP-AES

This paper describes the application of computational fluid dynamics (CFD) to the modelling of the performance of a cyclonic spray chamber with flow spoiler designed to provide good efficiency with rapid wash-out time. The modelling is carried out under two flow regimes, one corresponding to typical sample introduction conditions and one to low sample uptake. Velocity distributions, pressure distributions and mass flows are simulated, the latter employing the measured primary aerosol distributions as inputs to the computation. The dynamic performance of chambers is also modelled and the signal profiles produced are shown to correspond to those derived directly from measurement. Six different chambers are studied corresponding to a chamber with no spoiler, a single spoiler in four different positions, and a chamber with 3 spoilers. The position of the spoiler is shown to be critical in determining the flow field in the chamber and hence the efficiency and washout time. It is demonstrated that chamber geometry has maximum impact under low uptake conditions where the limited dispersion primary aerosol can effectively follow the gas flow lines. Computation indicates that a chamber with optimised spoiler, operating under low uptake conditions, provides the best combination of efficiency and response time. This was confirmed by experiment in which the performance of 3 different chambers was compared, with the optimised design providing detection limits 1.5–19 better than those obtained with the chamber supplied with the ICP-AES instrument. A chamber with 3 spoilers indicates the formation of a low-volume “virtual cyclone” inside the containing walls that combines rapid washout with acceptable efficiency.

High-performance flow electrothermal atomic absorption spectrometry for on-line trace element preconcentration–matrix separation and trace element determination

With the aerosol deposition module (ADM) the samples to be analysed by electrothermal atomic absorption spectrometry (ETAAS) are carried as an aerosol into the graphite tube and deposited at about 140 °C. The ADM is normally equipped with a pneumatic nebulizer, but in this work this is replaced by a hydraulic high-pressure (HHP) nebulizer. If HHP nebulization is used to produce the aerosol, the efficiency of aerosol transport is substantially improved (maximum aerosol yield, 60%). As a high-pressure flow system is required for this type of nebulization, on-line matrix separations–trace element preconcentrations for ETAAS are also possible. The trace elements can be separated on-line from aluminium solutions (AlCl3) and determined in 4 min. Detection limits are in the ng g–1 range (as trace elements in the aluminium). In comparison with the original ADM for sample introduction, the detection power is improved by about two orders of magnitude.

Characterization of a double-pass spray chamber for ICP spectrometry by computer simulation (CFD)

Abstract Computational Fluid Dynamics (CFD) is applied to fundamental investigations on the aerosol flow and its modification in spray chambers typically used in ICP–OES spectrometry. Detailed information is gained on the flow field (argon flow), the droplet motion and on the droplet deposition at different places on the walls inside the chamber, which is not accessible experimentally. The temporal course of the calculated mass flow rate at the outlet of a double-pass Scott type spray chamber is compared with an analytical signal received from the ICP spectrometer. The shape of the calculated time-resolved mass flow corresponds well with the shape of the analytical signal. The information on the detailed functions of various types of spray chambers gained by CFD can be used for optimization of their performance.

Optimization of the geometry of a double-path spray chamber for inductively coupled plasma-atomic emission spectrometry by computer simulation and an evolutionary strategy

Abstract Computational fluid dynamics (CFD) is used to investigate the analytical performance of variously sized inductively coupled plasma (ICP)-double-path spray chambers (Scott-type) and for the optimization of the geometry of the spray chamber using an evolutionary strategy. It can be seen from the simulation of the aerosol transport in chambers of various lengths that shorter chambers have better characteristics. This result was confirmed experimentally. A higher mass flow rate at the outlet of the chamber (aerosol yield) is obtained by reducing the diameter of the inner tube and keeping the other dimensions constant. An evolutionary strategy in combination with CFD was applied in order to find the optimum geometry for this type of chamber. For the evaluation of the virtual chambers the development of a quantitative objective function was necessary. The search for the best chamber geometry was then performed by searching for the global maximum of this function. As result, a modified ICP-double-path chamber with a much better analytical performance than that of the initial one was obtained. Replacing the original chamber by the optimized one, in the same inductively coupled plasma-atomic emission spectrometry instrument, resulted in the detection limits being lowered by a factor of 2–6 depending on the element. The combination of CFD and evolutionary algorithms can be used as a new and powerful tool for the optimization of various analytical flow systems.

Computational and PIV Analysis of the Fluid Flow in a Channel With an Oscillating Finned Surface

Experimental and CFD studies were performed to investigate the kinematics of flow resulting from oscillation of a finned surface in a duct. The experiments were performed with working fluid with a kinematic viscosity of 1.8×10−6 m2 /s. A steady flow Reynolds number in the laminar range of 0 < Re < 400 was studied. The oscillation Reynolds number Reosc was between the range of 50 and 1000. Oscillation amplitude range of 0.2 mm < A < 1.0 mm together with oscillation frequency in the range of 5 Hz < f < 90 Hz were employed. The acquired images were analysed using the particle image velocimetry (PIV) software. Three experimental conditions were studied, i.e. oscillating finned surface in a fluid at rest, steady finned flow and oscillating finned flow. CFD simulations were performed using the software suit CFX11 from ANSYS GmbH, Germany. The simulation results were compared with the PIV measurements using the time averaged velocity. The results of the visualization reveal periodic recirculation eddies around the fins which enhances the fluid mixing. The flow patterns and the crossflow effects depend on the geometries of the fins and the oscillation parameters. CFD results allow for performance predictions of different geometries and flow conditions. Enhanced heat transfer was obtained at moderate flow rates when applied in cooling system. Triangular finned geometry gives better performance.Copyright