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The optimum conditions necessary for the determination of trace elements in organic based materials by ICP-MS are discussed. Problems experienced with condensation of particulate carbon on the sampler orifice have been eliminated by the use of a low flow of oxygen introduced into the nebuliser gas and controlled by a mass flow controller. The background spectra obtained are composed of a few simple molecular mass ions at low mass ( 80 a.m.u.). These degrade detection limits for a few elements, however the problem of blank contamination in the commonly used solvents is seen as the limiting factor in detection power. Detection limits are in general below ng ml –1 levels however for most elements, comparable to those reported for a similar system running aqueous solutions.

The analytical performance of two sample introduction-torch configurations for inductively coupled plasma atomic emission spectrometry has been optimised using the variable step-size simplex method and signal to background ratio as the criterion of merit. Small but significant improvements in limits of detection were obtained. When the two systems were compared the diameter of the torch injector tube was shown to be vital. The use of a larger bore injector (2 mm i.d.) gave rise to a smaller, more compact plasma with less variation of optimum conditions between elements. The use of a larger bore injector is therefore recommended for multi-element compromise conditions.

The first page of this article is displayed as the abstract.

A comparison of the analytical performance of five cloud chambers of different geometry used in conjunction with a commercial concentric glass nebuliser is reported. The comparison was based on measurements of transport efficiency, background equivalent concentration, analyte emission stability, detection limit, equilibration time and memory effect. Significant variations in performance indicated the importance of cloud chamber geometry on the nebulisation system. Best results were obtained with a new design based on a cylindrical chamber with a central tangential inlet. Droplet size distribution measurements revealed that although the primary distribution of the nebuliser aerosol contained a substantial proportion of small droplets of similar size to those in the ultimate distributions of the nebulisation systems, a large number of droplets are removed from the aerosol by separation processes occurring in the chambers.

Arrhenius plots were prepared from signals obtained for the atomisation of Pb, Bi and Au from a graphite surface at atmospheric pressure and in vacuum at 10 –9 atm. Spatially integrated absorbance was recorded for atmospheric pressure studies and mass spectral intensity for vacuum runs. Comparison of activation energies ( E a ) calculated from the leading edges of the signals showed no significant differences between atmospheric and vacuum vaporisation. The E a values are thus not influenced by potential radial inhomogeneities in the vapour densities within the tube. For the elements and conditions used in this study, Arrhenius data support a vaporisation model that assumes the analyte to be present on the graphite surface in the form of microparticles as opposed to a monolayer.

The first page of this article is displayed as the abstract.

The first page of this article is displayed as the abstract.

The first page of this article is displayed as the abstract.

The first page of this article is displayed as the abstract.

Radial temperature and electron number density profiles of an argon ICP have been theoretically calculated above the load coil with observation heights of from 0 to 20 mm, taking into account thermal conduction, ambipolar diffusion, collisional and radiative recombination, ionisation, axial convection, compression and expansion processes. The results of the theoretical calculations indicate that both thermal conduction and ambipolar diffusion processes are important for plasma decay above the load coil. Compression heating of the hot plasma region caused by a decrease in the temperature with an increase in observation height has a large influence on sustaining the ICP. The possible importance of a radial convection process for the peaking of temperature and electron number density towards the plasma axis, and therefore for plasma decay above the load coil, is also discussed.