Physicochemical characterisation of different welding aerosols.

Physicochemical properties important in exposure characterisation of four different welding aerosols were investigated. Particle number size distributions were determined by scanning mobility particle sizer (SMPS), mass size distributions by separation and weighing the individual size fractions of an 11-stage cascade impactor. The size distribution of the primary particles of agglomerates, chemical composition and morphology of the particles were examined by TEM. There were significant differences in the particle number size distributions of the different welding aerosols according to the SMPS determinations. The particle mass size distributions determined gravimetrically were, however, not really different. The dominant range with respect to mass was between 0.1 and 1 µm, regardless of the welding technique. Most of the primary particles in all different welding aerosols had diameters between 5 and 40 nm. All types of primary particles had a tendency to form chainlike agglomerates. A clear size dependence of the particle chemical composition was encountered in the case of manual metal arc welding aerosol. Small particles with diameters below 50 nm were mostly metal oxides in contrast to larger particles which also contained more volatile elements (e.g. potassium, fluorine, sodium, sulphur).

Prospects and problems in absolute analysis by electrothermal atomic absorption spectrometry.

The most significant achievements in the development of methods of absolute analysis in electrothermal atomic absorption spectrometry (ET AAS) made in the recent five years are discussed. Problems requiring further investigation and the significance of the concept of absolute analysis in the evolution of ET AAS are pointed out.

The effect of thermal sample pretreatment on the absorption signal in graphite furnace AAS.

The origin of the unusual maxima observed in the decomposition curves for pure solutions of some elements has been investigated theoretically and experimentally. An increase in the atom residence time caused by longitudinal redistribution of the analyte in the tube during the pyrolysis step was found to be responsible. The effect can be observed only if the sample is atomized under gas-flow conditions. To prevent any influence on analytical results, atomization should be done in the gas-stop mode.

Trace characterization of powders by atomic-absorption spectrometry: the state of the art.

A review is made of the progress achieved in the last 15 years in the field of trace characterization of powders by direct atomic-absorption spectrometry. The studies covered include the development of novel atomization devices, modification of existing atomic-absorption spectrometers, and the use of closed-cavity vaporizers. A description is given of the capsule-in-flame and circular-cavity furnace type atomizers designed on this principle, of the procedure employed in powder-sample analysis and of some analytical features of the methods used. In conclusion, various modern analytical methods are compared as to the possibilities they offer for the determination of ultratraces in solids, and suggestions are made concerning the possible role of atomic-absorption spectrometry.