THE EFFECT OF ADDED HYDROGEN IN ELECTROTHERMAL VAPORIZATION INDUCTIVELY-COUPLED PLASMA-ATOMIC EMISSION-SPECTROMETRY

The effect of small amounts of hydrogen added to carrier argon on atomic and ionic lines of Pb, Mn, Mg and Cr in the ICP was studied for ETV-produced aerosols. This investigation was undertaken with a view of both elucidating underlying mechanisms and improving analytical performance. The final outcome of hydrogen addition was interpreted as being determined by a combination of several hydrogen-induced processes. The hydrogen introduction via the ET vaporizer caused lowering of the analyte appearance temperatures and, as deduced from the emission signal variation with hydrogen input, induced analyte loss for the more refractory elements of Mg and especially Cr. Thus, Cr exhibited depression of the Cr I emission but enhancement of the Cr II emission owing to the predominant effect of enhanced production of excited ions with hydrogen. In general, enhanced excitation for atomic lines and enhanced production of excited ions for ionic lines are proposed to be the main causes of improved analytical performance. The potentially adverse effect of increased background continuum emission for hydrogen is compensated for by a parallel improvement in RSDs. The degree of relative improvement with hydrogen depends on the original status of the ICP with respect to the LTE and thus plasmas with poor robustness (a large departure from LTE) benefit most from hydrogen addition. It appears probable that, unlike for wet aerosol introduction, the improvement in energy transfer by hydrogen is less important in dry aerosols where major benefit is realized through increased excitation temperature and electron number density.