Easily ionizable elements in analytical plasma pencil spectroscopy
2014
Any discharge based excitation source may suffer from some
matrix interferences. Especially easily ionizable elements from
the group of alkali metals and also alkali earths can be a
major source of these effects. Herein we present an
experimental study describing the influence of these elements
on measured spectral lines intensities and analytical results
for some selected analytes. Similarly to previous studies with
inductively coupled plasma a depression of the measured signals
occurred in most cases. A strong decrease was observed in
dependence on the concentration of the interferent while the
influence of the analyte concentration is almost negligible.
The dependence of the analyte signal decrease on the
interferent concentration is not linear. Addition of e.g.
sodium chloride causes a steep decrease of copper signal for a
relatively narrow range 0-0.2 g l-1 of NaCl. Higher NaCl
concentrations bring only moderate signal suppression. In
comparison with other lines of elements showing different
matrix effects the Na-Cu atomic interaction can be modeled by
inelastic collisions of Na-Cu excited atoms with very similar
energetic levels. The influence of the interferents on the
plasma properties was monitored by calculation of excitation
and rotational temperatures and electron number density.
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