Influence of analyzed solutions on the plasma pencil discharge
2012
Herein we show an influence of analyzed water solutions
containing elements in acid matrices on both the discharge
physical characteristics and the excitation capabilities. It is
well known that the presence of acids in solutions depresses
measured lines intensities. Acids viscosity can worsen the
nebulisation efficiency and the presence of acids in the
discharge together with abundant water consume a non-negligible
amount of the delivered electrical energy. These phenomena
result in a decrease of the intensities of measured atomic
emission lines of elements in the introduced solution. The
determination of the elements in acid matrices is less
sensitive than in pure water solutions. This behaviour is also
recognizable in case of the presented plasma pencil.
Experiments were realized with three single element containing
solutions. The selected elements were Cu, Mg and Zn in the
concentration range of 1 – 100 mg l-1 and the contents of 70%
nitric acid of 2, 10, 20 and 50 ml per 100 ml flask. A decrease
of the slopes of the calibration lines depends on the
particular spectral line and ranges from about 10 to 20 % for
the acid concentration change from 2 to 20 ml per 100 ml flask.
These results are supported by changes in the rotational
temperature calculated from OH radicals, excitation temperature
from a set of Ar lines and electron number density from the
Stark effect on hydrogen H beta line. Despite the sensitivity
decrease the discharge stability was not very influenced by the
presence of the acid which is in contrast to the influence of
the pure water. It was also proven that the plasma pencil is
capable of reliable determination of zinc content in a
commercial multivitamin tab in presence of other matrix
substances.
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