SPATIALLY-RESOLVED MEASUREMENTS AND PLASMA TOMOGRAPHY WITH RESPECT TOTHE ROTATIONAL TEMPERATURES FOR A MICROWAVE PLASMA TORCH

To study the analyte evaporation and desolvation capacity of the micro wave plasma torch (MPT), as a new source for atomic spectrometry, the radially-resolved rotational temperatures as a good approximation for the gas-kinetic temperatures were determined. An atmospheric pressure microwave discharge in argon at a frequency of 2.45 GHz at a power of 100 W and a gas flow rate of 0.61 min(-1) was studied. The procedure m akes use of the rotational fine structure of the (A(2)Sigma(+) --> X(2 )Pi(i)) OH band at 306.4 nm and the temperatures were obtained from th e slope of a Boltzmann plot. To obtain spatially-resolved intensities and for simultaneous detection of the different rotational lines, a ch arge coupled device (CCD) combinend with a Czerny-Turner monochromator was used. The image of the axially-symmetric plasma was rotated with the aid of a three-mirror arrangement by 90 degrees and imaged onto th e entrance slit. Radially-resolved intensities were calculated by mean s of an Abel inversion and measurements at different observation heigh ts allowed complete tomography of the plasma. For the Abel inversion a nd temperature determination, an interactive Data Language (IDL) progr am was developed, which computes the results in a short time and allow s the presentation of the results as colour contour-plots. A mean temp erature of about 3600 K with an error below 10% was found under the co nditions mentioned above. Also the influence of power and water-loadin g of the carrier gas was investigated. Both were found to affect the t emperature distribution but no significant changes in the mean tempera ture could be observed in the range 70-170 W and at a water-loading of between 0.6 and 9.0 mg min(-1) of argon.