COMPARISON OF EXCITATION CONDITIONS IN ICP-OES AND THEIR USE FOR OPTIMIZED ANALYSIS Björn Knauthe, Matthias Otto TU Bergakademie Freiberg, Institute of Analytical Chemistry, 09596 Freiberg, Germany Introduction In this study it is demonstrated that determination of physical plasma properties can be carried out by means of a routine plasma spectrometer enabling prediction of optimum mesaurement conditions for analysis of metals and nonmetals. The plasma power has been varied in the practically important range from 1100 to 1700 W in combination with observation height in the plasma as well as nebulizer gas flow. Rotational temperatures, electron number densities and electron temperatures have been invesigated. Of special interest was the extension of the usually applied analytical ares to lower electron temperatures. The investigations are mainly based on the approach by H.R. Griem, Principles of Plasma Spectroscopy, Cambridge University Press, 2001. Operating parameters (PE Plasma 2000) Rf power 1100…1700 W Rf frequency 27.12 MHz Plasma gas flow 12 l/min Auxiliary gas flow 1.0 l/min Nebulizer gas flow 0.2…2.0 l/min sample pump rate 1.0 ml/min Observation height 1…20 mm Results Rotational temperatures were determined on the basis of Boltzmann plots according to: whith line strength S, wavenumber , rotational Energy Erot. As probe for the rotational temperatures several lines of OH-bands were used as given in Fig. 1. The electron density was deduced from seven Mg I lines of different excitation energy, i.e. 277.669 nm, 277.827 nm, 277,983 nm, 285.213 nm, 383.230 nm, 383.829 nm, 516.732 nm. A typical Boltzmann plot is shown in Fig. 2. The required atomic data were retrieved from the NIST data base. The good linearity of the plots enabled electron temperatures to be estimated at mean relative errors of 2 to 3%. The highest deviations were observed at low nebulizer gas flows because of the lower sample amounts reaching the plasma. The dependence of rotational temperatures and electron densities on the nebulizer gas flow and the observation height is given in Fig. 3. Also given are plots for electron temperatures at rf power values between 1100 and 1700 W (Fig. 4). Finally, the signal-to-noise ratios for elemental lines of different excitation energies could be estimated and are exemplified in Fig. 5 for the elements K, Na, Ni, Mn, P and S. Fig. 1. OH-bands as probe for estimation of rotational temperatures Fig. 2. Boltzmann plot for estimation of electron temperatures Fig. 5. Signal-to-noise ratios for element lines of different excitation energies at 1300 W Rf power Conclusions Electron temperatures are especially useful for predicting the optimum experimental conditions (areas) for the lines under consideration Rotational temperatures are important in order to guarantee approriate atomization, excitation and ionization conditions Three areas were found from the electron temperatures related to certain excitation energies : i. area of lower temperature (yellow-red) below 7000 K,  3 eV ii. area of the usual analytical area (green) at 7000 K to 9000 K, 3 to 6 eV iii. area of higher temperature (blue) at 9000 K and higher, > 6 eV The optimum areas for different lines correlate well with those of electron temperatures Predictable: Optima of detection limits for individual elements Optimum compromise detection limits for several elements Fig. 3. Rotational (top) and electron (bottomt) temperature Fig. 4. Electron temperatures at different rf power values dependences at an rf power of 1300 W.

COMPARISON OF EXCITATION CONDITIONS IN ICP-OES AND THEIR USE FOR OPTIMIZED ANALYSIS Björn Knauthe, Matthias Otto TU Bergakademie Freiberg, Institute of Analytical Chemistry, 09596 Freiberg, Germany Introduction In this study it is demonstrated that determination of physical plasma properties can be carried out by means of a routine plasma spectrometer enabling prediction of optimum mesaurement conditions for analysis of metals and nonmetals. The plasma power has been varied in the practically important range from 1100 to 1700 W in combination with observation height in the plasma as well as nebulizer gas flow. Rotational temperatures, electron number densities and electron temperatures have been invesigated. Of special interest was the extension of the usually applied analytical ares to lower electron temperatures. The investigations are mainly based on the approach by H.R. Griem, Principles of Plasma Spectroscopy, Cambridge University Press, 2001. Operating parameters (PE Plasma 2000) Rf power 1100…1700 W Rf frequency 27.12 MHz Plasma gas flow 12 l/min Auxiliary gas flow 1.0 l/min Nebulizer gas flow 0.2…2.0 l/min sample pump rate 1.0 ml/min Observation height 1…20 mm Results Rotational temperatures were determined on the basis of Boltzmann plots according to: whith line strength S, wavenumber , rotational Energy Erot. As probe for the rotational temperatures several lines of OH-bands were used as given in Fig. 1. The electron density was deduced from seven Mg I lines of different excitation energy, i.e. 277.669 nm, 277.827 nm, 277,983 nm, 285.213 nm, 383.230 nm, 383.829 nm, 516.732 nm. A typical Boltzmann plot is shown in Fig. 2. The required atomic data were retrieved from the NIST data base. The good linearity of the plots enabled electron temperatures to be estimated at mean relative errors of 2 to 3%. The highest deviations were observed at low nebulizer gas flows because of the lower sample amounts reaching the plasma. The dependence of rotational temperatures and electron densities on the nebulizer gas flow and the observation height is given in Fig. 3. Also given are plots for electron temperatures at rf power values between 1100 and 1700 W (Fig. 4). Finally, the signal-to-noise ratios for elemental lines of different excitation energies could be estimated and are exemplified in Fig. 5 for the elements K, Na, Ni, Mn, P and S. Fig. 1. OH-bands as probe for estimation of rotational temperatures Fig. 2. Boltzmann plot for estimation of electron temperatures Fig. 5. Signal-to-noise ratios for element lines of different excitation energies at 1300 W Rf power Conclusions Electron temperatures are especially useful for predicting the optimum experimental conditions (areas) for the lines under consideration Rotational temperatures are important in order to guarantee approriate atomization, excitation and ionization conditions Three areas were found from the electron temperatures related to certain excitation energies : i. area of lower temperature (yellow-red) below 7000 K,  3 eV ii. area of the usual analytical area (green) at 7000 K to 9000 K, 3 to 6 eV iii. area of higher temperature (blue) at 9000 K and higher, > 6 eV The optimum areas for different lines correlate well with those of electron temperatures Predictable: Optima of detection limits for individual elements Optimum compromise detection limits for several elements Fig. 3. Rotational (top) and electron (bottomt) temperature Fig. 4. Electron temperatures at different rf power values dependences at an rf power of 1300 W.