Thermodynamic Modeling of the Composition of the Main Background Ions and Determination of Gas-Kinetic Temperature in the Normal (“Hot”) Inductively Coupled Plasma

A possibility of studying effects of the main background ions formed by the main elements of inductively coupled plasma (H, N, O, and Ar) at the working parameters of the normal (“hot”) plasma mode by thermodynamic modeling is assessed. Such ions, responsible for the strongest spectral interferences in the mass spectra are always observed upon the injection of aqueous (“wet”) sample solutions into inductively coupled plasma mass spectrometers (ICP MS). The quantitative composition of the main background ions in an ICP MS is calculated as a function of plasma temperature in the temperature range from 3000 to 8000 K using thermodynamic modeling. The results of modeling were compared with the experimental data on the measured mass spectra of the main background ions and a high degree of correlation between the theoretical and experimental results was shown. The agreement between the results of calculations the experimental data validates the thermodynamic model of thermochemical processes in an ICP MS used and its applicability to subsequent calculations in fulfilling analytical tasks. A possibility of the unambiguous assessment of gas-kinetic plasma temperature is confirmed by comparing the theoretical and experimental mass spectra of the main ICP background ions in a normal mode. It was found that the calculated and experimental data on the concentration of only NO⁺ ions do not agree with the regularities noticed for the other background ions in the normal ICP mode.