Effect of Ar on parameters of nitrogen microwave-induced plasma optical emission spectrometry

The effect of Ar content in the range of 0–100 % was studied separately in the outer, intermediate and nebulizer gas flow on the excitation temperature and electron density, the intensity of element lines and the molecular background in a N₂ microwave induced plasma. The addition of Ar to the nebulizer flow leads to an increase in the intensities of both atomic and ionic lines with total excitation energies (E_sum) 3–13 eV to 1.7 times, depending on the selected line. Addition to the outer or intermediate flow shifts the atomic-ionic equilibrium towards the formation of ions. As a result, the intensity of ionic lines (E_sum = 10–13 eV) increases up to 1.2 times, the decrease in the intensity of atomic lines (E_sum = 3–6 eV) reaches up to 20 %. The excitation temperature and electron density in the plasma did not change significantly regardless of which flow the argon was fed into. The intensity of the molecular components of the plasma background (OH, NH, NO) changes significantly when Ar is introduced into the nebulizer flow. The OH intensity increases to 1.8 times, and NH intensity increases to 1.5 times at 100 % Ar relative to pure N₂ plasma. Supplying 100 % Ar simultaneously into the intermediate and nebulizer gas flow and N₂ into the outer flow allows one to reduce the limits of detection by up to 3.3 times, depending on the selected spectral line of the element.