Matrix effects of easily ionizable elements and nitric acid in high-power microwave-induced nitrogen plasma atomic emission spectrometry

Matrix effects of Na, Ca and nitric acid in high-power microwave-induced nitrogen plasma atomic emission spectrometry were investigated with a number of atomic and ionic lines covering a wide range of energies. The plasma was sustained in an Okamoto cavity at atmospheric pressure by using nitrogen as the plasma gas as well as the nebulizer gas. Most of the atomic lines tested exhibited enhancement effects and all of the ionic lines gave suppression effects in the presence of Na and Ca. The effects decreased with increasing microwave power. There was good correlation between matrix effects, the excitation energy and energy sum of the spectral lines. The lower the excitation energy for atomic lines and the higher the energy sum for ionic lines, the stronger the matrix effects. Unlike Na and Ca, nitric acid showed suppression effect for all of the spectral lines and the effect was independent of the energy of the spectral lines and the microwave power. The effect of matrix on the excitation temperature and the electron number density was measured and the mechanism of matrix effect was discussed.