Assessment of the Effect of Mineral Acids and Aluminum on the Intensity of Spectral Lines of Rare Earth Elements in Atomic Emission Spectroscopy of Microwave-Induced Plasma

To obtain reliable results in the quantitative determination of rare earth elements (REE) by atomic emission spectroscopy, it is particularly important to take into account the matrix effects of the macrocomponents contained in the analyzed solutions. Analytes obtained by liquid-phase and autoclave opening of geological samples of REE ores and minerals contain significant amounts of strong mineral acids used as reagents and such macrocomponents of the samples as aluminum (aluminosilicates) and phosphorus (phosphates in apatites). Here, we studied the effects of hydrochloric, nitric, sulfuric, and orthophosphoric acids and aluminum on the relative intensity of the ion analytical lines of La, Ce, Nd, Sm, Gd, Tb, Er, and Yb in atomic emission spectroscopy of the microwave-induced plasma (AES MIP). With an increase in the acid concentration from 0 to 1 mol/L, the relative intensity of the spectral lines of all investigated REE decreased monotonically by 10–20%. The depressing effect of aluminum, which is due to a decrease in the degree of ionization of REE atoms, was much stronger and reached 70%. It was shown that the AES MIP method is not inferior to atomic emission spectroscopy of inductively coupled argon plasma in terms of the detection limits of lanthanum, cerium, gadolinium, and erbium.