Rare Earth Element Determination by Arc Atomic Emission Spectrometry after Sorption Preconcentration from Solutions Containing Calcium and Phosphorus

The application of 2-(1,3,5-dithiazinan-5-yl)acetic acid (DTAA) as an aminothioether sorbent for the sorption concentration of rare earth elements (REE) from aqueous solutions and solutions of REE-doped hydroxyapatites (HA) and tricalcium phosphates (TCP) has been proposed. The subsequent REE determination was carried out directly in the sorption concentrate by atomic emission spectrometry with spectrum excitation in a DC arc (arc AES). It was found that the addition of hydrofluoric acid (10^–7 g/L) is necessary for the complete recovery of REE from hydrochloric acid solutions. Using model solutions, the conditions of sorption extraction of REE were selected (acidity of solution, sorbent mass, sorption temperature, and time). The ability of DTAA to completely extract REE under the selected conditions was confirmed by analyzing real HA and TCP samples using inductively coupled plasma atomic emission spectrometry (ICP AES). The conditions for determining REE impurities were selected, such as generator mode, current strength, exposure time, the shape of and distance between electrodes, and sample weight. To reduce the matrix effect, the samples were diluted with graphite powder and a carrier, NaCl, was added to the sample to improve the atomization of REE in an arc discharge plasma. The limits of determination, relative standard deviation, and error were estimated. The results of the developed approach are comparable with those obtained by ICP AES.