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

The application of aminothioether sorbent — 2-(1,3,5-dithiazinan-5-yl)acetic acid (DTAA) — 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 determination of REE was carried out directly in the sorption concentrate by atomic emission spectrometry with the spectrum excitation in a DC arc (arc AES). It was found that the addition of hydrofluoric acid (10 –7 g/liter) is necessary for the complete recovery of REE from hydrochloric acid solutions. Using model solutions, the conditions of sorption extraction of REE (acidity of solution, sorbent mass, sorption temperature and time) were selected. The ability of DTAA to completely extract REE under selected conditions was confirmed by analyzing real HA and TCP samples using inductively coupled plazma atomic emission spectrometry (ICP AES). The conditions for REE impurities determination, such as generator mode, current strength, exposure time, shape of the electrodes and the distance between them, weight of the sample, were selected. 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 arc discharge plazma. 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.