Silica functionalized with 2,6-pyridinedicarboxylic acid for selective preconcentration of Rare Earth elements traces before ICP-MS analysis

There are several methods for pre-concentration of Rare Earth elements (REE) before their ICP-MS determination. Most of them based on metal adsorption on solid support with further analysis of eluate. Major problem of such approach is low selectivity of the adsorbent and slow kinetic of adsorption/desorption process. Since REE can be found in groundwater or minerais in trace amount, the adsorbents must demonstrate high selectivity towards these elements. ln addition, such adsorbents shall be able to separate REE from Ba2+ ians commonly presented in solution as macro component, since ICP-MS analysis of Nd3+, Gd3+, Sm3+, and Eu3+ ians is limited on single quadrupole ICP-MS because of serious polyatomic interferences with barium matrix (such as BaO+ and BaOH+). To improve the adsorbent selectivity towards REE we proposed to use new adsorbent with covalently immobilized fragments of 2,6-pyridinedicarboxylic acid (PdCA). To ensure high kinetic characteristics of the adsorption/desorption process PdCA was immobilized on silica gel (Si02) with high surface area and large pare size. SiOrPdCA was characterized by elemental analysis, FT-IR and XPS. The concentration of surface immobilized groups (CL = 0.3 mmol/g) was determined from several independent methods, including titration, CHN elemental analysis and TGA. The adsorption properties of SiOrPdCA were investigated in static conditions for 17 different REE in a mixture, in large excess of Ba2+ and some key heavy metal ians in the pH range 2-6. SiOr PdCA demonstrates reversible adsorption and very high kinetic characteristics. Complete adsorption/desorption process was observed for 1 O min. The adsorbent 100.00 demonstrated high capacity (200 μg/g for Eu3+ ions) and strong affinity towards all REE. SiO2-PdCA quantitatively adsorbs most of REE from solution with pH>2 containing 20 μg L-1 of metais (see picture below). Ba2+ ians has no influence on REE adsorption until pH>3.5-4. The adsorbent provide high recovery (>95%) of ali REE in presence of 500-fold of Ba2+ ians at pH=3.0. Ians of Fe3+ and Cu2+ in 1600-fold caused little or no interference on the determination of REE with recovery >80%. After adsorption of Eu3+ and Tb3+ ians, SiOr PdCA demonstrates strong red and green luminescent and can be used as luminescent probes for monitoring of Eu3+ and Tb3+ ians in solution.