SIMULTANEOUS PRECONCENTRATION OF RARE EARTH ELEMENTS USING A PARTICULATE CALCIUM ALGINATE SUBSTRATE FOR THE DETERMINATION IN WATER BY ICP-MS

Analytical methods for the determination of rare earth elements (REE) in natural waters by plasma spectrochemical techniques often require sample preparation procedures for analytes preconcentration as well as for removing matrix constituents, which can induce polyatomic interferences within ICP-MS measurements. Since REE are present at very low concentrations in natural waters (from μg L-1 down to pg L-1), assorted different separation and preconcentration strategies have been proposed to enable their reliable measurements [1]. Under these premises, calcium alginate constitutes a reliable substrate for separation and simultaneous preconcentration of REE [2]. This work presents a method based on separation and simultaneous preconcentration of 14 REE (La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu) using a column packed with particulate calcium alginate substrate for the determination in water by ICP-MS. Off-line analytes preconcentration was achieved using a flow-injection system incorporating a column containing calcium alginate (< 180 μm; 300 mg). A single quadrupole ICP mass spectrometer (model 7900 Agilent Technologies, Japan) equipped with octopole reaction system (ORS4) for removing isobaric interferences through kinetic energy discrimination with He was used. Samples were processed in triplicate by loading a 100 mL test portion (pH = 5 ± 0.2), at 0.5 mL min-1 flow rate, through the column, wherein major matrix elements (e.g., alkali and alkaline earth elements) were removed and analytes were trapped. Quantitative analytes desorption was attained with 2 mL of 1.0 mol L-1 HNO3 solution, at 0.5 mL min-1, leading to enrichment factor of 50. Recoveries of the REE from a 10 ng mL-1 spiked sample ranged from 96 to 102 %, and measurement precision ranged from 2.0 to 9.0 % (n = 3) when processing 100 mL test portions.