Removal of high-salinity matrices through polymer-complexation–ultrafiltration for the detection of trace levels of REEs using inductively coupled plasma mass spectrometry

• The water-soluble polymer polyacrylic acid was used to bind REEs and form complexes.
• The PCUF technique was applied to separate REEs from high-salinity matrices.
• A method for REEs determination with PAA-aided PCUF ICP-MS has been developed.

The polymer-complexation–ultrafiltration (PCUF) technique was applied to separate trace levels of rare earth elements (REEs), including scandium, yttrium and the lanthanides, from high-salinity matrices prior to their determination by inductively coupled plasma mass spectrometry (ICP-MS). The REEs were converted into REE–polymer complexes using the water-soluble polymer polyacrylic acid (PAA) at a specified pH, retained on the ultrafiltration membrane of centrifugal filter units, and finally eluted using diluted nitric acid to achieve separation from matrices with relatively high levels of various inorganic ions, such as sodium, potassium, calcium, magnesium, and chlorine ions. Numerous factors affecting the PCUF efficiency were optimized. The optimal conditions included the addition of 30 mg L−1 of PAA, a pH of 7.5, a reaction time of 40 min at room temperature, and 5.0 mL of 3% nitric acid (v/v) eluent. Under these conditions, the analytes were quantitatively separated and recovered, with a resulting relative standard deviation (RSD) of less than 4.0% (0.05 µg L−1, n=5) and standard addition recoveries between 89.2% (La) and 95.8% (Sm) for matrices of various salinities. The blank samples for the method ranged from 0.0003 µg L−1 (Dy) to 0.0031 µg L−1 (Sc), and the limits of quantification (LOQs, 10σ) were between 0.0006 µg L−1 (Dy) and 0.0026 µg L−1 (Sc). Furthermore, the salinity of the sample exhibited no effect on the REE–polymer complex formation process. Finally, the method was successfully applied for the determination of trace levels of dissolved Sc, Y, and lanthanides in coastal and estuarine seawater samples.

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