Capabilities of size exclusion chromatography (in off- and on-line modes) to reduce matrix effects in ICP-MS analysis of complex solutions

Abstract

The analytical capabilities of frontal size exclusion chromatography are studied using neutral polystyrene sorbents. When studying the separation of mineral acids and their salts, it is shown that clear separation of the zone of thorium ions and rare-earth elements from the following acid zone is observed on the microporous hypercrosslinked polystyrene sorbents Purolite NN-381 and MN-270. However, separation of the ions of highly charged elements (Zr, Hf, Nb, Ta) from the acid on the studied Purolite sorbents failed. Peaks of significant self-concentration appear in the zone of thorium and rare-earth element release at a concentration of 0.1 – 50 μg/liter. The factors affecting concentration of the analytes were studied. The nature and concentration of the acid, as well as concentration of the analytes, affect the concentration coefficients which attain maximum values in the solutions of nitric acid compared to hydrochloric and phosphoric acids. The degree of analyte concentration depends on the structure of internal pores and dispersion of the sorbent, as well as on the rate of solution passage through the column. Macro-components of seawater are not retained or concentrated on hypercrosslinked polystyrene. Sodium and magnesium at a concentration of 0.1 wt.% do not affect the value of the concentration factor of the target analytes. After chromatographic separation, weakly acidic fractions of the solution with concentrated ions of REE and thorium can be obtained by simple passing of a portion of the test solution through the sorbent layer for 15 – 30 min. The resulting concentrate can be directly introduced into a mass spectrometer. The possibility of combining chromatographic separation and concentration of elements and on-line ICP-MS detection is studied. Optimal conditions for on-line detection have been selected; the accuracy of the developed approach is demonstrated in the determination of rare earth elements in seawater using the spiked test.