Bioparticles coated with an ionic liquid for the pre-concentration of rare earth elements from microwave-digested tea samples and the subsequent quantification by ETV-ICP-OES
An analytical procedure for straight-forward quantification of rare earth elements (REEs) in tea was developed. The method consists of three steps: first, dry tea powder is converted into an aqueous sample solution using a microwave-assisted digestion procedure. Then, the REEs are retained on newly designed sorbent particles and are thus effectively extracted from the sample digest. Then, the REE-loaded sorbent material is introduced into the furnace of an electro-thermal vaporization (ETV) unit. There, the core of the particles is pyrolyzed and removed in a first temperature step. Then, the REE analytes are swiftly evaporated at high temperatures, and subsequently analyzed by ICP-OES. The advantages of the method proposed here are as follows: extraction of REEs is accomplished via “dispersed particle extraction”; this avoids typical shortcomings of conventional solid-phase extraction. The analysis via ETV allows separation of the sorbent particles from the analytes in time. Thus, detrimental effects of plasma-loading are circumvented. The method was shown to provide satisfactory detection limits of typically 50 ng g−1 in the dry tea samples (3 s criterion). The method was validated by means of spike recovery experiments, and applied to the analysis of ten different tea samples from China, Japan and India, as sold in European markets.