Speciation of selenium in cells by HPLC-ICP-MS after (on-chip) magnetic solid phase extraction

Elemental speciation in cells is significant for metallomics research. In this study, novel methods of (on-chip) magnetic solid phase extraction (MSPE) combined with high performance liquid chromatography (HPLC)-inductively coupled plasma mass spectrometry (ICP-MS) were proposed for selenium speciation in selenium-enriched yeast cells. An integrated microfluidic chip consisting of reaction, mixing, and extraction units was designed and fabricated for on-chip MSPE. Sulfonated polystyrene-coated magnetic nanoparticles (Fe3O4@PSS MNPs) were prepared as adsorption material for MSPE of selenoamino acids and selenopeptide. The factors affecting the extraction performance of the target selenium species by (on-chip) MSPE-HPLC-ICP-MS were systematically investigated. The analytical performance of the (on-chip) MSPE-HPLC-ICP-MS was evaluated under individual optimal conditions. The limits of detection for five target selenium species were 0.025 μg L−1 to 0.090 μg L−1 and 0.057 μg L−1 to 0.149 μg L−1 for MSPE-HPLC-ICP-MS and on-chip MSPE-HPLC-ICP-MS, respectively. The MSPE-HPLC-ICP-MS method is sensitive, fast, easy-to-operate, and economical. The on-chip MSPE-HPLC-ICP-MS method has the unique advantages of low sample consumption and high integration; thus, it is suitable for selenium speciation in a small number (∼800) of selenium-enriched yeast cells. A Certified Reference Material of SELM-1 yeast was used to validate the accuracy of the developed (on-chip) MSPE-HPLC-ICP-MS methods. The proposed methods were successfully applied to the speciation of selenium in selenium-enriched yeast cells. Analysis of approximately 800 cells by on-chip MSPE-HPLC-ICP-MS revealed that the average amounts of selenocystine (SeCys2) and selenomethionine (SeMet) in a single selenium-enriched yeast cell are in the order of subpicograms.