High polar organic–inorganic hybrid coating stir bar sorptive extraction combined with high performance liquid chromatography–inductively coupled plasma mass spectrometry for the speciation of seleno-amino acids and seleno-oligopeptides in biological samples

Abstract

In this work, partially sulfonated polystyrene-titania (PSP-TiO2) organic–inorganic hybrid stir bar coating was prepared by sol–gel and blending methods, and a new method of PSP-TiO2 coating stir bar sorptive extraction (SBSE)-high performance liquid chromatography (HPLC)–inductively coupled plasma mass spectrometry (ICP-MS) was established for the analysis of seleno-amino acids (selenocystine (SeCys2), methylseleno-cysteine (MeSeCys), selenomethionine (SeMet) and selenoethionine (SeEt)) and seleno-oligopeptides (γ-glutamyl-Se-methyl-selenocysteine (γ-GluMeSeCys) and selenodiglutathione (GS-Se-SG)) in biological samples. The prepared high polar PSP-TiO2 hybrid coating avoided the swelling of PSP and cracking of TiO2 coating by combining the good film-forming property of PSP with the high mechanical strength of TiO2. The scanning electron microscope (SEM) showed that no obvious swelling and damage occurred for the PSP-TiO2 hybrid stir bar coating after 30 extraction/desorption cycles. The preparation reproducibility of PSP-TiO2 coated stir bar, evaluated with the relative standard deviations (RSDs), was in the range of 6.7–12.6% (n=5) in one batch, and 9.9–17.6% (n=7) among different batches. The limits of detection (LODs) of the developed method for six target selenium species were in the range of 50.2–185.5ngL−1 (as 77Se) and 45.9–158.8ngL−1 (as 82Se) with the RSDs within 4.9–11.7%. The dynamic linear range was found to cover three orders of magnitude with correlation coefficient of 0.9995–0.9999. The developed method was applied for the analysis of Certified Reference Material SELM-1 selenium enriched yeast and the determined values were in good agreement with the certified values. The method has also been applied for the analysis of seleno-amino acids and seleno-oligopeptides in human urine and garlic samples. Different from the conventional organic polymer SBSE coatings (such as polydimethylsiloxane, PDMS), the extraction mechanism of PSP-TiO2 organic–inorganic hybrid SBSE coating was based on the cation exchange interaction, which made it feasible to directly extract high polar seleno-amino acids and seleno-oligopeptides in biological samples without derivatization. This coating could also be suitable for stir bar sorptive extraction of other cationic compounds from the environmental and biological samples.