Selenium (Se) is an essential trace element for humans and has many significant physiological functions, even though the range between the essentiality and toxicity of Se is very narrow (Jagtap et al. 2016). The toxicity, bioavailability, environmental transport mechanism, and chemoprotective activities of Se are highly related to its chemical form and oxidation state (Wang et al. 2016). Inorganic Se can be toxic at high concentrations, while the bioavailability of selenomethionine (SeMet) is higher than that of organic Se in living organisms (Hu et al. 2017). Therefore, it is of great significance to conduct Se speciation analyses.