Study on simultaneous determination of arsenic speciation and selenium speciation in selenium-rich foods by HPLC-ICP-MS

[Objective] A method for the simultaneous determination of arsenate [As(Ⅲ)], Arsenate [As(Ⅴ)], monomethylarsenate (MMA), dimethylarsenate (DMA), Arsine betaine (AsB), methyl-selenocysteine (MeSeCys) and selenomide in food was developed by high performance liquid phase inductively coupled plasma mass spectrometry (HPLC-ICP-MS), and a total of 10 kinds of arsenic and selenium element forms of As and Se, including acid (SeMet), selenocysteine (SeCys2), selenite [Se(Ⅳ)] and selenate [Se(Ⅵ)] . [Methods] Taking selenium rich rice as the research object, the best extraction method was determined by comparing different extraction methods and different kinds of enzymes. Moreover, different chromatographic columns, mobile phase composition, mobile phase pH, mobile phase flow, mobile phase methanol content and column temperature were compared to determine the best extraction and separation conditions. [Results] The optimal separation conditions were using Aglient ZORBAX SB-Aq chromatographic column with 20 mmol/L citric acid + 5 mmol/L sodium hexane sulfonate + 4% methanol as the mobile phase gradient with pH values of 4.0 and 6.0 respectively. Elution was performed at a flow rate of 1.0 mL/min, and inductively coupled plasma mass spectrometry (ICP-MS) was detected using HEHe mode. The optimal extraction condition is Tris-HCl (pH 7.5) buffer solution adding 15 mg proteinase K and 15 mg proteinase E. This method can completely separate 10 different forms of arsenic and selenium within 5 minutes. In the range of 0～50 μg/L, the linear relationship between the forms of each element is good, and the correlation coefficient <i>R</i>>0.999 5. The detection limits of As(Ⅴ), MMA, As(Ⅲ), DMA, AsB, Se(Ⅵ), Se(Ⅳ), SeCys2, MeSeCys and SeMet are 0.10, 0.10, 0.12, 0.14, 0.22, 0.15, 0.15, 0.18, 0.12, 0.15 μg/L respectively. The spiked recovery rate ranged from 76.0% to 104.2%, and the relative standard deviation ranged from 1.1% to 8.5%. [Conclusion] This method is simple, fast, highly sensitive and fully meets the requirements for accurate quantitative analysis of arsenic and selenium speciation in selenium-rich foods.