Isoflavones are important natural phytoestrogens in soybean responsible for its nutrition effects. The content of isoflavones is a quality control standard in soybean derived food products such as soymilk. Currently, most protocols of sample preparation for isoflavone determination in soymilk and other liquid soybean products involves freeze-drying and time consuming extraction procedures. The lengthy sample pretreatment is not only tedious and expensive, but also may increase variations in analytical results.
In order to address this problem, Prof. LIAO Xun and co-workers in Chengdu Institute of Biology reported a facile and rapid magnetic solid-phase extraction (MSPE) of isoflavones from soymilk for subsequent high-performance liquid chromatography electrospray ionization tandem mass spectrometry (HPLC-ESI-MS/MS) analysis. The extraction was based on the selective binding of isoflavones to baicalin-functionalized magnetic nanoparticles. Briefly, baicalin-functionalized magnetic nanoparticles (BMNPs) were synthesized and added into soymilk solution, after complete adsorption and magnetic separation, isoflavones adsorbed on BMNPs were eluted out with organic solvent for the following HPLC-MS analysis. This analytical method had a linear calibration curve in the concentration range from 0.3 to 80 mg/L, LOD 0.03mg/L.
This is the first time that BMNPs were used in quantitative analysis. The interaction between baicalin and isoflavones ensured the specific enrichment of the minor isoflavones from the liquid system, and the magnetic nature of the BMNPs composite makes the isolation of analytes very easy to carry out. Coupled with fast HPLC-MS/MS quantification, this MSPE method showed promising application in the quality control of soymilk and other liquid soybean products, and can be extended to many relevant analytical area of interest.
This work has been published in Journal of Agricultural and Food Chemistry, and the related research result has been applied for the Chinese invention patent previously.