Analysis of isoflavones in soy drink by capillary zone electrophoresis coupled with electrospray ionization mass spectrometry

Capillary zone electrophoresis coupled with electrospray ionization mass spectrometry (CZE–ESI-MS) has been applied for the first time for the separation and quantification of isoflavones in soy products. The proposed method was successfully applied to the determination of seven isoflavones, including aglycones and glucosides, in soy drink. The target compounds were the glucosides daidzin and genistin, and the aglycones daidzein, genistein, formononetin, biochanin A and glycitein. During CE separation in positive mode, the analytes were present as anions, and MS detection was carried out in ESI positive-ion mode. To prevent the frequent drops in current and to improve the resolution in the separation of analytes in anionic form, a programmed nebulizing gas pressure (PNP) was applied along the analysis.Extraction of isoflavones from soy drinks was carried out by liquid–liquid extraction using ethanol. The proposed extraction procedure is simple, efficient, and affords reproducible results. Quantification of the isoflavones in soy drinks using the external standard method did not produce good results; therefore, both internal standard and standard addition quantification methods were used, obtaining significantly similar results. The detection limits found were lower than 3.2 μg L−1.

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► Separation and quantification of isoflavones by CE–ESI-MS.
► CE separation as anions in positive mode and ionization in ESI positive-ion mode.
► Programmed nebulizing gas pressure prevents drops in current and improves the resolution of anions.
► Analysis of isoflavones (glucosides and aglycones) in soy drink samples.