Simultaneous Determination of Four Basic Dyes in Soybean Products by Capillary Zone Electrophoresis Combined with Solid Phase Extraction

A method of capillary zone electrophoresis couple with solid phase extraction was applied to the simultaneous determination of basic orange 2, basic orange 21, basic orange 22 and auramine O in soybean products. The sample (2.000 g) was ultrasonically extracted twice with 5.00 mL of 50 mmol·L^-1 ammonium acetate solution, the extract was purified on Oasis HLB solid phase extraction column and the 4 target dyes were eluted with ammonia-acetonitrile (5+95) solution. The eluent was dried-up by nitrogen blowing and the residue was dissolved and diluted to 1.00 mL with acetonitrile-H₂O (25+75) solution. The target dyes were separated by capillary zone electrophoresis at 30℃ and 20 kV with 40 mmol·L^-1 potassium dihydrogen phosphate solution containing 20% (φ) acetonitrile as running buffer solution (pH 2.5) and detected with a UV detector at the wavelength of 210 nm. Separation of the 4 dyes from baseline was achieved within 7 min. The linearity ranges of the four basic dyes were all 1.25-50 mg·L^-1 and detection limits (3S/N) were in the range of 0.5-0.7 mg·kg^-1. Recovery rates obtained by standard addition method were 73.6%-93.1%, and RSDs (n=6) were less than 10%.