Abstract: A new rapid, sensitive method for protein determination using capillary electrophoresis and specific colorimetric reaction of bicinchoninic acid (BCA) was established, assisted by microwave incubation. With 60 mmol/L boric acid buffer (pH 9.5) and inclusion additive of β-cyclodextrin, the complex of BCA-Cu+ and free BCA molecules were efficiently separated. The peak intensity of BCA-Cu+was higher than those of native proteins about two orders of magnitude at a low wavelength of 200 nm. The linear ranges of this method were from 2 to 200 mg/L for transferrin, and 2 to 100 mg/L for ricin. The limits of detection for transferrin and ricin were 0.33 and 0.37 mg/L, respectively. This method was also successfully applied in the determination of some ricin samples in the First International Proficiency Test on the quantification of ricin.

Key words: bicinchoninic acid (BCA), colorimetric reaction, Cu+, protein , β-cyclodextrin, capillary electrophoresis (CE)