Online preconcentration in capillary electrophoresis with contactless conductivity detection for sensitive determination of sorbic and benzoic acids in soy sauce

A sensitive method of online preconcentration followed by capillary electrophoresis with capacitively coupled contactless conductivity detection (CE-C4D) is evaluated as a novel approach for the determination of benzoic acid and sorbic acid in soy sauce. The online preconcentration technique, namely field-enhanced sample injection, coupled with CE-C4D were successfully developed and optimized. In order to reduce the complex matrix interference resulting from the constituents of soy sauce, a suitable sample clean-up procedure was also investigated for real sample pretreatment. Under optimized conditions, sorbic acid and benzoic acid were well separated within 10 min, and the detection limits were 0.05 μM (5.6 μg L−1) and 0.08 μM (9.8 μg L−1), respectively. The accuracy was tested by spiking 10.0 mg L−1 and 100.0 mg L−1 of standards in the soy sauce samples, and the recoveries were 95–99%, respectively. Results of this study show a great potential for the proposed method as a tool for the fast screening of benzoic acid and sorbic acid in a complex matrix.