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-(CD)-D-4) 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-(CD)-D-4 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 mu M (5.6 mu L-1) and 0.08 mu M (9.8 mu g 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. (C) 2010 Elsevier B.V. All rights reserved.