Determination of benzoic acid and sorbic acid in food products using electrokinetic flow analysis–ion pair solid phase extraction–capillary zone electrophoresis

An electrokinetic flow analysis system (EFA), consisting of one electroosmotic pump, five solenoid valves and one on-line homemade solid phase extraction (SPE) unit, combined with capillary zone electrophoresis (CZE) was proposed to determine benzoic acid and sorbic acid in food products. Tetrabutylammonium bromide (TBAB) was adopted as an ion pair reagent to improve the retention of the preservatives on C8-bonded silica sorbent, which was also used to remove sample matrices. By using the SPE unit, the EFA–SPE–CZE system was able to perform the SPE operation and CZE separation simultaneously. With a modified interface of EFA and CZE, the buffer consumption was reduced to 130 μL for each running. The preservatives were separated and determined under optimized conditions with p-hydroxybenzoic acid as an internal standard. The relative standard deviation (R.S.D.) of peak area for each analyte was less than 3.1% (n = 5) and the limits of detection (LODs) ranged from 10 to 20 ng mL−1 (K = 3, n = 11).