Off-line concentration of bisphenol A and three alkylphenols by SPE then on-line concentration and rapid separation by reverse-migration micellar electrokinetic chromatography

A method for separation of four environmentally important compounds (three alkylphenols and bisphenol A) by cycloclextrin-modified reverse-migration micellar electrokinetic chromatography (CD-RM-MEKC) has been optimized. On-line concentration, stacking using reverse-migrating micelles and a water plug (SRW), was used to improve the limit of detection. Two main factors affecting the efficiency of enhancement by SRW, injection sample length and water-plug length, are discussed in detail. Compared with the normal 2-s injection, more than 121-fold enhancement of peak area and more than 71-fold enhancement of peak height were achieved with 120-s sample injection after 120-s water-plug injection. With this optimized separation method and SRW technology, limits of detection were found to be 0.089, 0.030, 0.0091, and 0.033 mg L-1 for 4-nonylphenol, 4-tert-octylphenol, bisphenol A, and 4-tert-butylphenol, respectively. Calibration plots (R-2 greater than or equal to 0.9968) and relative standard deviations (RSD, %) of corrected peak areas and migration time were also satisfactory. Combined with off-line concentration by solid-phase extraction (SPE) this method might be used to determine these contaminants at ppb levels in groundwater samples.