Large?volume sample stacking with polarity switching for analysis of azo dyes in water samples by capillary electrophoresis

A simple, fast and efficient on-line pre-concentration method (large-volume sample stacking) by capillary electrophoresis was proposed for determination of azo dyes residues (allura red [AR], sunset yellow [SY] and tartrazine [TAR]) in water samples. Pre-concentration variables involved in the system were optimised using of a Box?Bhenken design. Under the optimal conditions: injection time 150.0 s, pre-concentration time 120.0 s and reverse potential ?8.0 kV, the proposed methodology improved the analytical sensibility achieving limits of detection of 21.0?41.4 g L?1 with enrichment factors of 82.1?210.8 fold. The large-volume sample stacking-capillary electrophoresis method was validated and applied to determine azo dyes residues in 20 water samples (bottled, spring and tap water). Two samples were positive for sunset yellow and tartrazine with a concentration of 25.3 and 30.2 g L?1 and % RSD less than 10.0% in all cases.