Abstract: A new and simple method for the accurate determination of rhodamine B in ketchup, tomato sauce and chili powder samples by micellar electrokinetic capillary chromatography (MEKC) with laser-induced fluorescence detection was developed. The separation was performed on an uncoated fused silica capillary 75 μm i.d. and 30 cm total length (effective length: 20 cm). The separation buffer solution was consisited of 30 mmol/L sodium tetraborate, 20 mmol/L sodium sodecyl sulfonate (SDS), 20 mmol/L sodium deoxycholate and 0.2 g/L polyethyleneglycol 35000. A solution of 10 mmol/L SDS was used for sample extraction. The analysis could be completed within 10 min. A voltage of 8 kV was used for separation. The injection time and pressure was 5 s at 3.448 kPa. The excitation and emission wavelength was 488 nm and 520 nm, respectively. The corrected peak area and the concentration of rhodamine B had good linear relationships with correlation coefficient (r) of 0.9999 in the ranges of 0.02 mg/L - 1.28 mg/L. The limit of detection and limit of quantitation were 5 g/L (S/N = 3) and 15 ?g/L (S/N = 10), respectively. The intra-day and inter-day precisions of the method were all lower than 2%. The average recoveries of rhodamine B at three concentration levels (0.04, 0.16 and 0.64 mg/L) were in the ranges of 100.9%-105.8%. The MEKC method was used to determine the contents of rhodamine B in ketchup, tomato sauce and chili powder. A total of twenty-eight samples (three kinds of ketchup, three kinds of tomato sauce and 22 kinds of chili powder ) were analyzed. The results of CE-LIF were all lower than those of ultra performance liquid chromatography-fluorescence (UPLC-FLR) detection method. The possible reasons were analyzed.

Key words: micellar electrokinetic chromatography, laser-induced fluorescence detection, rhodamine B, chili powder, ketchup, sauce