Chromatographic procedure and conditions
Soft drink samples were sonicated for 30 min before dilution. Sample A was diluted 5 times for TZ and SY. Sample B was diluted 5 times for TZ and 2 times for CR. Finally, sample C was diluted 10 times for SY and 5 times for CR. 10 μL of the diluted samples were enriched with a series of standard solutions to increase the concentration of the studied analyte. The mobile phases were 0.1 M sodium acetate buffer at pH 7.0 (mobile phase A) and acetonitrile (mobile phase B). The optimized gradient for dye separation is given in Table 1. All experiments were performed at 25 °C at a flow rate of 1 mL min−1. The time required for separation was 24 min and the injection volume was 20 μL. The detection wavelengths were 425 nm for TZ, 480 nm for SY and 520 nm for CR. These chromatographic conditions involve minor modifications from the original procedure