357 CHOLINE PROLINE IONIC LIQUID-FUNCTIONALIZED O 4 @SIO 2 FE3FE 43 2 in different volume ratios, it showed strong elution ability for allura red, and the elution rate can reach 98%. This phenomenon may be caused by the synergistic effect of acetone and potassium bromide. On the one hand, acetone and water molecules can form hydro- gen bonds, and the hydrogen bonding force was greater than the Van der Waals force, so acetone was attracted by the water molecules, and the water molecules repel the dye. KBr was ionized in water to produce ions, which attracted to hydrogen ions and hydroxide ions in water, separating acetone from water. On the other hand, allura red was eluted by Br- and dissolved in acetone. Therefore, 2 mol/L KBr/acetone (2:1, v/v) was fi nally selected as an eluent. Effect of eluent volume. The effect of eluent volume in the range of 2.0–10.0 mL on the elution rate of allura red was evaluated, and the result is shown in Figure 11. As the eluent volume increased, the elution rate gradually increased. When the eluent volume was 6.0 mL, the maximum value was reached therefore, the optimal eluent volume for this experiment was 6.0 mL, and the pre-enrichment factor of allura red was 6.7 times (sample volume/eluent volume). Effect of eluent time. The elution t ime was investigated i n the range of 2.0–10.0 min the results showed that the elution can be completed within 2 min, and the elution effi ciency was greater than 97%, so the optimal elution time was chosen as 2 min. Reuse times of Fe3O4@SiO2@[Ch][Pro] The reuse times of Fe3O4@SiO2@[Ch][Pro] were investigated, and the result is shown in Figure 12. From Figure 12, it could be reused Figure 11. Eff e c t of eluent volume, and 2.50 μg/mL allura red.

358 JOURNAL OF COSMETIC SCIENCE Figure 13. HPLC chr o matograms. (A) Allura red standard solution (5 μg·mL-1), (B) sample before extrac- tion, and (C) sample after extraction. Figure 12. Reuse t imes of Fe3O4@SiO2@[Ch][Pro], and 2.50 μg/mL allura red.