3559 CHOLINE PROLINE IONIC LIQUID-FUNCTIONALIZED O 4 @SIO 2 FE3FE 43 2 Figure 8, with the increase in sample volume, the extraction rate of allura red reduced. The extraction rate was lower than 85.0% when the sample volume was more than 40 mL. Therefore, the system allowed a maximum sample volume of 40 mL. Adsorption (extraction) capa city. The adsorption (extraction) capacity of Fe3O4@SiO2@[Ch] [Pro] was investigated by changing the concentration of allura red. The results are shown in Figure 9. As can be seen from Figure 9, when the concentration of allura red in the system reached 40.0 μg·mL-1, the adsorption (extraction) reached saturation. The adsorp- tion (extraction) capacity of Fe3O4@SiO2@[Ch][Pro] for allura red was 65.4 mg/g. OPTIMIZATION OF ELUTION CONDITIO NS Eluent selection. The effect of different eluents on the elution rate of allura red was studied the results are shown in Figure 10A and B. As shown in Figure 10A, the elution rate of allura red by common organic solvents (ethanol and acetone) was very low. For 2 mol/L NaCl, KCl, and KBr, the elution effi ciency of allura red can reach 53.21, 52.14, and 65.94%, respectively. The reason for this phenomenon might be that the elution rate was greatly affected by anions, and the ionic radius of Br- is larger than that of Cl- there was an electrostatic effect between Br- and choline cations in the solution, so part allura red was eluted. As shown in Figure 10B, when 2 mol/L KBr solution was mixed with acetone Figure 9. A d s orption (extraction) capacity. Experimental conditions: 8.0 mg Fe3O4@SiO2@[Ch][Pro] and 2.0 mL buffer (pH = 5.0).

356 JOURNAL OF COSMETIC SCIENCE Figure 10. ( A ) Eluent selection. (B) Effect of potassium bromide/acetone, and 2.50 μg/mL allura red.