3515 CHOLINE PROLINE IONIC LIQUID-FUNCTIONALIZED O 4 @SIO 2 FE3FE 43 2 curve were attributed to Fe-O and Si-O, respectively, which proved the successful synthe- sis of Fe3O4@SiO2. (ii) In curve b, the N-H stretching of amino acids and the O-H stretching of choline correspond to broad peaks around 3,400 cm-1, and the characteristic peaks (carboxylate anion stretching) of amino acid ionic liquids appeared around 1,590 cm-1. (iii) There were stretching vibration peaks of Fe-O and Si-O at 582 cm-1 and 1,042 cm-1 in curve c, and the characteristic of amino acid ionic liquids appeared (1,590 cm-1). These FT-IR data indicated that Fe3O4@SiO2@[Ch][Pro] have been successfully synthe- sized. Figure 3 was an SE M image (a, b) of Fe3O4@SiO2 and Fe3O4@SiO2@[Ch][Pro]. In Fig- ure 3A, it can be clearly observed that SiO2 was successfully wrapped on Fe3O4. Com- pared with Figure 3A, the particles on the surface of Fe3O4@SiO2 became larger in Figure 3B, which proved that [Ch][Pro] was successfully functionalized on the surface of Fe3O4@ SiO2. OPTIMIZATION OF EXTRAC TION CONDITIONS Effect of sorbent amou nt. The infl uence of sorb ent amount on the extraction effi ciency was evaluated different amounts of Fe3O4@SiO2@[Ch][Pro] (4.0–12.0 mg) were used for the same procedures, and the result is shown in Figure 4. From Figure 4, it can be seen that by increasing the amount of Fe3O4@SiO2@[Ch][Pro] from 4.0 to 8.0 mg, the extraction rate of allura red was slightly increased. The extraction effi ciency reached a maximum after 8.0 mg of sorbent therefore, 8.0 mg of Fe3O4@SiO2@[Ch][Pro] was selected to obtain higher extraction effi ciency. Effect of pH. pH was a signifi cant factor affecting the existing form of allura red during the extraction process. The effect of pH on the extraction of allura red was studied in the range between 4.0 and 10.0. It can be seen from Figure 5 that allura red had higher ex- traction effi ciency under acidic conditions. The reason for this phenomenon might be that allura red exists in the form of R-SO3- anion under acidic conditions, which exist as elec- trostatic force with choline cation of Fe3O4@SiO2@[Ch][Pro]. When pH was 7, the extraction rate gradually decreased, and the reason was attributed to the increase in OH- concentration, which competed with R-SO3- to adsorb on the nanoparticles (13). There- fore, pH 5.0 was selected in the following experimental step. F i gure 3. SEM image (A) Fe3O4@SiO2 and (B) Fe3O4@SiO2@[Ch][Pro].

352 JOURNAL OF COSMETIC SCIENCE 6 Fig u r e 5. Effect of pH on the extraction rate. Experimental conditions: 2.50 μg/mL allura red, 8.0 mg Fe3O4@SiO2@[Ch][Pro], and 2.0 mL buffer. F i g ure 4. Effect of Fe3O4@SiO2@[Ch][Pro] amount on extraction effi ciency. Experimental conditions: 2.50 μg/mL allura red and 2.0 mL buffer (pH = 5.0).