3537 CHOLINE PROLINE IONIC LIQUID-FUNCTIONALIZED O 4 @SIO 2 FE3FE 43 2 Effect of temperature. Th e effect of temperatur e on extraction was investigated from 5°C to 45°C. It was found that the temperature had little effect on the extraction effi ciency of allura red, and the extraction rates were all greater than 92% at selected temperatures. So the following experiment was performed at room temperature. Effect of extraction time. The contact time between a nalyte and adsorbent was an important factor affecting the adsorption process. The effect of the extraction time in range of 1–25 min was investigated. As shown in Figure 6, the extraction process started immediately, and the extraction rate increased sharply to 96% within 5 min, and then remained stable, so in this experiment, the extraction time was chosen as 5 min. Effect of ionic strength. T he ionic strength may aff ect the adsorption of allura red by mag- netic nanoparticles, so 0–6.0% (w/v) of NaCl was used as the electrolyte model to inves- tigate the effect of ionic strength on the adsorption. The results were shown in Figure 7. When NaCl was not added, the extraction effi ciency of allura red was the largest. As the concentration of NaCl in the system increased, the extraction effi ciency decreased. The reason for this phenomenon may be that the extraction was dominated by electrostatic force, Cl- and allura red competed for adsorption by choline cations, leading to a reduc- tion in the extraction rate. Therefore, no NaCl added was chosen in this experiment. Effect of sample volume. The effect of sample volume on the extraction effi ciency of allura red was explored in the range of 10.0–70.0 mL the results were shown in Figure 8. From Figure 6. Effect of time on extraction effi ciency. Experimental conditions: 2.50 μg/mL allura red, 8.0 mg Fe3O4@SiO2@[Ch][Pro], and 2.0 mL buffer (pH = 5.0).

354 JOURNAL OF COSMETIC SCIENCE 8 Figure 7 . Effect of ionic strength on extraction effi ciency. Experimental conditions: 2.50 μg/mL allura red, 8.0 mg Fe3O4@SiO2@[Ch][Pro], and 2.0 mL buffer (pH = 5.0). Figure 8. E ffect of sample volume. Experimental conditions: 10 μg allura red, 8.0 mg Fe3O4@SiO2@[Ch] [Pro], and 2.0 mL buffer (pH = 5.0).