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.

359 CHOLINE PROLINE IONIC LIQUID-FUNCTIONALIZED O 4 @SIO 2 FE3FE 43 2 Table I Linear Relati o n ship and Detection Limit Parameter Allura red Linear regression equation S = 4485152c + 240565 Linear range (μg/mL) 0.02–5.0 Correlation coeffi cient (r2) 0.9997 Limit of detection (ng/mL) 9.0 RSD (%) 3.8 14 times, and the extraction effi ciency was lower than 85.0% after being eluted 14 times, which proved that the material can be reused. ANALYTICAL APPLICATION The HPLC chro matogram of allura red standard solution (curve a) and samples before and after extraction (curve b,c) are shown in Figure 13. From Figure 13, the retention time (tR) values for allura red were 11.2 min, and the concentration of the allura red was sig- nifi cantly increased after extraction. Linear relationship and detection li mit. The linear equation, linear correla tion coeffi cient, linear range, relative standard deviation, and detection limit of the method in this article are listed in Table I. Comparison with other methods. The d eveloped method was compared w ith other methods reported in the literature for extraction and determination of allura red (Table II). From Table 2, it can be seen that this method has a wide linear range, low detection of limit, and short extraction time. Real sample analysis. To evaluate th e applicability of th e proposed method, two commer- cial lipsticks were extracted using the method and analyzed by HPLC. The analysis re- sults are shown in Table III. From Table 3, it can be known that allura red was measured in one of the lipstick samples, and the content of allura red in the lipstick was 16.78 mg/ kg. The recovery rate of allura red was 88.05–104.26%, which proved that the method can be used to determine the content of allura red in lipstick. Table II Comparison of Methods for Determination of Allura Red Method Extraction agent Linear range (μg/mL) Detection limit (ng/mL) Extraction time (min) Reference MSPE-LC-MS NH2-LDC-MP 0.05–5.0 9.0 - (14) M-dSPE-LC-MS MSPD 0.005–1.0 1.0 - (15) MSPE-HPLC Fe3O4-NH2@GO 0.005–1.5 2.0 15 (16) CSPE-UV T-1180 0.4–8.0 1.0 120 (17) CPE-UV Mixed micelles 0.02–1.4 8.0 50 (18) MSPE-HPLC Fe3O4@SiO2@IL 0.02–5.0 9.0 5 This work