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Figure 1.
(a) HPLC chromatograms of the samples from the flowers of Hibiscus manihot L. (b) Chemical structures of seven target flavonoids. 1, rutin; 2, hyperin; 3, isoquercetin; 4, hibifolin; 5, myricetin; 6, quercetin-3′-O-glucoside; 7, quercetin.
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Figure 2.
The effect of (a) type and (b) concentration of ionic liquids on the extraction of seven target flavonoids from the flowers of Hibiscus manihot L.
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Figure 3.
The effect of (a) homogenate speed and (b) time on the extraction of seven target flavonoids from the flowers of Hibiscus manihot L.
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Figure 4.
Response surfaces representations for (a) & (b) rutin, (c) hyperin, (d) isoquercetin, (e) & (f) hibifolin, (g) myricetin, (h) quercetin-3′-O-glucoside and (i) quercetin in the flowers of Hibiscus manihot L. (a), (g) & (h) varying liquid/solid ratio and extraction temperature; (b), (c) & (e) varying liquid/solid ratio and extraction time; (d), (f) & (i) varying extraction temperature and extraction time.
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Figure 5.
Comparison of different extraction methods on the extraction yields of seven target flavonoids from the flowers of Hibiscus manihot L.
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Ionic liquid Anion Cation [C2mim]Br 1-ethyl-3-methylimidazolium Br− [C4mim]Br 1-butyl-3-methylimidazolium Br− [C6mim]Br 1-hexyl-3-methylimidazolium Br− [C8mim]Br 1-octyl-3-methylimidazolium Br− [C4mim]Cl 1-butyl-3-methylimidazolium Cl− [C4mim]BF4 1-butyl-3-methylimidazolium ${{\text{BF}^-_{ 4}}} $ 
[C4mim]H2PO4 1-butyl-3-methylimidazolium ${\text {H}_2{\text{PO}}_4^- }$ 
[C4mim]OH 1-butyl-3-methylimidazolium OH− Table 1.
Ionic liquids used in this study.
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Runs Factors Extraction yield (mg/g) X1a X2b X3c Y1 Y2 Y3 Y4 Y5 Y6 Y7 1 −1(20) −1(50) 0(15) 0.48 4.94 3.72 4.88 0.11 0.55 0.28 2 1(30) −1(50) 0(15) 0.44 3.78 3.06 3.18 0.07 0.40 0.23 3 −1(20) 1(70) 0(15) 0.67 5.63 4.32 5.87 0.16 0.58 0.35 4 1(30) 1(70) 0(15) 0.56 4.48 3.64 3.80 0.11 0.45 0.20 5 −1(20) 0(60) −1(10) 0.66 5.15 3.76 4.42 0.15 0.45 0.31 6 1(30) 0(60) −1(10) 0.54 4.65 3.17 3.40 0.10 0.40 0.23 7 −1(20) 0(60) 1(20) 0.84 5.84 4.33 4.04 0.13 0.56 0.25 8 1(30) 0(60) 1(20) 0.48 3.85 3.25 3.78 0.09 0.42 0.24 9 0(25) −1(50) −1(10) 0.51 4.24 3.07 3.07 0.10 0.39 0.21 10 0(25) 1(70) −1(10) 0.71 6.07 4.45 5.36 0.15 0.49 0.31 11 0(25) −1(50) 1(20) 0.60 4.56 3.72 4.92 0.14 0.53 0.23 12 0(25) 1(70) 1(20) 0.60 4.54 3.66 4.73 0.12 0.51 0.23 13 0(25) 0(60) 0(15) 0.90 6.80 4.42 7.42 0.17 0.79 0.40 14 0(25) 0(60) 0(15) 0.90 7.97 4.74 6.84 0.17 0.87 0.41 15 0(25) 0(60) 0(15) 0.94 7.32 5.04 7.46 0.16 0.88 0.38 16 0(25) 0(60) 0(15) 0.93 7.56 4.96 6.99 0.17 0.83 0.45 17 0(25) 0(60) 0(15) 0.83 7.38 4.82 7.38 0.16 0.88 0.43 a Liquid/solid ratio (mL/g); b Extraction temperature (°C); c Extraction time (min). Table 2.
Results of the Box-Behnken design (BBD) for the extraction yields of seven target compounds from the flowers of Hibiscus manihot L.
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Variables Y1 Y2 Y3 Y4 Y5 Y6 Y7 F-value p-value F-value p-value F-value p-value F-value p-value F-value p-value F-value p-value F-value p-value Model 14.57 0.0009 25.78 0.0001 16.36 0.0007 22.40 0.0002 21.01 0.0003 57.28 <0.0001 17.53 0.0005 X1 14.15 0.0071 22.63 0.0021 23.95 0.0018 16.96 0.0045 46.74 0.0002 24.45 0.0017 15.40 0.0057 X2 9.47 0.0179 10.07 0.0156 16.74 0.0046 9.08 0.0196 23.05 0.0020 3.33 0.1109 3.91 0.0884 X3 0.27 0.6207 1.70 0.2340 0.69 0.4334 0.98 0.3543 0.11 0.7542 10.13 0.0154 2.26 0.1767 ${\text X_1^2 }$ 
33.36 0.0007 59.09 0.0001 32.58 0.0007 64.49 <0.0001 59.48 0.0001 141.92 <0.0001 27.99 0.0011 ${\text X_2^2 } $ 
44.16 0.0003 61.05 0.0001 23.03 0.0020 26.41 0.0013 18.15 0.0037 112.47 <0.0001 39.32 0.0004 ${\text X_3^2 } $ 
12.34 0.0098 46.84 0.0002 28.20 0.0011 57.83 0.0001 15.52 0.0056 168.60 <0.0001 46.19 0.0003 X1X2 0.33 0.5839 0.0007125 0.9794 0.00139 0.9713 0.17 0.6886 0.21 0.6624 0.090 0.7732 4.34 0.0757 X1X3 4.22 0.0791 4.34 0.0756 1.23 0.3048 0.74 0.4187 0.20 0.6674 1.95 0.2055 1.97 0.2037 X2X3 3.11 0.1212 6.73 0.0357 11.06 0.0127 8.24 0.0240 16.13 0.0051 3.28 0.1129 3.23 0.1155 Lack of fit 2.89 0.1660 0.33 0.8050 0.55 0.6754 4.10 0.1032 5.07 0.0755 0.29 0.8316 1.13 0.4360 R2 0.9493 0.9707 0.9546 0.9664 0.9643 0.9866 0.9575 Table 3.
ANOVA statistics of the quadratic model for the extraction yields of seven target compounds from the flowers of Hibiscus manihot L.
Figures
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Tables
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