## 2 Results
### Static Adsorption and Desorption  
PGMA, PGMA-I, PGMA-II and PGMA-III were used to separate glucoerucin from crude extracts; the adsorption capacity and the ratios of adsorption and desorption of different adsorbents towards glucoerucin are shown in Figure 4. The adsorption/desorption ratio for PGMA-III towards glucoerucin was much higher than PGMA-I, PGMA-II and PGMA adsorbents. The high adsorption capacity of PGMA-III towards glucoerucin could be attributed to the strong interaction between the functional group -N\({}^{+}\) (CH\({}_{3}\))\({}_{3}\) of PGMA-III and -SO\({}_{3}\)\({}^{-}\) moiety of glucoerucin. Consequently, PGMA-III adsorbent was selected for further investigations of the adsorption/desorption behavior towards glucoerucin. Figure 5 shows that the pH of crude extracts (pH range 2-10) had no significant effect on the adsorption capacities and adsorption/desorption ratios of PGMA-III. A high degree of ionic interaction still existed between the sulfate moiety -SO\({}_{3}\)\({}^{-}\) of glucoerucin and the -N\({}^{+}\)(CH\({}_{3}\))\({}_{3}\) functional group of adsorbent which was not influenced by the change in pH; the ionization of the functional group of  
Figure 4: Adsorption capacities and the adsorption/desorption ratios for PGMA, PGMA-I PGMA-II and PGMA- III towards glucoerucin. Figure 3: Morphology of prepared beads by SEM. (**a**) PGMA; (**b**) PGMA-I; (**c**) PGMA-II; (**d**) PGMA-III. glucoerucin also played a major role in the adsorption process by PGMA-III. The pH of the crude extracts was adjusted to 6.2 for subsequent experiments. The Langmuir equations and Freundlich equations are usually used to reveal the linearity fitting and interaction of solutes with the adsorbents [21; 22; 23]. The experimental data were fitted to the Langmuir equation:  
\[\mathrm{q_{e}=\frac{q_{0}Kc_{e}}{1+Kc_{e}}} \tag{1}\]  
where q is the adsorption capacity, K is the adsorption equilibrium constant (an empirical constant) and \(\mathrm{C_{e}}\) is the concentration of adsorbate at equilibrium. The experimental data were also fitted to the Freundlich equation:  
\[\mathrm{q_{e}=K_{f}C_{e}^{1/n}} \tag{2}\]  
where \(\mathrm{K_{f}}\) is the Freundlich constant (an indicator of adsorption capacity); and 1/n is an empirical constant related to the magnitude of the adsorption driving force [23]. Equilibrium adsorption isotherms for crude extracts of glucoerucin (40 mL) on PGMA-III (0.5 g) at different temperatures are summarized in Table 2. Although the correlation coefficients for the experimental fit of the adsorption of glucoerucin on PGMA-III were >0.99 for both the Langmuir and Freundlich models, the Freundlich isotherm could provide a better prediction of the adsorption behavior. From the Freundlich equation, adsorption is likely to occur when 1/n lies between 0.1 and 0.5; it is unlikely when 1/n value lies 0.5 and 1; and its occurrence is least likely if 1/n value exceeds 1 [24]. Table 2 shows that the 1/n values were between 0.10 and 0.30, indicating that adsorption of glucoerucin on PGMA-III was favored. The results also demonstrated that the adsorption increased with increasing temperature. This suggested that a low temperature would inhibit adsorption and that the adsorption was endothermic. The kinetics of adsorption of glucoerucin on PGMA-III adsorbent at 30 \({}^{\circ}\)C are shown in Figure 6; the adsorption capacity increased with adsorption time to reach equilibrium after 150 min. The adsorption behavior may be consistent with the Freundlich multimolecular layer adsorption model arising from the strong interaction between -N\({}^{+}\)(CH\({}_{3}\))\({}_{3}\) of PGMA-III and -SO\({}_{3}\)\({}^{-}\) moiety of glucoerucin. Two rate equations were used to determine the adsorption kinetics of glucoerucin on the PGMA-III adsorbent. Figure 5: Effect of crude extracts solution pH on the adsorption capacity and adsorption ratios of PGMA-III adsorbent towards glucoerucin. The pseudo-first-order rate equation of [PERSON] is one of the most widely used for the adsorption of solute from a solution [25].