Electronic Supplementary Material
Magnetic molecular imprint-based extraction of sulfonylurea herbicides and their determination by capillary liquid chromatography
María Jesús Lerma-Garcíaa,b, Mohammed Zougaghb,c and Angel Ríosa,b[(]
a Department of Analytical Chemistry and Food Technology, University of Castilla–La Mancha, Av. Camilo José Cela 10, E-13004, Ciudad Real, Spain
b Regional Institute for Applied Chemistry Research, IRICA, Av. Camilo José Cela 10, E-13004, Ciudad Real, Spain
c Albacete Science and Technology Park, E-02006, Albacete, Spain
Optimization of the MMIP working conditions
To evaluate the capability of the MMIP3 for the selective preconcentration of sulfonylurea herbicides from water samples, different parameters such as sample pH, adsorption time, elution conditions and mass of sorbent were optimized. A factor by factor method was used for the optimization of the parameters affecting the extraction efficiency. Experiments were initially carried out by adding 500 mg of MMIP3 in a conical flash containing 500 mL of a 0.5 ng mL−1 sulfonylurea herbicide standard aqueous solution adjusted at pH 5. The solution was mixed by mechanical agitation for 15 min. Then, the sulfonylurea herbicides retained in the MMIP3 were eluted using 5 mL of a methanol – acetic acid (90:10 v/v) mixture. The recovery percentage was calculated from the amount of sulfonylurea herbicides present in the starting sample and the amount of sulfonylurea herbicides obtained after the desorption stage. In all cases, three replicates were performed for each experiment.
In order to evaluate the pH dependence of the retention of sulfonylurea herbicides, the pH values of sample solution were adjusted to a range of 3 – 6. The effect of pH value on analyte recovery is shown in Fig. S1a. It was observed that at low pH values, the adsorption capacity was low for most analytes, reaching in all cases its maximum recovery value at a pH = 5. Thus, pH = 5 was selected for further studies. Next, the effect of the adsorption time on metsulfuron-methyl recovery, which was varied between 2 and 25 min, was also examined. As observed in Fig. S1b, 10 min were enough to achieve a complete recovery, being this time selected for the next experiments.
Different elution conditions, such as elution solvent composition, elution volume and desorption time were next optimized. The optimization of the elution solvent composition, which was composed by methanol and acetic acid at different percentages (ranged from 0 to 15 % acetic acid, v/v), was firstly addressed. As observed in Fig. S1c, recovery values of about 100% were obtained when the acetic acid percentage was 1%, which was selected for further studies. Next, the effect of the elution volume (0.5 – 5 mL) on metsulfuron-methyl recovery was studied. As observed in Fig. S1d, at least 2 mL were necessary to efficiently elute the adsorbed metsulfuron-methyl (recoveries of about 100%). Thus, and in order to improve the enrichment factor, the 2 mL containing the sulfonylurea herbicides were evaporated to dryness, and the extract was redissolved in 0.5 mL prior to capillary liquid chromatography determination.
On the other hand, the optimal desorption time was also evaluated. Different times, which ranged from 2 to 25 min, were tried. As observed in Fig. S1e, 10 min were enough to achieve a complete recovery, being this time selected for the next experiments. Finally, the optimal amount of MMIP used to quantitatively extract metsulfuron-methyl was also optimized. For this purpose, different amounts of MMIP3, ranging from 100 to 700 mg, were tried. As observed in Fig. S1f, recovery increased when the amount of MMIP3 was increased from 100 to 500 mg. When the amount was higher than 500 mg, any significant recovery improvement was obtained. Therefore, the optimal amount of sorbent was fixed at 500 mg.
Reusability of sorbents
The potential regeneration and stability of sorbents were also investigated. Sorbents could be reused after regenerating with 5 mL of deionized water. Moreover, it was observed that it was stable up to at least 20 retention–elution cycles and could be repeatedly used without significant loss of their uptake capacity.
Fig. S1 Effect of sample pH (a), adsorption time (b), acetic acid percentage (c), eluent volume (d), desorption time (e) and mass of sorbent (f) on the retention of metsulfuron-methyl in MMIP3. Initial experimental conditions: sulfonylurea herbicide concentration, 0.5 ng mL-1; sample volume, 500 mL; adsorption time, 15 min; elution solvent, methanol / acetic acid (90:10 v/v); elution volume, 5 mL; desorption time, 15 min; mass of sorbent, 500 mg
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E-mail address: (A. Ríos)