## 2 Materials and Methods
### Chemical, Physical Chemical, and Morphological Properties of Hydrogels  
The dried hydrogel disks were characterized by attenuated total reflection in conjunction with infrared spectroscopy (ATR-FTIR) in a BRUKER Vertex 70 Infrared Spectrophotometer using a zinc selenide (ZnSe) crystal. thermogravimetric analysis (TGA) was performed in a Netzsch, model STA 449 F3 Jupiter, employing N\({}_{2}\) as the purge gas, at a flow rate of 50 mL min\({}^{-1}\). The temperature was ramped from 25 to 900 \({}^{\circ}\)C at a heating rate of 10 \({}^{\circ}\)C min\({}^{-1}\).  
The swelling index (SI) of the hydrogels (in wt%) was determined by the weight difference from the swollen hydrogel, left in ultrapure water, HCl 0.1 mol L\({}^{-1}\) (pH 2.0) or NaCl 0.1 mol L\({}^{-1}\) (pH 6.0) for 60 min, and the dried hydrogel. Water loss was evaluated by  
Figure 1: **(a)** Protocols for the formation of hydrogels modified with polypyrrole. In the first protocol, an alginate hydrogel containing polypyrrole particles is formed, while in the second protocol, alginate hydrogels are covered with a polypyrrole layer. All hydrogels were later applied as extraction phases in SPE (Solid Phase Extraction). **(b)** Structure of all chemicals used. ALG and PPy were used to form the hydrogels, and ATZ, CAF, and PRO were the CECs used to evaluate the extraction behavior of the composite.  
the difference between the previously swelled hydrogel (60 min in ultrapure water) and the dried hydrogel, at 60 \({}^{\circ}\)C.  
The dried hydrogel beads were frozen in liquid nitrogen and fractured for SEM analysis. The samples were sputtered with a gold layer and observed in a TESCAN @3 LMU equipment, operating at 5 kV.  
Application of Hydrogel Beads as Extraction Phases for Determination of Atrazine, Caffe, and Progesterone  
The composite hydrogels were evaluated as the extraction phase for atrazine (ATZ), caffeine (CAF), and progesterone (PRO) (Figure 1b). For this, 0.5 g of each hydrogel was hydrated with 10 mL of ultrapure water. Then, 50 mL of the mixed analyte solution (0.5 mg L\({}^{-1}\)) were percolated though the hydrogel beads in a Visiprep (Supelco\({}^{\otimes}\), Bellefonte, PA, USA) manifold system at a flow rate of 3 mL min\({}^{-1}\), for the Solid Phase Extraction (SPE) step. The system was connected to a vacuum pump (Prismatec\({}^{\otimes}\), Porto Alegre, Brazil) for drying and the analytes were desorbed from the beads by percolation of 5 mL of methanol. The extracts were dried and reconstituted in 1 mL of ethyl acetate and, finally, injected into the GC-MS system (GCMS2010 Plus (Shimadzu\({}^{\otimes}\), Kyoto, Tokyo) gas chromatograph coupled to a TQ8040 mass spectrometer with an AC5000 for determination of the analytes. Chromatographic separation was performed in an SH-Rtx-5 MS column (30 m \(\times\) 0.25 mm \(\times\) 0.25 mm--Shimadzu\({}^{\otimes}\)) with helium 5.0 as the carrier gas and a constant flow rate of 1.0 mL min\({}^{-1}\). The injection volume was 1 \(\upmu\)L in split injection mode (1:10 ratio). Both injector and ion source temperatures were maintained at 250 \({}^{\circ}\)C. The transfer line temperature was 300 \({}^{\circ}\)C. The initial GC oven temperature was kept at 180 \({}^{\circ}\)C for 4 min, followed by an increase in 25 \({}^{\circ}\)C min\({}^{-1}\) to 300 \({}^{\circ}\)C (4 min). The total analysis time was 13 min, and the mass spectrometer operated in single ion monitoring (SIM) mode with electron ionization at 70 eV. One quantification ion (for ATZ, \(m/z\) = 200, for CAF, \(m/z\) = 194, and for PRO, \(m/z\) = 124) and two confirmation ions (for ATZ, \(m/z\) = 173 and 215, for CAF, \(m/z\) = 109 and 193, and for PRO, \(m/z\) = 91 and 191) were employed for each analyte. GCMS solution software was used for data analysis.