Disodium hydrogen phosphate dodecahydrate

Citric acid monohydrate (≥ 99%), disodium hydrogen phosphate dodecahydrate (≥ 99%), EDTA (Ethylendiaminetetraacetic acid; p.a.), sodium chloride (p.a.), magnesium sulfate anhydrous (p.a.), Sodium sulfate anhydrous (p.a.) and hydrochloric acid (35%) were purchased from Lach:ner (Czech Republic). Magnesium nitrate hexahydrate (> 99%), ammonium (25%), methanol (LC–MS grade), acetonitrile (LC–MS grade), and water (LC–MS grade) were purchased from VWR (USA). Sodium hydroxide (> 98%) was purchased from Penta. Formic acid (LC–MS grade), enrofloxacin (> 99%), ciprofloxacin (> 98%), enrofloxacin-d₅ (> 99%), and ciprofloxacin-d₈ (> 99%) were purchased from Sigma Aldrich (USA). OASIS HLB (Hydrophylic-Lipophilic Balanced) cartridges (200 mg; 6 mL; particle diameter 25–35 μm) were purchased from WATERS (USA). Nitrogen (4.7) and argon (5.0) gas were purchased from Siad (Czech Republic). Nylon syringe filters (13 mm, 0.22 μm) were purchased from Chromservis (Czech Republic). Physico-chemical properties of FQs can be found in Table S1.

Both monomers, itaconic acid (IA) and N-isopropylacrylamide (NiPAAm), were purchased from Acros Organics (Belgium). N,N′-methylenebisacrylamide (MBA) from Serva Feinbiochemica (Germany) was used as the crosslinking agent. The initiator and accelerator, potassium persulfate (PPS) and potassium pyrosulfate (PPyroS), were obtained from Merck & Co., Inc. (Germany), and Acros, respectively. Lipase from Candida rugosa (CRL) was kindly obtained from Sigma-Aldrich Chemie Gmbh (Germany). NiPAAm was recrystallized from benzene/n-hexane mixture (35/75) before its utilization. Other materials were used as received, without purification. Different pH value aqueous media were prepared using hydrochloric acid (LaChema, Czech Republic), potassium chloride (Zorka Šabac, Serbia), sodium dihydrogen phosphate dihydrate, and disodium hydrogen phosphate dodecahydrate (Lach-Ner, s.r.o., Czech Republic). Molar concentrations of all buffer solutions used were 0.2 M. Distilled water was used for all syntheses and the preparation of the buffer solutions.