Sulfadiazine

Sulfadiazine, caffeine and atenolol of analytical grade were purchased from Dr. Ehrenstorfer GmbH (Augsburg, Germany). Molecular structures and selected properties of the target PhACs are presented in Table S1 (in Electronic Supplementary Material). Stock solutions of PhACs were prepared by dissolving 10 mg of each compound in 10 ml of methanol and were stored at 4 °C. Speciation of PhACs (shown in Fig. S1 a, b, c) was calculated using pKa values in Table S1 and Eqs. S1–S5.

All chemicals were of analytical reagent grade or better. Sulfadiazine (SDZ, 99.5%) was purchased from Dr. Ehrenstorfer GmbH (Augsburg, Germany). Q3/2 Accurel^® PP polypropylene microporous hollow fiber membrane (200-μm wall thickness, 600-μm inner diameter, 0.2-μm pore size, and 75% porosity) was obtained from Membrana GmbH (Wuppertal, Germany). All solutions and dilutions were prepared using ultrapure water from a Milli-Q Plus (Millipore, Billerica, MA, USA) water purification system.

Standards (purity >98%) of sulfadiazine, sulfamethazine, sulfamethoxazole, sulfapyridine, sulfamerazine, sulfachloropyridazine, sulfadimethoxine, sulfadoxine, sulfachinoxaline, sulfathiazole, sulfamethizole, trimethoprim, florfenicol, doxycycline, amoxicillin, cefalexin, penicillin V, sarafloxacin d8 and ciprofloxacin were purchased (Dr. Ehrenstorfer, Augsburg, Germany) and stored at 4°C. HPLC water, acetonitrile, formic acid 98%, ammonium formate (Merck, Darmstadt, Germany) and acetic acid 100% were obtained from J.T.Baker, Mallinckrodt Inc, MO, USA. All antimicrobial stock solutions (1000 μg/mL) were prepared in methanol excepted AMX and LEX (1000 μg/mL) which were prepared in methanol and water (1:1). Stock solutions were then diluted up to 1 μg/mL for standard curve preparation.