*3.1. Reagents*

Sulfamethazine (SMT) was purchased from Alfa Aesar (Kandel, Germany). Stock solutions of SMT (5000 µM) were prepared in methanol (spectroscopic grade, Reanal, Budapest, Hungary). Diluted solutions of SMT were prepared by evaporating the methanol under relatively low pressure, then SMT was dissolved in appropriate volumes of the phosphate buffer of interest. CDs, including β-cyclodextrin (BCD) and randomly methylated β-cyclodextrin (RAMEB) were obtained from CycloLab Cyclodextrin Research and Development Laboratory, Ltd. (Budapest, Hungary). All the other analytical grade chemicals were purchased from VWR International Ltd. (Debrecen, Hungary). Phosphate buffer solutions have been prepared by mixing (0.1 M) H3PO<sup>4</sup> and (0.1M) Na2HPO4, (0.01 M) H3PO<sup>4</sup> and (0.01 M) Na2HPO<sup>4</sup> or (0.01 M) KH2PO<sup>4</sup> and (0.01 M) Na2HPO<sup>4</sup> stock solutions until the requested pH 2, 5 or 7 were reached, respectively. Ultrapure water (conductivity < 0.1 µS/cm,) were prepared by an Adrona (Riga, Latvia) water purification system.
