therefore, the supernatant solutions from the adsorption studies were analyzed in the linear region and diluted accordingly. In a typical sorption experiment, 20.0 ± 0.2 mgof copolymers were added to vials. A 10 mM stock solution of PNPwas prepared in a 10 mM KH2PO4buffer at pH 4.6. 7.00 ml of PNPsolution was added to each vial containing sorbent and blank. Thesamples were mixed for 48 h at 295 K and then the absorbanceof the supernatant was measured using UV–vis spectroscopy aftersettling of insoluble sorbent material by centrifugation, as outlinedabove. The same procedure was applied at pH 9.00, where a 10 mMNaHCO3buffer was pH adjusted using 1 M NaOH. At pH 6.6, a 10 mMKH2PO4buffer was pH adjusted using 1 M NaOH.