In all experiments the amount of the drug dissolved was measured in on-line mode using an Agilent 8453 UV–VIS flow-through
spectrophotometer equipped with 5 mm flow-through quartz cuvettes (Hellma, Mühlheim, Germany). Measurements were performed in 5-min intervals using the differential mode, where the
signal and background were recorded at 302 and 450 nm, respectively. All experiments were performed in triplicate.