The flow system was constructed with a sliding-bar injector
equipped with an electronic timer (Micronal, Brazil),
0.7-mm i.d. polyethylene tubes and Perspex joint points. An
Ismatec IPC-8 peristaltic pump equipped with Tygon tubes
was used for fluid propelling. A UV–vis spectrophotometer
(Hitachi, 3000) with a 10-mm optical path (80 L inner
volume) quartz flow cell (Hellma) was employed for signal
measurements. A mini-column was lab-made by using three
Perspex blocks attached by screws. The central block was
drilled to form one hollow cylinder (3-mm diameter, 15-mm
long) that was filled with the ion-exchange resin.