A Shimadzu (Japan) model 1601pc UV–vis double beam
spectrophotometer was used for recording the spectra and
absorbance measurements. The triacetylcellulose membranes
was placed and fixed inside the quartz cells of the spectrophotometer.
Measurements of pH were made using the commercially
available pH meter, Model 3020, produced by Jenway, UK. The
optode membrane immersed into a 104 M Cu2+ solution at
pH = 6 for about 2 min and then the absorbance of the membrane
was measured at 550 nm