Spectral measurements were made with an ultraviolet-visible spectrophotometer (Varian-Cary Win UV 100). For each concentration, buffer solution were added. The solution was then diluted to the mark. The absorbance spectra of the complex solution were recorded from 350 to 700 nm. A total of 24 spectra reading were obtained. 5 were used to test the network whilst the remaining 19 were used for the training.