Cadmium ions in water are determined by UV-Vis spectrophotometry using a chelating agent like dithizone to form a colored complex. The absorbance of the extracted complex is measured at a specific wavelength, typically around 520 nm, and compared to a calibration curve.

Add a complexing agent like PAN and perform at various concentration .For PAN-Cd complex lamda max will around 555nm then plot the calibration curve ( Abs vs Con.)

Complexation reaction is pH dependent. Presence of other metal ions may interfere , so find a complexing agent specific to Cd2+ or pretreat to remove interfering ions