A highly sensitive method is proposed to determine copper(II) ions by forming a stable complex through their
interaction with 4-(2′-benzothiazolylazo)-salicylic acid (BTAS) at room temperature and pH of about 5.0. The
complex gave a maximum absorption at λ = 485 nm with a molar absorptivity coefficient of 2.35⋅104
l/(mol⋅cm). The linear range for the copper determination is 0.63–5.04 mg/l. The method can be applied to
determine copper ions in different biological specimens like some drugs and water samples.