V.KIRAN KUMAR, M. RAMESWARA RAO, K. B. CHANDRA SEKHAR, and N. DEVANNA, “Direct and Derivative Spectrophotometric Determination of Copper(II) and Nickel(II) in Beer, Wine and Edible Oils”, ijpbs, vol. 1, no. 2, pp. 1–8, Jun. 2010.