El-Ansary, A.L., et al. “Spectrophotometric Microdetermination of Divalent Cu, Ni, Pd and UO2 Ions Using Some Naphthoic Acid Azo Dyes ”. Asian Journal of Chemistry, vol. 5, no. 4, Mar. 2010, pp. 1057-6, https://asianpubs.org/index.php/ajchem/article/view/24974.