Bhatt, Rekha, et al. “Spectrophotometric Determination of Nickel With 3-Hydroxy-3-Methyl-1-P-Methoxy Phenyl Triazene”. Asian Journal of Chemistry, vol. 7, no. 1, Mar. 2010, pp. 225-6, https://asianpubs.org/index.php/ajchem/article/view/24251.