Ressalan, S., et al. “3-Hydroxy-3-M-Sulphonato (Sodium Salt) Phenyl-1-O-Nitrophenyltriazene: An Indicator for the Simultaneous Complexometric Determination of Cr(III) With Fe(III), Cu(II) and Ni(II)”. Asian Journal of Chemistry, vol. 10, no. 4, July 2012, pp. 922-7, https://asianpubs.org/index.php/ajchem/article/view/23751.