Rezaie, Behrooz, et al. “Direct Spectrophotometric Determination of Vanadium With 3-Hydroxy-3-Phenyl-1-P-Carboxyphenyltriazene ”. Asian Journal of Chemistry, vol. 6, no. 1, Mar. 2010, pp. 187-8, https://asianpubs.org/index.php/ajchem/article/view/24515.