G. Ramappa, P., and K. S. Ramachandra. “Extraction-Spectrophotometric Determination of Niobium in Steels and Columbite Using Metoclopramide and Thiocyanate*”. Asian Journal of Chemistry, vol. 1, no. 1, Mar. 2010, pp. 19-24, https://asianpubs.org/index.php/ajchem/article/view/25363.