1. Gibalo, I.M., Analiticheskaya khimiya niobiya i tantala (Analytical Chemistry of Niobium and Tantalum), Moscow: Nauka, 1967.
2. Nashine, N. and Mishra, R.K., Extraction-spectrophometric determination of niobium with thiocyanate and N-hydroxy-N,N′-diphenylbenzamidine, J. Indian Chem. Soc., 1993, vol. 70, no. 7, pp. 661–662.
3. Chhakkar Anoop Kumar and Kakkar Lajpal Rai, Extractive spectrophotometric determination of niobium with 3-hydroxy-2-(2-thienyl)-4H-chromen-4-one, Fresenius’ J. Anal. Chem., 1995, vol. 351, mo. 8, pp. 720–723.
4. Gomis, D.B., Jimeno, S.A., and Sanz-Medel, A., Extraction-spectrophotometric determination of niobium with dibenzo-18-crown-6 and thiocyanate, Talanta, 1983. vol. 29, no. 9, pp. 761–765.
5. Nayak, A.N., Ramappa, P.G., Yathirajan, H.S., and Manjappa, S., Microdetermination of niobium (V) with imipramine hydrochloride, Acta Chim. Acad. Sci. Hung, 1983, vol. 111, no. 2, pp. 233–238.