Zheng, H.L., W. Fan, W.Y. Xie, F.Y. Ji, M.Z. Tan, and C. Yang. 2013. “Catalytic Spectrophotometric Determination of Ultra Trace-Level Copper(II) With Indigo Carmine”. Asian Journal of Chemistry 25 (17):9547-50. https://doi.org/10.14233/ajchem.2013.15068.