K. Rokicka, M. Wójciak-Kosior, I. Sowa, and J. Tylus, “Chromatographic separation of oleanolic, ursolic and betulinic acid in plant extracts on amiopropyl silica using aqueous mobile phases”, Curr. Issues Pharm. Med. Sci., vol. 26, no. 3, pp. 296–298, Sep. 2013, doi: 10.12923/j.2084-980X/26.3/a.12.