Dragondroff's method was used to test for the presence of alkaloids qualitatively, and a UV Spectrophotometer was used to estimate their quantitative content. This technique is predicated on the interaction between bromocresol green (BCG) and alkaloid. Article Estimation of total alkaloid in Chitrakadivati by UV-Spectrophotometer
You need to carry out 4 methods to cualitative: Mayer (White pellet), Dragendorff (Red pellet), Bouchardad (Brown pellet), and Vitali Morin (you can obserb a violet colour when add KOH, with this last method, you can meassure quantity marina a curve with a known alkaloid