Contaminants in real water are normally complicated. Surface charges of suspended colloidal particles can be either negative or positive. In this work, a series of amphoteric starch-based grafting flocculants (3-chloro-2-hydroxypropyl trimethyl ammonium chloride modified starch-graft-poly(acrylamide-co-acrylic acid)) denoted as SCPAMPAA were successfully synthesized with different grafting ratios and used for the removal of different charged contaminants from water. Various SCPAMPAA flocculants exhibited remarkably different flocculation performance and obeyed diverse flocculation mechanisms due to the differences in their structural characteristics. Therefore, precise control of the molecular structure of flocculants is of great significance to obtain the desired flocculation performance. To provide practically operational feasibility for the preparation of a predicted flocculant, a quantitative mathematical correlation between the preparation recipe and the structural features of SCPAMPAA were derived. The final well-designed flocculant demonstrated a high flocculation performance in aspects of optimal dosage, flocculation window and pH sensitivity for the removal of both negatively and positively charged colloidal contaminants from targeted wastewater. (C) 2014 Elsevier B.V. All rights reserved.