EDTA analogues – unconventional inhibitors of gypsum precipitation

•Four polyamino-polycarboxylates were tested as gypsum crystallization inhibitors.•The inhibitors differ from each other in the spacing between the amino groups.•The spacing between the amino groups exert a secondary effect on the efficiency of the inhibition.•The inhibition efficiency is strongly pH-dependent and the optimal pH is ligand specific.•The stability of the 1:1 complexes and the proton competition explains the differences observed.