Table 1.

Stability constants of DTPA, EDTA and HEDTA chelating agents with different ions [[23], [24], [25], [26]].

Chelating agent	${\text{Ca}}^{2+}$	${\text{Mg}}^{2+}$	${\text{Fe}}^{2+}$	${\text{Fe}}^{3+}$	${\text{Ba}}^{2+}$	${\text{Sr}}^{2+}$	${\text{Al}}^{3+}$	${\text{Mn}}^{2+}$	${\text{Zn}}^{2+}$	${\text{Cu}}^{2+}$	${\text{Ni}}^{2+}$	${\text{Zr}}^{4+}$
DTPA	10.9	9.3	16.5	28	8.6	9.7	18.4	15.6	18.75	21	20.32	36.9
EDTA	10.7	8.7	14.3	25.7	7.7	8.6	16.1	13.5	17.5	19.7	18.62	29.9
HEDTA	8.4	7	12.2	19.8	6.2	6.92	15.6	10.9	14.7	18.3	17	–