Of interest, EDTA binds with 106- and 102-fold higher affinity to Zn2+ than to Ca2+ and Fe2+, respectively [123], and in plasma, free Ca2+ concentration (1.05–1.30 mmol/L) is “only” about 103-fold higher than free Zn2+ (0.1–2.0 µmol/L), while majority of iron in plasma is bound to transferrin.