Fraction of Zinc Available as Zinc Ions at Physiologic pH 7.4 The fraction of zinc available as Zn2+ at physiologic pH 7.4 varies from zero to one hundred percent dependent upon zinc-ligand binding power. Carbohydrates are extremly loosely bound by Zn2+ ions at physiologic pH and do not interefer with the release of Zn2+ ions. However, Zn2+ ions do react visibly with them, resulting in brown spots on white compressed lozenges Data to prepare this figure was published mainly by Guy Berthon, PhD, Director of Research, INSERM Unit 305, Toulousse, France, and Bruce D. Martin, PhD, Department of Chemistry, University of Virginia. Additional data was obtained from "Critical Stability Constants" Volumes 1 through 6, edited by Arthur E. Martell and Robert M. Smith, Texas A&M University. Additional information for zinc (Zn) and ligand first stability constant data is here. homepage - Zinc Acetate Lozenges for Common Colds