The inventor of the glycine flavor mask for zinc gluconate lozenges asserts that they release 92% to 93% of their zinc as Zn2+ (see Godfrey et al., Journal of International Medical Research, 1992;20:234-246). However, analysis by a world-class solution chemist (Guy Berthon, PhD) demonstrates that there is no Zn2+ at physiologic pH with glycine in a 10-fold excess, although there is about 20% Zn2+ at salivary pH 5.0 which produces a slight drying sensation. Lack of activity in reducing the duration of common colds would be expected as the first stability constant for zinc and glycine is nearly identical to that for zinc and citric acid.
