Zinc acetate as a precipitant of unstable haemoglobins

Whereas the addition of four moles of zinc acetate to one of normal human haemoglobin at pH 7.4 results in a clear solution, addition to unstable haemoglobin results in precipitate formation. Within certain limits no false-positive results are obtained with methaemoglobin, and with fetal haemoglobin. With excess zinc, normal haemoglobin also precipitates, but this process is reversible and can be used for a rapid concentration of dilute solutions of normal haemoglobin.