Decomposition on freezing of reagents used in the ICSH-recommended method for the determination of total haemoglobin in blood; its nature, cause and prevention.

The decomposition on freezing of reagents used for the determination of total haemoglobin in blood was reinvestigated. When these reagents containing hexacyanoferrate(III) (ferricyanide) and cyanide are frozen and then thawed, hexacyanoferrate(III) is reduced to hexacyanoferrate(II) (ferrocyanide), cyanide being oxidized to (CN)2. At higher concentrations of the reactants than those present in the ICSH-recommended reagents, this reaction proceeds also at room temperature. During the process of freezing the reaction proceeds at low overall concentration of the reactants because the reactants become highly concentrated at the moving phase boundary. There is no evidence that the reaction that takes place on freezing can be prevented by the addition of ethanol, methanol, ethylene glycol or glycerol. Addition of these compounds does not affect the suitability of the reagent for use in haemoglobinometry.