Stability and spontaneous production of blood cyanide during heating

To investigate the effects of heat on blood cyanide concentrations, in vitro experiments were performed using a headspace gas chromatographic method. Cyanide concentrations were determined for solutions of human hemoglobin (Hb) at neutrality, and for blood which was sealed in a vial and incubated at 25, 50, 63, 75 and 90 degrees C for 1 h. Spontaneous cyanide production was also measured. Nearly all of the added cyanide was recovered in both the Hb and for blood samples which were heated below 63 degrees C. Cyanide recovery in Hb decreased in a temperature-dependent manner at temperatures above 75 degrees C, and more than half of the recovered cyanide was found to be in the free form. In contrast, cyanide in blood disappeared more rapidly, and a major portion of it existed in the bound form. Cyanide concentrations in Hb solutions which were heated at 90 degrees C dropped in the two phases; a rapid initial phase, followed by a slower process. Spontaneous cyanide production was observed at temperatures above 50 degrees C for Hb and above 63 degrees C for blood. Under optimal conditions (75 degrees C heating), about 0.2 mmol of cyanide was produced per mol heme of Hb.