The significance of electron spin resonance of the ascorbic acid radical in freeze dried human brain tumours and oedematous or normal periphery.

The ESR spectrum, attributed to the ascorbic acid (ascorbyl) radical and obtained by exposing freeze dried material to air, can not be used as proof for the occurrence of in vivo free radical reactions. Depending on the method of freeze drying, the content of blood or hemolyzed blood is the dominant factor in creating higher than normal ESR signals in brain or related tissue. These findings explain why the signal, though larger in many human brain tumours than in their surroundings, is not indicative of malignancy. No differences are seen between oedematous and normal tissue. The ascorbyl radical is definitely not stable in aqueous solution, which indicates that fresh tissue sections can also not be used to study in vivo radicals by ESR.